![Linus Torvalds](/assets/img/avatar_default.png)
Pull timer updates from Thomas Gleixner: "Yet another big pile of changes: - More year 2038 work from Arnd slowly reaching the point where we need to think about the syscalls themself. - A new timer function which allows to conditionally (re)arm a timer only when it's either not running or the new expiry time is sooner than the armed expiry time. This allows to use a single timer for multiple timeout requirements w/o caring about the first expiry time at the call site. - A new NMI safe accessor to clock real time for the printk timestamp work. Can be used by tracing, perf as well if required. - A large number of timer setup conversions from Kees which got collected here because either maintainers requested so or they simply got ignored. As Kees pointed out already there are a few trivial merge conflicts and some redundant commits which was unavoidable due to the size of this conversion effort. - Avoid a redundant iteration in the timer wheel softirq processing. - Provide a mechanism to treat RTC implementations depending on their hardware properties, i.e. don't inflict the write at the 0.5 seconds boundary which originates from the PC CMOS RTC to all RTCs. No functional change as drivers need to be updated separately. - The usual small updates to core code clocksource drivers. Nothing really exciting" * 'timers-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (111 commits) timers: Add a function to start/reduce a timer pstore: Use ktime_get_real_fast_ns() instead of __getnstimeofday() timer: Prepare to change all DEFINE_TIMER() callbacks netfilter: ipvs: Convert timers to use timer_setup() scsi: qla2xxx: Convert timers to use timer_setup() block/aoe: discover_timer: Convert timers to use timer_setup() ide: Convert timers to use timer_setup() drbd: Convert timers to use timer_setup() mailbox: Convert timers to use timer_setup() crypto: Convert timers to use timer_setup() drivers/pcmcia: omap1: Fix error in automated timer conversion ARM: footbridge: Fix typo in timer conversion drivers/sgi-xp: Convert timers to use timer_setup() drivers/pcmcia: Convert timers to use timer_setup() drivers/memstick: Convert timers to use timer_setup() drivers/macintosh: Convert timers to use timer_setup() hwrng/xgene-rng: Convert timers to use timer_setup() auxdisplay: Convert timers to use timer_setup() sparc/led: Convert timers to use timer_setup() mips: ip22/32: Convert timers to use timer_setup() ...
2610 lines
79 KiB
C
2610 lines
79 KiB
C
/*
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* Read-Copy Update mechanism for mutual exclusion (tree-based version)
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* Internal non-public definitions that provide either classic
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* or preemptible semantics.
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation; either version 2 of the License, or
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* (at your option) any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program; if not, you can access it online at
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* http://www.gnu.org/licenses/gpl-2.0.html.
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*
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* Copyright Red Hat, 2009
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* Copyright IBM Corporation, 2009
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*
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* Author: Ingo Molnar <mingo@elte.hu>
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* Paul E. McKenney <paulmck@linux.vnet.ibm.com>
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*/
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#include <linux/delay.h>
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#include <linux/gfp.h>
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#include <linux/oom.h>
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#include <linux/sched/debug.h>
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#include <linux/smpboot.h>
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#include <linux/sched/isolation.h>
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#include <uapi/linux/sched/types.h>
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#include "../time/tick-internal.h"
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#ifdef CONFIG_RCU_BOOST
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#include "../locking/rtmutex_common.h"
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/*
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* Control variables for per-CPU and per-rcu_node kthreads. These
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* handle all flavors of RCU.
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*/
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static DEFINE_PER_CPU(struct task_struct *, rcu_cpu_kthread_task);
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DEFINE_PER_CPU(unsigned int, rcu_cpu_kthread_status);
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DEFINE_PER_CPU(unsigned int, rcu_cpu_kthread_loops);
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DEFINE_PER_CPU(char, rcu_cpu_has_work);
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#else /* #ifdef CONFIG_RCU_BOOST */
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/*
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* Some architectures do not define rt_mutexes, but if !CONFIG_RCU_BOOST,
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* all uses are in dead code. Provide a definition to keep the compiler
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* happy, but add WARN_ON_ONCE() to complain if used in the wrong place.
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* This probably needs to be excluded from -rt builds.
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*/
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#define rt_mutex_owner(a) ({ WARN_ON_ONCE(1); NULL; })
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#define rt_mutex_futex_unlock(x) WARN_ON_ONCE(1)
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#endif /* #else #ifdef CONFIG_RCU_BOOST */
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#ifdef CONFIG_RCU_NOCB_CPU
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static cpumask_var_t rcu_nocb_mask; /* CPUs to have callbacks offloaded. */
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static bool have_rcu_nocb_mask; /* Was rcu_nocb_mask allocated? */
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static bool __read_mostly rcu_nocb_poll; /* Offload kthread are to poll. */
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#endif /* #ifdef CONFIG_RCU_NOCB_CPU */
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/*
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* Check the RCU kernel configuration parameters and print informative
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* messages about anything out of the ordinary.
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*/
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static void __init rcu_bootup_announce_oddness(void)
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{
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if (IS_ENABLED(CONFIG_RCU_TRACE))
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pr_info("\tRCU event tracing is enabled.\n");
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if ((IS_ENABLED(CONFIG_64BIT) && RCU_FANOUT != 64) ||
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(!IS_ENABLED(CONFIG_64BIT) && RCU_FANOUT != 32))
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pr_info("\tCONFIG_RCU_FANOUT set to non-default value of %d\n",
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RCU_FANOUT);
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if (rcu_fanout_exact)
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pr_info("\tHierarchical RCU autobalancing is disabled.\n");
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if (IS_ENABLED(CONFIG_RCU_FAST_NO_HZ))
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pr_info("\tRCU dyntick-idle grace-period acceleration is enabled.\n");
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if (IS_ENABLED(CONFIG_PROVE_RCU))
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pr_info("\tRCU lockdep checking is enabled.\n");
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if (RCU_NUM_LVLS >= 4)
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pr_info("\tFour(or more)-level hierarchy is enabled.\n");
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if (RCU_FANOUT_LEAF != 16)
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pr_info("\tBuild-time adjustment of leaf fanout to %d.\n",
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RCU_FANOUT_LEAF);
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if (rcu_fanout_leaf != RCU_FANOUT_LEAF)
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pr_info("\tBoot-time adjustment of leaf fanout to %d.\n", rcu_fanout_leaf);
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if (nr_cpu_ids != NR_CPUS)
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pr_info("\tRCU restricting CPUs from NR_CPUS=%d to nr_cpu_ids=%u.\n", NR_CPUS, nr_cpu_ids);
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#ifdef CONFIG_RCU_BOOST
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pr_info("\tRCU priority boosting: priority %d delay %d ms.\n", kthread_prio, CONFIG_RCU_BOOST_DELAY);
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#endif
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if (blimit != DEFAULT_RCU_BLIMIT)
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pr_info("\tBoot-time adjustment of callback invocation limit to %ld.\n", blimit);
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if (qhimark != DEFAULT_RCU_QHIMARK)
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pr_info("\tBoot-time adjustment of callback high-water mark to %ld.\n", qhimark);
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if (qlowmark != DEFAULT_RCU_QLOMARK)
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pr_info("\tBoot-time adjustment of callback low-water mark to %ld.\n", qlowmark);
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if (jiffies_till_first_fqs != ULONG_MAX)
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pr_info("\tBoot-time adjustment of first FQS scan delay to %ld jiffies.\n", jiffies_till_first_fqs);
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if (jiffies_till_next_fqs != ULONG_MAX)
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pr_info("\tBoot-time adjustment of subsequent FQS scan delay to %ld jiffies.\n", jiffies_till_next_fqs);
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if (rcu_kick_kthreads)
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pr_info("\tKick kthreads if too-long grace period.\n");
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if (IS_ENABLED(CONFIG_DEBUG_OBJECTS_RCU_HEAD))
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pr_info("\tRCU callback double-/use-after-free debug enabled.\n");
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if (gp_preinit_delay)
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pr_info("\tRCU debug GP pre-init slowdown %d jiffies.\n", gp_preinit_delay);
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if (gp_init_delay)
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pr_info("\tRCU debug GP init slowdown %d jiffies.\n", gp_init_delay);
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if (gp_cleanup_delay)
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pr_info("\tRCU debug GP init slowdown %d jiffies.\n", gp_cleanup_delay);
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if (IS_ENABLED(CONFIG_RCU_EQS_DEBUG))
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pr_info("\tRCU debug extended QS entry/exit.\n");
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rcupdate_announce_bootup_oddness();
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}
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#ifdef CONFIG_PREEMPT_RCU
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RCU_STATE_INITIALIZER(rcu_preempt, 'p', call_rcu);
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static struct rcu_state *const rcu_state_p = &rcu_preempt_state;
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static struct rcu_data __percpu *const rcu_data_p = &rcu_preempt_data;
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static void rcu_report_exp_rnp(struct rcu_state *rsp, struct rcu_node *rnp,
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bool wake);
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/*
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* Tell them what RCU they are running.
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*/
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static void __init rcu_bootup_announce(void)
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{
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pr_info("Preemptible hierarchical RCU implementation.\n");
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rcu_bootup_announce_oddness();
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}
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/* Flags for rcu_preempt_ctxt_queue() decision table. */
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#define RCU_GP_TASKS 0x8
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#define RCU_EXP_TASKS 0x4
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#define RCU_GP_BLKD 0x2
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#define RCU_EXP_BLKD 0x1
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/*
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* Queues a task preempted within an RCU-preempt read-side critical
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* section into the appropriate location within the ->blkd_tasks list,
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* depending on the states of any ongoing normal and expedited grace
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* periods. The ->gp_tasks pointer indicates which element the normal
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* grace period is waiting on (NULL if none), and the ->exp_tasks pointer
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* indicates which element the expedited grace period is waiting on (again,
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* NULL if none). If a grace period is waiting on a given element in the
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* ->blkd_tasks list, it also waits on all subsequent elements. Thus,
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* adding a task to the tail of the list blocks any grace period that is
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* already waiting on one of the elements. In contrast, adding a task
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* to the head of the list won't block any grace period that is already
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* waiting on one of the elements.
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*
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* This queuing is imprecise, and can sometimes make an ongoing grace
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* period wait for a task that is not strictly speaking blocking it.
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* Given the choice, we needlessly block a normal grace period rather than
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* blocking an expedited grace period.
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*
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* Note that an endless sequence of expedited grace periods still cannot
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* indefinitely postpone a normal grace period. Eventually, all of the
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* fixed number of preempted tasks blocking the normal grace period that are
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* not also blocking the expedited grace period will resume and complete
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* their RCU read-side critical sections. At that point, the ->gp_tasks
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* pointer will equal the ->exp_tasks pointer, at which point the end of
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* the corresponding expedited grace period will also be the end of the
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* normal grace period.
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*/
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static void rcu_preempt_ctxt_queue(struct rcu_node *rnp, struct rcu_data *rdp)
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__releases(rnp->lock) /* But leaves rrupts disabled. */
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{
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int blkd_state = (rnp->gp_tasks ? RCU_GP_TASKS : 0) +
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(rnp->exp_tasks ? RCU_EXP_TASKS : 0) +
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(rnp->qsmask & rdp->grpmask ? RCU_GP_BLKD : 0) +
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(rnp->expmask & rdp->grpmask ? RCU_EXP_BLKD : 0);
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struct task_struct *t = current;
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lockdep_assert_held(&rnp->lock);
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WARN_ON_ONCE(rdp->mynode != rnp);
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WARN_ON_ONCE(rnp->level != rcu_num_lvls - 1);
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/*
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* Decide where to queue the newly blocked task. In theory,
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* this could be an if-statement. In practice, when I tried
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* that, it was quite messy.
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*/
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switch (blkd_state) {
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case 0:
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case RCU_EXP_TASKS:
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case RCU_EXP_TASKS + RCU_GP_BLKD:
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case RCU_GP_TASKS:
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case RCU_GP_TASKS + RCU_EXP_TASKS:
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/*
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* Blocking neither GP, or first task blocking the normal
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* GP but not blocking the already-waiting expedited GP.
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* Queue at the head of the list to avoid unnecessarily
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* blocking the already-waiting GPs.
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*/
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list_add(&t->rcu_node_entry, &rnp->blkd_tasks);
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break;
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case RCU_EXP_BLKD:
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case RCU_GP_BLKD:
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case RCU_GP_BLKD + RCU_EXP_BLKD:
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case RCU_GP_TASKS + RCU_EXP_BLKD:
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case RCU_GP_TASKS + RCU_GP_BLKD + RCU_EXP_BLKD:
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case RCU_GP_TASKS + RCU_EXP_TASKS + RCU_GP_BLKD + RCU_EXP_BLKD:
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/*
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* First task arriving that blocks either GP, or first task
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* arriving that blocks the expedited GP (with the normal
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* GP already waiting), or a task arriving that blocks
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* both GPs with both GPs already waiting. Queue at the
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* tail of the list to avoid any GP waiting on any of the
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* already queued tasks that are not blocking it.
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*/
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list_add_tail(&t->rcu_node_entry, &rnp->blkd_tasks);
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break;
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case RCU_EXP_TASKS + RCU_EXP_BLKD:
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case RCU_EXP_TASKS + RCU_GP_BLKD + RCU_EXP_BLKD:
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case RCU_GP_TASKS + RCU_EXP_TASKS + RCU_EXP_BLKD:
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/*
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* Second or subsequent task blocking the expedited GP.
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* The task either does not block the normal GP, or is the
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* first task blocking the normal GP. Queue just after
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* the first task blocking the expedited GP.
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*/
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list_add(&t->rcu_node_entry, rnp->exp_tasks);
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break;
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case RCU_GP_TASKS + RCU_GP_BLKD:
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case RCU_GP_TASKS + RCU_EXP_TASKS + RCU_GP_BLKD:
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/*
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* Second or subsequent task blocking the normal GP.
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* The task does not block the expedited GP. Queue just
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* after the first task blocking the normal GP.
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*/
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list_add(&t->rcu_node_entry, rnp->gp_tasks);
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break;
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default:
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/* Yet another exercise in excessive paranoia. */
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WARN_ON_ONCE(1);
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break;
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}
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/*
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* We have now queued the task. If it was the first one to
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* block either grace period, update the ->gp_tasks and/or
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* ->exp_tasks pointers, respectively, to reference the newly
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* blocked tasks.
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*/
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if (!rnp->gp_tasks && (blkd_state & RCU_GP_BLKD))
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rnp->gp_tasks = &t->rcu_node_entry;
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if (!rnp->exp_tasks && (blkd_state & RCU_EXP_BLKD))
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rnp->exp_tasks = &t->rcu_node_entry;
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WARN_ON_ONCE(!(blkd_state & RCU_GP_BLKD) !=
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!(rnp->qsmask & rdp->grpmask));
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WARN_ON_ONCE(!(blkd_state & RCU_EXP_BLKD) !=
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!(rnp->expmask & rdp->grpmask));
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raw_spin_unlock_rcu_node(rnp); /* interrupts remain disabled. */
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/*
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* Report the quiescent state for the expedited GP. This expedited
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* GP should not be able to end until we report, so there should be
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* no need to check for a subsequent expedited GP. (Though we are
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* still in a quiescent state in any case.)
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*/
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if (blkd_state & RCU_EXP_BLKD &&
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t->rcu_read_unlock_special.b.exp_need_qs) {
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t->rcu_read_unlock_special.b.exp_need_qs = false;
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rcu_report_exp_rdp(rdp->rsp, rdp, true);
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} else {
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WARN_ON_ONCE(t->rcu_read_unlock_special.b.exp_need_qs);
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}
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}
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/*
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* Record a preemptible-RCU quiescent state for the specified CPU. Note
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* that this just means that the task currently running on the CPU is
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* not in a quiescent state. There might be any number of tasks blocked
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* while in an RCU read-side critical section.
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*
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* As with the other rcu_*_qs() functions, callers to this function
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* must disable preemption.
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*/
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static void rcu_preempt_qs(void)
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{
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RCU_LOCKDEP_WARN(preemptible(), "rcu_preempt_qs() invoked with preemption enabled!!!\n");
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if (__this_cpu_read(rcu_data_p->cpu_no_qs.s)) {
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trace_rcu_grace_period(TPS("rcu_preempt"),
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__this_cpu_read(rcu_data_p->gpnum),
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TPS("cpuqs"));
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__this_cpu_write(rcu_data_p->cpu_no_qs.b.norm, false);
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barrier(); /* Coordinate with rcu_preempt_check_callbacks(). */
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current->rcu_read_unlock_special.b.need_qs = false;
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}
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}
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/*
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* We have entered the scheduler, and the current task might soon be
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* context-switched away from. If this task is in an RCU read-side
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* critical section, we will no longer be able to rely on the CPU to
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* record that fact, so we enqueue the task on the blkd_tasks list.
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* The task will dequeue itself when it exits the outermost enclosing
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* RCU read-side critical section. Therefore, the current grace period
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* cannot be permitted to complete until the blkd_tasks list entries
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* predating the current grace period drain, in other words, until
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* rnp->gp_tasks becomes NULL.
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*
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* Caller must disable interrupts.
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*/
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static void rcu_preempt_note_context_switch(bool preempt)
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{
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struct task_struct *t = current;
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struct rcu_data *rdp;
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struct rcu_node *rnp;
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lockdep_assert_irqs_disabled();
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WARN_ON_ONCE(!preempt && t->rcu_read_lock_nesting > 0);
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if (t->rcu_read_lock_nesting > 0 &&
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!t->rcu_read_unlock_special.b.blocked) {
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/* Possibly blocking in an RCU read-side critical section. */
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rdp = this_cpu_ptr(rcu_state_p->rda);
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rnp = rdp->mynode;
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raw_spin_lock_rcu_node(rnp);
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t->rcu_read_unlock_special.b.blocked = true;
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t->rcu_blocked_node = rnp;
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/*
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* Verify the CPU's sanity, trace the preemption, and
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* then queue the task as required based on the states
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* of any ongoing and expedited grace periods.
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*/
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WARN_ON_ONCE((rdp->grpmask & rcu_rnp_online_cpus(rnp)) == 0);
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WARN_ON_ONCE(!list_empty(&t->rcu_node_entry));
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trace_rcu_preempt_task(rdp->rsp->name,
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t->pid,
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(rnp->qsmask & rdp->grpmask)
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? rnp->gpnum
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: rnp->gpnum + 1);
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rcu_preempt_ctxt_queue(rnp, rdp);
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} else if (t->rcu_read_lock_nesting < 0 &&
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t->rcu_read_unlock_special.s) {
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/*
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* Complete exit from RCU read-side critical section on
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* behalf of preempted instance of __rcu_read_unlock().
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*/
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rcu_read_unlock_special(t);
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}
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/*
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* Either we were not in an RCU read-side critical section to
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* begin with, or we have now recorded that critical section
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* globally. Either way, we can now note a quiescent state
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* for this CPU. Again, if we were in an RCU read-side critical
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* section, and if that critical section was blocking the current
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* grace period, then the fact that the task has been enqueued
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* means that we continue to block the current grace period.
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*/
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rcu_preempt_qs();
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}
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/*
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* Check for preempted RCU readers blocking the current grace period
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* for the specified rcu_node structure. If the caller needs a reliable
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* answer, it must hold the rcu_node's ->lock.
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*/
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static int rcu_preempt_blocked_readers_cgp(struct rcu_node *rnp)
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{
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return rnp->gp_tasks != NULL;
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}
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|
/*
|
|
* Advance a ->blkd_tasks-list pointer to the next entry, instead
|
|
* returning NULL if at the end of the list.
|
|
*/
|
|
static struct list_head *rcu_next_node_entry(struct task_struct *t,
|
|
struct rcu_node *rnp)
|
|
{
|
|
struct list_head *np;
|
|
|
|
np = t->rcu_node_entry.next;
|
|
if (np == &rnp->blkd_tasks)
|
|
np = NULL;
|
|
return np;
|
|
}
|
|
|
|
/*
|
|
* Return true if the specified rcu_node structure has tasks that were
|
|
* preempted within an RCU read-side critical section.
|
|
*/
|
|
static bool rcu_preempt_has_tasks(struct rcu_node *rnp)
|
|
{
|
|
return !list_empty(&rnp->blkd_tasks);
|
|
}
|
|
|
|
/*
|
|
* Handle special cases during rcu_read_unlock(), such as needing to
|
|
* notify RCU core processing or task having blocked during the RCU
|
|
* read-side critical section.
|
|
*/
|
|
void rcu_read_unlock_special(struct task_struct *t)
|
|
{
|
|
bool empty_exp;
|
|
bool empty_norm;
|
|
bool empty_exp_now;
|
|
unsigned long flags;
|
|
struct list_head *np;
|
|
bool drop_boost_mutex = false;
|
|
struct rcu_data *rdp;
|
|
struct rcu_node *rnp;
|
|
union rcu_special special;
|
|
|
|
/* NMI handlers cannot block and cannot safely manipulate state. */
|
|
if (in_nmi())
|
|
return;
|
|
|
|
local_irq_save(flags);
|
|
|
|
/*
|
|
* If RCU core is waiting for this CPU to exit its critical section,
|
|
* report the fact that it has exited. Because irqs are disabled,
|
|
* t->rcu_read_unlock_special cannot change.
|
|
*/
|
|
special = t->rcu_read_unlock_special;
|
|
if (special.b.need_qs) {
|
|
rcu_preempt_qs();
|
|
t->rcu_read_unlock_special.b.need_qs = false;
|
|
if (!t->rcu_read_unlock_special.s) {
|
|
local_irq_restore(flags);
|
|
return;
|
|
}
|
|
}
|
|
|
|
/*
|
|
* Respond to a request for an expedited grace period, but only if
|
|
* we were not preempted, meaning that we were running on the same
|
|
* CPU throughout. If we were preempted, the exp_need_qs flag
|
|
* would have been cleared at the time of the first preemption,
|
|
* and the quiescent state would be reported when we were dequeued.
|
|
*/
|
|
if (special.b.exp_need_qs) {
|
|
WARN_ON_ONCE(special.b.blocked);
|
|
t->rcu_read_unlock_special.b.exp_need_qs = false;
|
|
rdp = this_cpu_ptr(rcu_state_p->rda);
|
|
rcu_report_exp_rdp(rcu_state_p, rdp, true);
|
|
if (!t->rcu_read_unlock_special.s) {
|
|
local_irq_restore(flags);
|
|
return;
|
|
}
|
|
}
|
|
|
|
/* Hardware IRQ handlers cannot block, complain if they get here. */
|
|
if (in_irq() || in_serving_softirq()) {
|
|
lockdep_rcu_suspicious(__FILE__, __LINE__,
|
|
"rcu_read_unlock() from irq or softirq with blocking in critical section!!!\n");
|
|
pr_alert("->rcu_read_unlock_special: %#x (b: %d, enq: %d nq: %d)\n",
|
|
t->rcu_read_unlock_special.s,
|
|
t->rcu_read_unlock_special.b.blocked,
|
|
t->rcu_read_unlock_special.b.exp_need_qs,
|
|
t->rcu_read_unlock_special.b.need_qs);
|
|
local_irq_restore(flags);
|
|
return;
|
|
}
|
|
|
|
/* Clean up if blocked during RCU read-side critical section. */
|
|
if (special.b.blocked) {
|
|
t->rcu_read_unlock_special.b.blocked = false;
|
|
|
|
/*
|
|
* Remove this task from the list it blocked on. The task
|
|
* now remains queued on the rcu_node corresponding to the
|
|
* CPU it first blocked on, so there is no longer any need
|
|
* to loop. Retain a WARN_ON_ONCE() out of sheer paranoia.
|
|
*/
|
|
rnp = t->rcu_blocked_node;
|
|
raw_spin_lock_rcu_node(rnp); /* irqs already disabled. */
|
|
WARN_ON_ONCE(rnp != t->rcu_blocked_node);
|
|
WARN_ON_ONCE(rnp->level != rcu_num_lvls - 1);
|
|
empty_norm = !rcu_preempt_blocked_readers_cgp(rnp);
|
|
empty_exp = sync_rcu_preempt_exp_done(rnp);
|
|
smp_mb(); /* ensure expedited fastpath sees end of RCU c-s. */
|
|
np = rcu_next_node_entry(t, rnp);
|
|
list_del_init(&t->rcu_node_entry);
|
|
t->rcu_blocked_node = NULL;
|
|
trace_rcu_unlock_preempted_task(TPS("rcu_preempt"),
|
|
rnp->gpnum, t->pid);
|
|
if (&t->rcu_node_entry == rnp->gp_tasks)
|
|
rnp->gp_tasks = np;
|
|
if (&t->rcu_node_entry == rnp->exp_tasks)
|
|
rnp->exp_tasks = np;
|
|
if (IS_ENABLED(CONFIG_RCU_BOOST)) {
|
|
/* Snapshot ->boost_mtx ownership w/rnp->lock held. */
|
|
drop_boost_mutex = rt_mutex_owner(&rnp->boost_mtx) == t;
|
|
if (&t->rcu_node_entry == rnp->boost_tasks)
|
|
rnp->boost_tasks = np;
|
|
}
|
|
|
|
/*
|
|
* If this was the last task on the current list, and if
|
|
* we aren't waiting on any CPUs, report the quiescent state.
|
|
* Note that rcu_report_unblock_qs_rnp() releases rnp->lock,
|
|
* so we must take a snapshot of the expedited state.
|
|
*/
|
|
empty_exp_now = sync_rcu_preempt_exp_done(rnp);
|
|
if (!empty_norm && !rcu_preempt_blocked_readers_cgp(rnp)) {
|
|
trace_rcu_quiescent_state_report(TPS("preempt_rcu"),
|
|
rnp->gpnum,
|
|
0, rnp->qsmask,
|
|
rnp->level,
|
|
rnp->grplo,
|
|
rnp->grphi,
|
|
!!rnp->gp_tasks);
|
|
rcu_report_unblock_qs_rnp(rcu_state_p, rnp, flags);
|
|
} else {
|
|
raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
|
|
}
|
|
|
|
/* Unboost if we were boosted. */
|
|
if (IS_ENABLED(CONFIG_RCU_BOOST) && drop_boost_mutex)
|
|
rt_mutex_futex_unlock(&rnp->boost_mtx);
|
|
|
|
/*
|
|
* If this was the last task on the expedited lists,
|
|
* then we need to report up the rcu_node hierarchy.
|
|
*/
|
|
if (!empty_exp && empty_exp_now)
|
|
rcu_report_exp_rnp(rcu_state_p, rnp, true);
|
|
} else {
|
|
local_irq_restore(flags);
|
|
}
|
|
}
|
|
|
|
/*
|
|
* Dump detailed information for all tasks blocking the current RCU
|
|
* grace period on the specified rcu_node structure.
|
|
*/
|
|
static void rcu_print_detail_task_stall_rnp(struct rcu_node *rnp)
|
|
{
|
|
unsigned long flags;
|
|
struct task_struct *t;
|
|
|
|
raw_spin_lock_irqsave_rcu_node(rnp, flags);
|
|
if (!rcu_preempt_blocked_readers_cgp(rnp)) {
|
|
raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
|
|
return;
|
|
}
|
|
t = list_entry(rnp->gp_tasks->prev,
|
|
struct task_struct, rcu_node_entry);
|
|
list_for_each_entry_continue(t, &rnp->blkd_tasks, rcu_node_entry)
|
|
sched_show_task(t);
|
|
raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
|
|
}
|
|
|
|
/*
|
|
* Dump detailed information for all tasks blocking the current RCU
|
|
* grace period.
|
|
*/
|
|
static void rcu_print_detail_task_stall(struct rcu_state *rsp)
|
|
{
|
|
struct rcu_node *rnp = rcu_get_root(rsp);
|
|
|
|
rcu_print_detail_task_stall_rnp(rnp);
|
|
rcu_for_each_leaf_node(rsp, rnp)
|
|
rcu_print_detail_task_stall_rnp(rnp);
|
|
}
|
|
|
|
static void rcu_print_task_stall_begin(struct rcu_node *rnp)
|
|
{
|
|
pr_err("\tTasks blocked on level-%d rcu_node (CPUs %d-%d):",
|
|
rnp->level, rnp->grplo, rnp->grphi);
|
|
}
|
|
|
|
static void rcu_print_task_stall_end(void)
|
|
{
|
|
pr_cont("\n");
|
|
}
|
|
|
|
/*
|
|
* Scan the current list of tasks blocked within RCU read-side critical
|
|
* sections, printing out the tid of each.
|
|
*/
|
|
static int rcu_print_task_stall(struct rcu_node *rnp)
|
|
{
|
|
struct task_struct *t;
|
|
int ndetected = 0;
|
|
|
|
if (!rcu_preempt_blocked_readers_cgp(rnp))
|
|
return 0;
|
|
rcu_print_task_stall_begin(rnp);
|
|
t = list_entry(rnp->gp_tasks->prev,
|
|
struct task_struct, rcu_node_entry);
|
|
list_for_each_entry_continue(t, &rnp->blkd_tasks, rcu_node_entry) {
|
|
pr_cont(" P%d", t->pid);
|
|
ndetected++;
|
|
}
|
|
rcu_print_task_stall_end();
|
|
return ndetected;
|
|
}
|
|
|
|
/*
|
|
* Scan the current list of tasks blocked within RCU read-side critical
|
|
* sections, printing out the tid of each that is blocking the current
|
|
* expedited grace period.
|
|
*/
|
|
static int rcu_print_task_exp_stall(struct rcu_node *rnp)
|
|
{
|
|
struct task_struct *t;
|
|
int ndetected = 0;
|
|
|
|
if (!rnp->exp_tasks)
|
|
return 0;
|
|
t = list_entry(rnp->exp_tasks->prev,
|
|
struct task_struct, rcu_node_entry);
|
|
list_for_each_entry_continue(t, &rnp->blkd_tasks, rcu_node_entry) {
|
|
pr_cont(" P%d", t->pid);
|
|
ndetected++;
|
|
}
|
|
return ndetected;
|
|
}
|
|
|
|
/*
|
|
* Check that the list of blocked tasks for the newly completed grace
|
|
* period is in fact empty. It is a serious bug to complete a grace
|
|
* period that still has RCU readers blocked! This function must be
|
|
* invoked -before- updating this rnp's ->gpnum, and the rnp's ->lock
|
|
* must be held by the caller.
|
|
*
|
|
* Also, if there are blocked tasks on the list, they automatically
|
|
* block the newly created grace period, so set up ->gp_tasks accordingly.
|
|
*/
|
|
static void rcu_preempt_check_blocked_tasks(struct rcu_node *rnp)
|
|
{
|
|
struct task_struct *t;
|
|
|
|
RCU_LOCKDEP_WARN(preemptible(), "rcu_preempt_check_blocked_tasks() invoked with preemption enabled!!!\n");
|
|
WARN_ON_ONCE(rcu_preempt_blocked_readers_cgp(rnp));
|
|
if (rcu_preempt_has_tasks(rnp)) {
|
|
rnp->gp_tasks = rnp->blkd_tasks.next;
|
|
t = container_of(rnp->gp_tasks, struct task_struct,
|
|
rcu_node_entry);
|
|
trace_rcu_unlock_preempted_task(TPS("rcu_preempt-GPS"),
|
|
rnp->gpnum, t->pid);
|
|
}
|
|
WARN_ON_ONCE(rnp->qsmask);
|
|
}
|
|
|
|
/*
|
|
* Check for a quiescent state from the current CPU. When a task blocks,
|
|
* the task is recorded in the corresponding CPU's rcu_node structure,
|
|
* which is checked elsewhere.
|
|
*
|
|
* Caller must disable hard irqs.
|
|
*/
|
|
static void rcu_preempt_check_callbacks(void)
|
|
{
|
|
struct task_struct *t = current;
|
|
|
|
if (t->rcu_read_lock_nesting == 0) {
|
|
rcu_preempt_qs();
|
|
return;
|
|
}
|
|
if (t->rcu_read_lock_nesting > 0 &&
|
|
__this_cpu_read(rcu_data_p->core_needs_qs) &&
|
|
__this_cpu_read(rcu_data_p->cpu_no_qs.b.norm))
|
|
t->rcu_read_unlock_special.b.need_qs = true;
|
|
}
|
|
|
|
#ifdef CONFIG_RCU_BOOST
|
|
|
|
static void rcu_preempt_do_callbacks(void)
|
|
{
|
|
rcu_do_batch(rcu_state_p, this_cpu_ptr(rcu_data_p));
|
|
}
|
|
|
|
#endif /* #ifdef CONFIG_RCU_BOOST */
|
|
|
|
/**
|
|
* call_rcu() - Queue an RCU callback for invocation after a grace period.
|
|
* @head: structure to be used for queueing the RCU updates.
|
|
* @func: actual callback function to be invoked after the grace period
|
|
*
|
|
* The callback function will be invoked some time after a full grace
|
|
* period elapses, in other words after all pre-existing RCU read-side
|
|
* critical sections have completed. However, the callback function
|
|
* might well execute concurrently with RCU read-side critical sections
|
|
* that started after call_rcu() was invoked. RCU read-side critical
|
|
* sections are delimited by rcu_read_lock() and rcu_read_unlock(),
|
|
* and may be nested.
|
|
*
|
|
* Note that all CPUs must agree that the grace period extended beyond
|
|
* all pre-existing RCU read-side critical section. On systems with more
|
|
* than one CPU, this means that when "func()" is invoked, each CPU is
|
|
* guaranteed to have executed a full memory barrier since the end of its
|
|
* last RCU read-side critical section whose beginning preceded the call
|
|
* to call_rcu(). It also means that each CPU executing an RCU read-side
|
|
* critical section that continues beyond the start of "func()" must have
|
|
* executed a memory barrier after the call_rcu() but before the beginning
|
|
* of that RCU read-side critical section. Note that these guarantees
|
|
* include CPUs that are offline, idle, or executing in user mode, as
|
|
* well as CPUs that are executing in the kernel.
|
|
*
|
|
* Furthermore, if CPU A invoked call_rcu() and CPU B invoked the
|
|
* resulting RCU callback function "func()", then both CPU A and CPU B are
|
|
* guaranteed to execute a full memory barrier during the time interval
|
|
* between the call to call_rcu() and the invocation of "func()" -- even
|
|
* if CPU A and CPU B are the same CPU (but again only if the system has
|
|
* more than one CPU).
|
|
*/
|
|
void call_rcu(struct rcu_head *head, rcu_callback_t func)
|
|
{
|
|
__call_rcu(head, func, rcu_state_p, -1, 0);
|
|
}
|
|
EXPORT_SYMBOL_GPL(call_rcu);
|
|
|
|
/**
|
|
* synchronize_rcu - wait until a grace period has elapsed.
|
|
*
|
|
* Control will return to the caller some time after a full grace
|
|
* period has elapsed, in other words after all currently executing RCU
|
|
* read-side critical sections have completed. Note, however, that
|
|
* upon return from synchronize_rcu(), the caller might well be executing
|
|
* concurrently with new RCU read-side critical sections that began while
|
|
* synchronize_rcu() was waiting. RCU read-side critical sections are
|
|
* delimited by rcu_read_lock() and rcu_read_unlock(), and may be nested.
|
|
*
|
|
* See the description of synchronize_sched() for more detailed
|
|
* information on memory-ordering guarantees. However, please note
|
|
* that -only- the memory-ordering guarantees apply. For example,
|
|
* synchronize_rcu() is -not- guaranteed to wait on things like code
|
|
* protected by preempt_disable(), instead, synchronize_rcu() is -only-
|
|
* guaranteed to wait on RCU read-side critical sections, that is, sections
|
|
* of code protected by rcu_read_lock().
|
|
*/
|
|
void synchronize_rcu(void)
|
|
{
|
|
RCU_LOCKDEP_WARN(lock_is_held(&rcu_bh_lock_map) ||
|
|
lock_is_held(&rcu_lock_map) ||
|
|
lock_is_held(&rcu_sched_lock_map),
|
|
"Illegal synchronize_rcu() in RCU read-side critical section");
|
|
if (rcu_scheduler_active == RCU_SCHEDULER_INACTIVE)
|
|
return;
|
|
if (rcu_gp_is_expedited())
|
|
synchronize_rcu_expedited();
|
|
else
|
|
wait_rcu_gp(call_rcu);
|
|
}
|
|
EXPORT_SYMBOL_GPL(synchronize_rcu);
|
|
|
|
/**
|
|
* rcu_barrier - Wait until all in-flight call_rcu() callbacks complete.
|
|
*
|
|
* Note that this primitive does not necessarily wait for an RCU grace period
|
|
* to complete. For example, if there are no RCU callbacks queued anywhere
|
|
* in the system, then rcu_barrier() is within its rights to return
|
|
* immediately, without waiting for anything, much less an RCU grace period.
|
|
*/
|
|
void rcu_barrier(void)
|
|
{
|
|
_rcu_barrier(rcu_state_p);
|
|
}
|
|
EXPORT_SYMBOL_GPL(rcu_barrier);
|
|
|
|
/*
|
|
* Initialize preemptible RCU's state structures.
|
|
*/
|
|
static void __init __rcu_init_preempt(void)
|
|
{
|
|
rcu_init_one(rcu_state_p);
|
|
}
|
|
|
|
/*
|
|
* Check for a task exiting while in a preemptible-RCU read-side
|
|
* critical section, clean up if so. No need to issue warnings,
|
|
* as debug_check_no_locks_held() already does this if lockdep
|
|
* is enabled.
|
|
*/
|
|
void exit_rcu(void)
|
|
{
|
|
struct task_struct *t = current;
|
|
|
|
if (likely(list_empty(¤t->rcu_node_entry)))
|
|
return;
|
|
t->rcu_read_lock_nesting = 1;
|
|
barrier();
|
|
t->rcu_read_unlock_special.b.blocked = true;
|
|
__rcu_read_unlock();
|
|
}
|
|
|
|
#else /* #ifdef CONFIG_PREEMPT_RCU */
|
|
|
|
static struct rcu_state *const rcu_state_p = &rcu_sched_state;
|
|
|
|
/*
|
|
* Tell them what RCU they are running.
|
|
*/
|
|
static void __init rcu_bootup_announce(void)
|
|
{
|
|
pr_info("Hierarchical RCU implementation.\n");
|
|
rcu_bootup_announce_oddness();
|
|
}
|
|
|
|
/*
|
|
* Because preemptible RCU does not exist, we never have to check for
|
|
* CPUs being in quiescent states.
|
|
*/
|
|
static void rcu_preempt_note_context_switch(bool preempt)
|
|
{
|
|
}
|
|
|
|
/*
|
|
* Because preemptible RCU does not exist, there are never any preempted
|
|
* RCU readers.
|
|
*/
|
|
static int rcu_preempt_blocked_readers_cgp(struct rcu_node *rnp)
|
|
{
|
|
return 0;
|
|
}
|
|
|
|
/*
|
|
* Because there is no preemptible RCU, there can be no readers blocked.
|
|
*/
|
|
static bool rcu_preempt_has_tasks(struct rcu_node *rnp)
|
|
{
|
|
return false;
|
|
}
|
|
|
|
/*
|
|
* Because preemptible RCU does not exist, we never have to check for
|
|
* tasks blocked within RCU read-side critical sections.
|
|
*/
|
|
static void rcu_print_detail_task_stall(struct rcu_state *rsp)
|
|
{
|
|
}
|
|
|
|
/*
|
|
* Because preemptible RCU does not exist, we never have to check for
|
|
* tasks blocked within RCU read-side critical sections.
|
|
*/
|
|
static int rcu_print_task_stall(struct rcu_node *rnp)
|
|
{
|
|
return 0;
|
|
}
|
|
|
|
/*
|
|
* Because preemptible RCU does not exist, we never have to check for
|
|
* tasks blocked within RCU read-side critical sections that are
|
|
* blocking the current expedited grace period.
|
|
*/
|
|
static int rcu_print_task_exp_stall(struct rcu_node *rnp)
|
|
{
|
|
return 0;
|
|
}
|
|
|
|
/*
|
|
* Because there is no preemptible RCU, there can be no readers blocked,
|
|
* so there is no need to check for blocked tasks. So check only for
|
|
* bogus qsmask values.
|
|
*/
|
|
static void rcu_preempt_check_blocked_tasks(struct rcu_node *rnp)
|
|
{
|
|
WARN_ON_ONCE(rnp->qsmask);
|
|
}
|
|
|
|
/*
|
|
* Because preemptible RCU does not exist, it never has any callbacks
|
|
* to check.
|
|
*/
|
|
static void rcu_preempt_check_callbacks(void)
|
|
{
|
|
}
|
|
|
|
/*
|
|
* Because preemptible RCU does not exist, rcu_barrier() is just
|
|
* another name for rcu_barrier_sched().
|
|
*/
|
|
void rcu_barrier(void)
|
|
{
|
|
rcu_barrier_sched();
|
|
}
|
|
EXPORT_SYMBOL_GPL(rcu_barrier);
|
|
|
|
/*
|
|
* Because preemptible RCU does not exist, it need not be initialized.
|
|
*/
|
|
static void __init __rcu_init_preempt(void)
|
|
{
|
|
}
|
|
|
|
/*
|
|
* Because preemptible RCU does not exist, tasks cannot possibly exit
|
|
* while in preemptible RCU read-side critical sections.
|
|
*/
|
|
void exit_rcu(void)
|
|
{
|
|
}
|
|
|
|
#endif /* #else #ifdef CONFIG_PREEMPT_RCU */
|
|
|
|
#ifdef CONFIG_RCU_BOOST
|
|
|
|
static void rcu_wake_cond(struct task_struct *t, int status)
|
|
{
|
|
/*
|
|
* If the thread is yielding, only wake it when this
|
|
* is invoked from idle
|
|
*/
|
|
if (status != RCU_KTHREAD_YIELDING || is_idle_task(current))
|
|
wake_up_process(t);
|
|
}
|
|
|
|
/*
|
|
* Carry out RCU priority boosting on the task indicated by ->exp_tasks
|
|
* or ->boost_tasks, advancing the pointer to the next task in the
|
|
* ->blkd_tasks list.
|
|
*
|
|
* Note that irqs must be enabled: boosting the task can block.
|
|
* Returns 1 if there are more tasks needing to be boosted.
|
|
*/
|
|
static int rcu_boost(struct rcu_node *rnp)
|
|
{
|
|
unsigned long flags;
|
|
struct task_struct *t;
|
|
struct list_head *tb;
|
|
|
|
if (READ_ONCE(rnp->exp_tasks) == NULL &&
|
|
READ_ONCE(rnp->boost_tasks) == NULL)
|
|
return 0; /* Nothing left to boost. */
|
|
|
|
raw_spin_lock_irqsave_rcu_node(rnp, flags);
|
|
|
|
/*
|
|
* Recheck under the lock: all tasks in need of boosting
|
|
* might exit their RCU read-side critical sections on their own.
|
|
*/
|
|
if (rnp->exp_tasks == NULL && rnp->boost_tasks == NULL) {
|
|
raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
|
|
return 0;
|
|
}
|
|
|
|
/*
|
|
* Preferentially boost tasks blocking expedited grace periods.
|
|
* This cannot starve the normal grace periods because a second
|
|
* expedited grace period must boost all blocked tasks, including
|
|
* those blocking the pre-existing normal grace period.
|
|
*/
|
|
if (rnp->exp_tasks != NULL) {
|
|
tb = rnp->exp_tasks;
|
|
rnp->n_exp_boosts++;
|
|
} else {
|
|
tb = rnp->boost_tasks;
|
|
rnp->n_normal_boosts++;
|
|
}
|
|
rnp->n_tasks_boosted++;
|
|
|
|
/*
|
|
* We boost task t by manufacturing an rt_mutex that appears to
|
|
* be held by task t. We leave a pointer to that rt_mutex where
|
|
* task t can find it, and task t will release the mutex when it
|
|
* exits its outermost RCU read-side critical section. Then
|
|
* simply acquiring this artificial rt_mutex will boost task
|
|
* t's priority. (Thanks to tglx for suggesting this approach!)
|
|
*
|
|
* Note that task t must acquire rnp->lock to remove itself from
|
|
* the ->blkd_tasks list, which it will do from exit() if from
|
|
* nowhere else. We therefore are guaranteed that task t will
|
|
* stay around at least until we drop rnp->lock. Note that
|
|
* rnp->lock also resolves races between our priority boosting
|
|
* and task t's exiting its outermost RCU read-side critical
|
|
* section.
|
|
*/
|
|
t = container_of(tb, struct task_struct, rcu_node_entry);
|
|
rt_mutex_init_proxy_locked(&rnp->boost_mtx, t);
|
|
raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
|
|
/* Lock only for side effect: boosts task t's priority. */
|
|
rt_mutex_lock(&rnp->boost_mtx);
|
|
rt_mutex_unlock(&rnp->boost_mtx); /* Then keep lockdep happy. */
|
|
|
|
return READ_ONCE(rnp->exp_tasks) != NULL ||
|
|
READ_ONCE(rnp->boost_tasks) != NULL;
|
|
}
|
|
|
|
/*
|
|
* Priority-boosting kthread, one per leaf rcu_node.
|
|
*/
|
|
static int rcu_boost_kthread(void *arg)
|
|
{
|
|
struct rcu_node *rnp = (struct rcu_node *)arg;
|
|
int spincnt = 0;
|
|
int more2boost;
|
|
|
|
trace_rcu_utilization(TPS("Start boost kthread@init"));
|
|
for (;;) {
|
|
rnp->boost_kthread_status = RCU_KTHREAD_WAITING;
|
|
trace_rcu_utilization(TPS("End boost kthread@rcu_wait"));
|
|
rcu_wait(rnp->boost_tasks || rnp->exp_tasks);
|
|
trace_rcu_utilization(TPS("Start boost kthread@rcu_wait"));
|
|
rnp->boost_kthread_status = RCU_KTHREAD_RUNNING;
|
|
more2boost = rcu_boost(rnp);
|
|
if (more2boost)
|
|
spincnt++;
|
|
else
|
|
spincnt = 0;
|
|
if (spincnt > 10) {
|
|
rnp->boost_kthread_status = RCU_KTHREAD_YIELDING;
|
|
trace_rcu_utilization(TPS("End boost kthread@rcu_yield"));
|
|
schedule_timeout_interruptible(2);
|
|
trace_rcu_utilization(TPS("Start boost kthread@rcu_yield"));
|
|
spincnt = 0;
|
|
}
|
|
}
|
|
/* NOTREACHED */
|
|
trace_rcu_utilization(TPS("End boost kthread@notreached"));
|
|
return 0;
|
|
}
|
|
|
|
/*
|
|
* Check to see if it is time to start boosting RCU readers that are
|
|
* blocking the current grace period, and, if so, tell the per-rcu_node
|
|
* kthread to start boosting them. If there is an expedited grace
|
|
* period in progress, it is always time to boost.
|
|
*
|
|
* The caller must hold rnp->lock, which this function releases.
|
|
* The ->boost_kthread_task is immortal, so we don't need to worry
|
|
* about it going away.
|
|
*/
|
|
static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags)
|
|
__releases(rnp->lock)
|
|
{
|
|
struct task_struct *t;
|
|
|
|
lockdep_assert_held(&rnp->lock);
|
|
if (!rcu_preempt_blocked_readers_cgp(rnp) && rnp->exp_tasks == NULL) {
|
|
raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
|
|
return;
|
|
}
|
|
if (rnp->exp_tasks != NULL ||
|
|
(rnp->gp_tasks != NULL &&
|
|
rnp->boost_tasks == NULL &&
|
|
rnp->qsmask == 0 &&
|
|
ULONG_CMP_GE(jiffies, rnp->boost_time))) {
|
|
if (rnp->exp_tasks == NULL)
|
|
rnp->boost_tasks = rnp->gp_tasks;
|
|
raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
|
|
t = rnp->boost_kthread_task;
|
|
if (t)
|
|
rcu_wake_cond(t, rnp->boost_kthread_status);
|
|
} else {
|
|
raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
|
|
}
|
|
}
|
|
|
|
/*
|
|
* Wake up the per-CPU kthread to invoke RCU callbacks.
|
|
*/
|
|
static void invoke_rcu_callbacks_kthread(void)
|
|
{
|
|
unsigned long flags;
|
|
|
|
local_irq_save(flags);
|
|
__this_cpu_write(rcu_cpu_has_work, 1);
|
|
if (__this_cpu_read(rcu_cpu_kthread_task) != NULL &&
|
|
current != __this_cpu_read(rcu_cpu_kthread_task)) {
|
|
rcu_wake_cond(__this_cpu_read(rcu_cpu_kthread_task),
|
|
__this_cpu_read(rcu_cpu_kthread_status));
|
|
}
|
|
local_irq_restore(flags);
|
|
}
|
|
|
|
/*
|
|
* Is the current CPU running the RCU-callbacks kthread?
|
|
* Caller must have preemption disabled.
|
|
*/
|
|
static bool rcu_is_callbacks_kthread(void)
|
|
{
|
|
return __this_cpu_read(rcu_cpu_kthread_task) == current;
|
|
}
|
|
|
|
#define RCU_BOOST_DELAY_JIFFIES DIV_ROUND_UP(CONFIG_RCU_BOOST_DELAY * HZ, 1000)
|
|
|
|
/*
|
|
* Do priority-boost accounting for the start of a new grace period.
|
|
*/
|
|
static void rcu_preempt_boost_start_gp(struct rcu_node *rnp)
|
|
{
|
|
rnp->boost_time = jiffies + RCU_BOOST_DELAY_JIFFIES;
|
|
}
|
|
|
|
/*
|
|
* Create an RCU-boost kthread for the specified node if one does not
|
|
* already exist. We only create this kthread for preemptible RCU.
|
|
* Returns zero if all is well, a negated errno otherwise.
|
|
*/
|
|
static int rcu_spawn_one_boost_kthread(struct rcu_state *rsp,
|
|
struct rcu_node *rnp)
|
|
{
|
|
int rnp_index = rnp - &rsp->node[0];
|
|
unsigned long flags;
|
|
struct sched_param sp;
|
|
struct task_struct *t;
|
|
|
|
if (rcu_state_p != rsp)
|
|
return 0;
|
|
|
|
if (!rcu_scheduler_fully_active || rcu_rnp_online_cpus(rnp) == 0)
|
|
return 0;
|
|
|
|
rsp->boost = 1;
|
|
if (rnp->boost_kthread_task != NULL)
|
|
return 0;
|
|
t = kthread_create(rcu_boost_kthread, (void *)rnp,
|
|
"rcub/%d", rnp_index);
|
|
if (IS_ERR(t))
|
|
return PTR_ERR(t);
|
|
raw_spin_lock_irqsave_rcu_node(rnp, flags);
|
|
rnp->boost_kthread_task = t;
|
|
raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
|
|
sp.sched_priority = kthread_prio;
|
|
sched_setscheduler_nocheck(t, SCHED_FIFO, &sp);
|
|
wake_up_process(t); /* get to TASK_INTERRUPTIBLE quickly. */
|
|
return 0;
|
|
}
|
|
|
|
static void rcu_kthread_do_work(void)
|
|
{
|
|
rcu_do_batch(&rcu_sched_state, this_cpu_ptr(&rcu_sched_data));
|
|
rcu_do_batch(&rcu_bh_state, this_cpu_ptr(&rcu_bh_data));
|
|
rcu_preempt_do_callbacks();
|
|
}
|
|
|
|
static void rcu_cpu_kthread_setup(unsigned int cpu)
|
|
{
|
|
struct sched_param sp;
|
|
|
|
sp.sched_priority = kthread_prio;
|
|
sched_setscheduler_nocheck(current, SCHED_FIFO, &sp);
|
|
}
|
|
|
|
static void rcu_cpu_kthread_park(unsigned int cpu)
|
|
{
|
|
per_cpu(rcu_cpu_kthread_status, cpu) = RCU_KTHREAD_OFFCPU;
|
|
}
|
|
|
|
static int rcu_cpu_kthread_should_run(unsigned int cpu)
|
|
{
|
|
return __this_cpu_read(rcu_cpu_has_work);
|
|
}
|
|
|
|
/*
|
|
* Per-CPU kernel thread that invokes RCU callbacks. This replaces the
|
|
* RCU softirq used in flavors and configurations of RCU that do not
|
|
* support RCU priority boosting.
|
|
*/
|
|
static void rcu_cpu_kthread(unsigned int cpu)
|
|
{
|
|
unsigned int *statusp = this_cpu_ptr(&rcu_cpu_kthread_status);
|
|
char work, *workp = this_cpu_ptr(&rcu_cpu_has_work);
|
|
int spincnt;
|
|
|
|
for (spincnt = 0; spincnt < 10; spincnt++) {
|
|
trace_rcu_utilization(TPS("Start CPU kthread@rcu_wait"));
|
|
local_bh_disable();
|
|
*statusp = RCU_KTHREAD_RUNNING;
|
|
this_cpu_inc(rcu_cpu_kthread_loops);
|
|
local_irq_disable();
|
|
work = *workp;
|
|
*workp = 0;
|
|
local_irq_enable();
|
|
if (work)
|
|
rcu_kthread_do_work();
|
|
local_bh_enable();
|
|
if (*workp == 0) {
|
|
trace_rcu_utilization(TPS("End CPU kthread@rcu_wait"));
|
|
*statusp = RCU_KTHREAD_WAITING;
|
|
return;
|
|
}
|
|
}
|
|
*statusp = RCU_KTHREAD_YIELDING;
|
|
trace_rcu_utilization(TPS("Start CPU kthread@rcu_yield"));
|
|
schedule_timeout_interruptible(2);
|
|
trace_rcu_utilization(TPS("End CPU kthread@rcu_yield"));
|
|
*statusp = RCU_KTHREAD_WAITING;
|
|
}
|
|
|
|
/*
|
|
* Set the per-rcu_node kthread's affinity to cover all CPUs that are
|
|
* served by the rcu_node in question. The CPU hotplug lock is still
|
|
* held, so the value of rnp->qsmaskinit will be stable.
|
|
*
|
|
* We don't include outgoingcpu in the affinity set, use -1 if there is
|
|
* no outgoing CPU. If there are no CPUs left in the affinity set,
|
|
* this function allows the kthread to execute on any CPU.
|
|
*/
|
|
static void rcu_boost_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu)
|
|
{
|
|
struct task_struct *t = rnp->boost_kthread_task;
|
|
unsigned long mask = rcu_rnp_online_cpus(rnp);
|
|
cpumask_var_t cm;
|
|
int cpu;
|
|
|
|
if (!t)
|
|
return;
|
|
if (!zalloc_cpumask_var(&cm, GFP_KERNEL))
|
|
return;
|
|
for_each_leaf_node_possible_cpu(rnp, cpu)
|
|
if ((mask & leaf_node_cpu_bit(rnp, cpu)) &&
|
|
cpu != outgoingcpu)
|
|
cpumask_set_cpu(cpu, cm);
|
|
if (cpumask_weight(cm) == 0)
|
|
cpumask_setall(cm);
|
|
set_cpus_allowed_ptr(t, cm);
|
|
free_cpumask_var(cm);
|
|
}
|
|
|
|
static struct smp_hotplug_thread rcu_cpu_thread_spec = {
|
|
.store = &rcu_cpu_kthread_task,
|
|
.thread_should_run = rcu_cpu_kthread_should_run,
|
|
.thread_fn = rcu_cpu_kthread,
|
|
.thread_comm = "rcuc/%u",
|
|
.setup = rcu_cpu_kthread_setup,
|
|
.park = rcu_cpu_kthread_park,
|
|
};
|
|
|
|
/*
|
|
* Spawn boost kthreads -- called as soon as the scheduler is running.
|
|
*/
|
|
static void __init rcu_spawn_boost_kthreads(void)
|
|
{
|
|
struct rcu_node *rnp;
|
|
int cpu;
|
|
|
|
for_each_possible_cpu(cpu)
|
|
per_cpu(rcu_cpu_has_work, cpu) = 0;
|
|
BUG_ON(smpboot_register_percpu_thread(&rcu_cpu_thread_spec));
|
|
rcu_for_each_leaf_node(rcu_state_p, rnp)
|
|
(void)rcu_spawn_one_boost_kthread(rcu_state_p, rnp);
|
|
}
|
|
|
|
static void rcu_prepare_kthreads(int cpu)
|
|
{
|
|
struct rcu_data *rdp = per_cpu_ptr(rcu_state_p->rda, cpu);
|
|
struct rcu_node *rnp = rdp->mynode;
|
|
|
|
/* Fire up the incoming CPU's kthread and leaf rcu_node kthread. */
|
|
if (rcu_scheduler_fully_active)
|
|
(void)rcu_spawn_one_boost_kthread(rcu_state_p, rnp);
|
|
}
|
|
|
|
#else /* #ifdef CONFIG_RCU_BOOST */
|
|
|
|
static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags)
|
|
__releases(rnp->lock)
|
|
{
|
|
raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
|
|
}
|
|
|
|
static void invoke_rcu_callbacks_kthread(void)
|
|
{
|
|
WARN_ON_ONCE(1);
|
|
}
|
|
|
|
static bool rcu_is_callbacks_kthread(void)
|
|
{
|
|
return false;
|
|
}
|
|
|
|
static void rcu_preempt_boost_start_gp(struct rcu_node *rnp)
|
|
{
|
|
}
|
|
|
|
static void rcu_boost_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu)
|
|
{
|
|
}
|
|
|
|
static void __init rcu_spawn_boost_kthreads(void)
|
|
{
|
|
}
|
|
|
|
static void rcu_prepare_kthreads(int cpu)
|
|
{
|
|
}
|
|
|
|
#endif /* #else #ifdef CONFIG_RCU_BOOST */
|
|
|
|
#if !defined(CONFIG_RCU_FAST_NO_HZ)
|
|
|
|
/*
|
|
* Check to see if any future RCU-related work will need to be done
|
|
* by the current CPU, even if none need be done immediately, returning
|
|
* 1 if so. This function is part of the RCU implementation; it is -not-
|
|
* an exported member of the RCU API.
|
|
*
|
|
* Because we not have RCU_FAST_NO_HZ, just check whether this CPU needs
|
|
* any flavor of RCU.
|
|
*/
|
|
int rcu_needs_cpu(u64 basemono, u64 *nextevt)
|
|
{
|
|
*nextevt = KTIME_MAX;
|
|
return rcu_cpu_has_callbacks(NULL);
|
|
}
|
|
|
|
/*
|
|
* Because we do not have RCU_FAST_NO_HZ, don't bother cleaning up
|
|
* after it.
|
|
*/
|
|
static void rcu_cleanup_after_idle(void)
|
|
{
|
|
}
|
|
|
|
/*
|
|
* Do the idle-entry grace-period work, which, because CONFIG_RCU_FAST_NO_HZ=n,
|
|
* is nothing.
|
|
*/
|
|
static void rcu_prepare_for_idle(void)
|
|
{
|
|
}
|
|
|
|
/*
|
|
* Don't bother keeping a running count of the number of RCU callbacks
|
|
* posted because CONFIG_RCU_FAST_NO_HZ=n.
|
|
*/
|
|
static void rcu_idle_count_callbacks_posted(void)
|
|
{
|
|
}
|
|
|
|
#else /* #if !defined(CONFIG_RCU_FAST_NO_HZ) */
|
|
|
|
/*
|
|
* This code is invoked when a CPU goes idle, at which point we want
|
|
* to have the CPU do everything required for RCU so that it can enter
|
|
* the energy-efficient dyntick-idle mode. This is handled by a
|
|
* state machine implemented by rcu_prepare_for_idle() below.
|
|
*
|
|
* The following three proprocessor symbols control this state machine:
|
|
*
|
|
* RCU_IDLE_GP_DELAY gives the number of jiffies that a CPU is permitted
|
|
* to sleep in dyntick-idle mode with RCU callbacks pending. This
|
|
* is sized to be roughly one RCU grace period. Those energy-efficiency
|
|
* benchmarkers who might otherwise be tempted to set this to a large
|
|
* number, be warned: Setting RCU_IDLE_GP_DELAY too high can hang your
|
|
* system. And if you are -that- concerned about energy efficiency,
|
|
* just power the system down and be done with it!
|
|
* RCU_IDLE_LAZY_GP_DELAY gives the number of jiffies that a CPU is
|
|
* permitted to sleep in dyntick-idle mode with only lazy RCU
|
|
* callbacks pending. Setting this too high can OOM your system.
|
|
*
|
|
* The values below work well in practice. If future workloads require
|
|
* adjustment, they can be converted into kernel config parameters, though
|
|
* making the state machine smarter might be a better option.
|
|
*/
|
|
#define RCU_IDLE_GP_DELAY 4 /* Roughly one grace period. */
|
|
#define RCU_IDLE_LAZY_GP_DELAY (6 * HZ) /* Roughly six seconds. */
|
|
|
|
static int rcu_idle_gp_delay = RCU_IDLE_GP_DELAY;
|
|
module_param(rcu_idle_gp_delay, int, 0644);
|
|
static int rcu_idle_lazy_gp_delay = RCU_IDLE_LAZY_GP_DELAY;
|
|
module_param(rcu_idle_lazy_gp_delay, int, 0644);
|
|
|
|
/*
|
|
* Try to advance callbacks for all flavors of RCU on the current CPU, but
|
|
* only if it has been awhile since the last time we did so. Afterwards,
|
|
* if there are any callbacks ready for immediate invocation, return true.
|
|
*/
|
|
static bool __maybe_unused rcu_try_advance_all_cbs(void)
|
|
{
|
|
bool cbs_ready = false;
|
|
struct rcu_data *rdp;
|
|
struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);
|
|
struct rcu_node *rnp;
|
|
struct rcu_state *rsp;
|
|
|
|
/* Exit early if we advanced recently. */
|
|
if (jiffies == rdtp->last_advance_all)
|
|
return false;
|
|
rdtp->last_advance_all = jiffies;
|
|
|
|
for_each_rcu_flavor(rsp) {
|
|
rdp = this_cpu_ptr(rsp->rda);
|
|
rnp = rdp->mynode;
|
|
|
|
/*
|
|
* Don't bother checking unless a grace period has
|
|
* completed since we last checked and there are
|
|
* callbacks not yet ready to invoke.
|
|
*/
|
|
if ((rdp->completed != rnp->completed ||
|
|
unlikely(READ_ONCE(rdp->gpwrap))) &&
|
|
rcu_segcblist_pend_cbs(&rdp->cblist))
|
|
note_gp_changes(rsp, rdp);
|
|
|
|
if (rcu_segcblist_ready_cbs(&rdp->cblist))
|
|
cbs_ready = true;
|
|
}
|
|
return cbs_ready;
|
|
}
|
|
|
|
/*
|
|
* Allow the CPU to enter dyntick-idle mode unless it has callbacks ready
|
|
* to invoke. If the CPU has callbacks, try to advance them. Tell the
|
|
* caller to set the timeout based on whether or not there are non-lazy
|
|
* callbacks.
|
|
*
|
|
* The caller must have disabled interrupts.
|
|
*/
|
|
int rcu_needs_cpu(u64 basemono, u64 *nextevt)
|
|
{
|
|
struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);
|
|
unsigned long dj;
|
|
|
|
lockdep_assert_irqs_disabled();
|
|
|
|
/* Snapshot to detect later posting of non-lazy callback. */
|
|
rdtp->nonlazy_posted_snap = rdtp->nonlazy_posted;
|
|
|
|
/* If no callbacks, RCU doesn't need the CPU. */
|
|
if (!rcu_cpu_has_callbacks(&rdtp->all_lazy)) {
|
|
*nextevt = KTIME_MAX;
|
|
return 0;
|
|
}
|
|
|
|
/* Attempt to advance callbacks. */
|
|
if (rcu_try_advance_all_cbs()) {
|
|
/* Some ready to invoke, so initiate later invocation. */
|
|
invoke_rcu_core();
|
|
return 1;
|
|
}
|
|
rdtp->last_accelerate = jiffies;
|
|
|
|
/* Request timer delay depending on laziness, and round. */
|
|
if (!rdtp->all_lazy) {
|
|
dj = round_up(rcu_idle_gp_delay + jiffies,
|
|
rcu_idle_gp_delay) - jiffies;
|
|
} else {
|
|
dj = round_jiffies(rcu_idle_lazy_gp_delay + jiffies) - jiffies;
|
|
}
|
|
*nextevt = basemono + dj * TICK_NSEC;
|
|
return 0;
|
|
}
|
|
|
|
/*
|
|
* Prepare a CPU for idle from an RCU perspective. The first major task
|
|
* is to sense whether nohz mode has been enabled or disabled via sysfs.
|
|
* The second major task is to check to see if a non-lazy callback has
|
|
* arrived at a CPU that previously had only lazy callbacks. The third
|
|
* major task is to accelerate (that is, assign grace-period numbers to)
|
|
* any recently arrived callbacks.
|
|
*
|
|
* The caller must have disabled interrupts.
|
|
*/
|
|
static void rcu_prepare_for_idle(void)
|
|
{
|
|
bool needwake;
|
|
struct rcu_data *rdp;
|
|
struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);
|
|
struct rcu_node *rnp;
|
|
struct rcu_state *rsp;
|
|
int tne;
|
|
|
|
lockdep_assert_irqs_disabled();
|
|
if (rcu_is_nocb_cpu(smp_processor_id()))
|
|
return;
|
|
|
|
/* Handle nohz enablement switches conservatively. */
|
|
tne = READ_ONCE(tick_nohz_active);
|
|
if (tne != rdtp->tick_nohz_enabled_snap) {
|
|
if (rcu_cpu_has_callbacks(NULL))
|
|
invoke_rcu_core(); /* force nohz to see update. */
|
|
rdtp->tick_nohz_enabled_snap = tne;
|
|
return;
|
|
}
|
|
if (!tne)
|
|
return;
|
|
|
|
/*
|
|
* If a non-lazy callback arrived at a CPU having only lazy
|
|
* callbacks, invoke RCU core for the side-effect of recalculating
|
|
* idle duration on re-entry to idle.
|
|
*/
|
|
if (rdtp->all_lazy &&
|
|
rdtp->nonlazy_posted != rdtp->nonlazy_posted_snap) {
|
|
rdtp->all_lazy = false;
|
|
rdtp->nonlazy_posted_snap = rdtp->nonlazy_posted;
|
|
invoke_rcu_core();
|
|
return;
|
|
}
|
|
|
|
/*
|
|
* If we have not yet accelerated this jiffy, accelerate all
|
|
* callbacks on this CPU.
|
|
*/
|
|
if (rdtp->last_accelerate == jiffies)
|
|
return;
|
|
rdtp->last_accelerate = jiffies;
|
|
for_each_rcu_flavor(rsp) {
|
|
rdp = this_cpu_ptr(rsp->rda);
|
|
if (!rcu_segcblist_pend_cbs(&rdp->cblist))
|
|
continue;
|
|
rnp = rdp->mynode;
|
|
raw_spin_lock_rcu_node(rnp); /* irqs already disabled. */
|
|
needwake = rcu_accelerate_cbs(rsp, rnp, rdp);
|
|
raw_spin_unlock_rcu_node(rnp); /* irqs remain disabled. */
|
|
if (needwake)
|
|
rcu_gp_kthread_wake(rsp);
|
|
}
|
|
}
|
|
|
|
/*
|
|
* Clean up for exit from idle. Attempt to advance callbacks based on
|
|
* any grace periods that elapsed while the CPU was idle, and if any
|
|
* callbacks are now ready to invoke, initiate invocation.
|
|
*/
|
|
static void rcu_cleanup_after_idle(void)
|
|
{
|
|
lockdep_assert_irqs_disabled();
|
|
if (rcu_is_nocb_cpu(smp_processor_id()))
|
|
return;
|
|
if (rcu_try_advance_all_cbs())
|
|
invoke_rcu_core();
|
|
}
|
|
|
|
/*
|
|
* Keep a running count of the number of non-lazy callbacks posted
|
|
* on this CPU. This running counter (which is never decremented) allows
|
|
* rcu_prepare_for_idle() to detect when something out of the idle loop
|
|
* posts a callback, even if an equal number of callbacks are invoked.
|
|
* Of course, callbacks should only be posted from within a trace event
|
|
* designed to be called from idle or from within RCU_NONIDLE().
|
|
*/
|
|
static void rcu_idle_count_callbacks_posted(void)
|
|
{
|
|
__this_cpu_add(rcu_dynticks.nonlazy_posted, 1);
|
|
}
|
|
|
|
/*
|
|
* Data for flushing lazy RCU callbacks at OOM time.
|
|
*/
|
|
static atomic_t oom_callback_count;
|
|
static DECLARE_WAIT_QUEUE_HEAD(oom_callback_wq);
|
|
|
|
/*
|
|
* RCU OOM callback -- decrement the outstanding count and deliver the
|
|
* wake-up if we are the last one.
|
|
*/
|
|
static void rcu_oom_callback(struct rcu_head *rhp)
|
|
{
|
|
if (atomic_dec_and_test(&oom_callback_count))
|
|
wake_up(&oom_callback_wq);
|
|
}
|
|
|
|
/*
|
|
* Post an rcu_oom_notify callback on the current CPU if it has at
|
|
* least one lazy callback. This will unnecessarily post callbacks
|
|
* to CPUs that already have a non-lazy callback at the end of their
|
|
* callback list, but this is an infrequent operation, so accept some
|
|
* extra overhead to keep things simple.
|
|
*/
|
|
static void rcu_oom_notify_cpu(void *unused)
|
|
{
|
|
struct rcu_state *rsp;
|
|
struct rcu_data *rdp;
|
|
|
|
for_each_rcu_flavor(rsp) {
|
|
rdp = raw_cpu_ptr(rsp->rda);
|
|
if (rcu_segcblist_n_lazy_cbs(&rdp->cblist)) {
|
|
atomic_inc(&oom_callback_count);
|
|
rsp->call(&rdp->oom_head, rcu_oom_callback);
|
|
}
|
|
}
|
|
}
|
|
|
|
/*
|
|
* If low on memory, ensure that each CPU has a non-lazy callback.
|
|
* This will wake up CPUs that have only lazy callbacks, in turn
|
|
* ensuring that they free up the corresponding memory in a timely manner.
|
|
* Because an uncertain amount of memory will be freed in some uncertain
|
|
* timeframe, we do not claim to have freed anything.
|
|
*/
|
|
static int rcu_oom_notify(struct notifier_block *self,
|
|
unsigned long notused, void *nfreed)
|
|
{
|
|
int cpu;
|
|
|
|
/* Wait for callbacks from earlier instance to complete. */
|
|
wait_event(oom_callback_wq, atomic_read(&oom_callback_count) == 0);
|
|
smp_mb(); /* Ensure callback reuse happens after callback invocation. */
|
|
|
|
/*
|
|
* Prevent premature wakeup: ensure that all increments happen
|
|
* before there is a chance of the counter reaching zero.
|
|
*/
|
|
atomic_set(&oom_callback_count, 1);
|
|
|
|
for_each_online_cpu(cpu) {
|
|
smp_call_function_single(cpu, rcu_oom_notify_cpu, NULL, 1);
|
|
cond_resched_rcu_qs();
|
|
}
|
|
|
|
/* Unconditionally decrement: no need to wake ourselves up. */
|
|
atomic_dec(&oom_callback_count);
|
|
|
|
return NOTIFY_OK;
|
|
}
|
|
|
|
static struct notifier_block rcu_oom_nb = {
|
|
.notifier_call = rcu_oom_notify
|
|
};
|
|
|
|
static int __init rcu_register_oom_notifier(void)
|
|
{
|
|
register_oom_notifier(&rcu_oom_nb);
|
|
return 0;
|
|
}
|
|
early_initcall(rcu_register_oom_notifier);
|
|
|
|
#endif /* #else #if !defined(CONFIG_RCU_FAST_NO_HZ) */
|
|
|
|
#ifdef CONFIG_RCU_FAST_NO_HZ
|
|
|
|
static void print_cpu_stall_fast_no_hz(char *cp, int cpu)
|
|
{
|
|
struct rcu_dynticks *rdtp = &per_cpu(rcu_dynticks, cpu);
|
|
unsigned long nlpd = rdtp->nonlazy_posted - rdtp->nonlazy_posted_snap;
|
|
|
|
sprintf(cp, "last_accelerate: %04lx/%04lx, nonlazy_posted: %ld, %c%c",
|
|
rdtp->last_accelerate & 0xffff, jiffies & 0xffff,
|
|
ulong2long(nlpd),
|
|
rdtp->all_lazy ? 'L' : '.',
|
|
rdtp->tick_nohz_enabled_snap ? '.' : 'D');
|
|
}
|
|
|
|
#else /* #ifdef CONFIG_RCU_FAST_NO_HZ */
|
|
|
|
static void print_cpu_stall_fast_no_hz(char *cp, int cpu)
|
|
{
|
|
*cp = '\0';
|
|
}
|
|
|
|
#endif /* #else #ifdef CONFIG_RCU_FAST_NO_HZ */
|
|
|
|
/* Initiate the stall-info list. */
|
|
static void print_cpu_stall_info_begin(void)
|
|
{
|
|
pr_cont("\n");
|
|
}
|
|
|
|
/*
|
|
* Print out diagnostic information for the specified stalled CPU.
|
|
*
|
|
* If the specified CPU is aware of the current RCU grace period
|
|
* (flavor specified by rsp), then print the number of scheduling
|
|
* clock interrupts the CPU has taken during the time that it has
|
|
* been aware. Otherwise, print the number of RCU grace periods
|
|
* that this CPU is ignorant of, for example, "1" if the CPU was
|
|
* aware of the previous grace period.
|
|
*
|
|
* Also print out idle and (if CONFIG_RCU_FAST_NO_HZ) idle-entry info.
|
|
*/
|
|
static void print_cpu_stall_info(struct rcu_state *rsp, int cpu)
|
|
{
|
|
unsigned long delta;
|
|
char fast_no_hz[72];
|
|
struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu);
|
|
struct rcu_dynticks *rdtp = rdp->dynticks;
|
|
char *ticks_title;
|
|
unsigned long ticks_value;
|
|
|
|
if (rsp->gpnum == rdp->gpnum) {
|
|
ticks_title = "ticks this GP";
|
|
ticks_value = rdp->ticks_this_gp;
|
|
} else {
|
|
ticks_title = "GPs behind";
|
|
ticks_value = rsp->gpnum - rdp->gpnum;
|
|
}
|
|
print_cpu_stall_fast_no_hz(fast_no_hz, cpu);
|
|
delta = rdp->mynode->gpnum - rdp->rcu_iw_gpnum;
|
|
pr_err("\t%d-%c%c%c%c: (%lu %s) idle=%03x/%llx/%d softirq=%u/%u fqs=%ld %s\n",
|
|
cpu,
|
|
"O."[!!cpu_online(cpu)],
|
|
"o."[!!(rdp->grpmask & rdp->mynode->qsmaskinit)],
|
|
"N."[!!(rdp->grpmask & rdp->mynode->qsmaskinitnext)],
|
|
!IS_ENABLED(CONFIG_IRQ_WORK) ? '?' :
|
|
rdp->rcu_iw_pending ? (int)min(delta, 9UL) + '0' :
|
|
"!."[!delta],
|
|
ticks_value, ticks_title,
|
|
rcu_dynticks_snap(rdtp) & 0xfff,
|
|
rdtp->dynticks_nesting, rdtp->dynticks_nmi_nesting,
|
|
rdp->softirq_snap, kstat_softirqs_cpu(RCU_SOFTIRQ, cpu),
|
|
READ_ONCE(rsp->n_force_qs) - rsp->n_force_qs_gpstart,
|
|
fast_no_hz);
|
|
}
|
|
|
|
/* Terminate the stall-info list. */
|
|
static void print_cpu_stall_info_end(void)
|
|
{
|
|
pr_err("\t");
|
|
}
|
|
|
|
/* Zero ->ticks_this_gp for all flavors of RCU. */
|
|
static void zero_cpu_stall_ticks(struct rcu_data *rdp)
|
|
{
|
|
rdp->ticks_this_gp = 0;
|
|
rdp->softirq_snap = kstat_softirqs_cpu(RCU_SOFTIRQ, smp_processor_id());
|
|
}
|
|
|
|
/* Increment ->ticks_this_gp for all flavors of RCU. */
|
|
static void increment_cpu_stall_ticks(void)
|
|
{
|
|
struct rcu_state *rsp;
|
|
|
|
for_each_rcu_flavor(rsp)
|
|
raw_cpu_inc(rsp->rda->ticks_this_gp);
|
|
}
|
|
|
|
#ifdef CONFIG_RCU_NOCB_CPU
|
|
|
|
/*
|
|
* Offload callback processing from the boot-time-specified set of CPUs
|
|
* specified by rcu_nocb_mask. For each CPU in the set, there is a
|
|
* kthread created that pulls the callbacks from the corresponding CPU,
|
|
* waits for a grace period to elapse, and invokes the callbacks.
|
|
* The no-CBs CPUs do a wake_up() on their kthread when they insert
|
|
* a callback into any empty list, unless the rcu_nocb_poll boot parameter
|
|
* has been specified, in which case each kthread actively polls its
|
|
* CPU. (Which isn't so great for energy efficiency, but which does
|
|
* reduce RCU's overhead on that CPU.)
|
|
*
|
|
* This is intended to be used in conjunction with Frederic Weisbecker's
|
|
* adaptive-idle work, which would seriously reduce OS jitter on CPUs
|
|
* running CPU-bound user-mode computations.
|
|
*
|
|
* Offloading of callback processing could also in theory be used as
|
|
* an energy-efficiency measure because CPUs with no RCU callbacks
|
|
* queued are more aggressive about entering dyntick-idle mode.
|
|
*/
|
|
|
|
|
|
/* Parse the boot-time rcu_nocb_mask CPU list from the kernel parameters. */
|
|
static int __init rcu_nocb_setup(char *str)
|
|
{
|
|
alloc_bootmem_cpumask_var(&rcu_nocb_mask);
|
|
have_rcu_nocb_mask = true;
|
|
cpulist_parse(str, rcu_nocb_mask);
|
|
return 1;
|
|
}
|
|
__setup("rcu_nocbs=", rcu_nocb_setup);
|
|
|
|
static int __init parse_rcu_nocb_poll(char *arg)
|
|
{
|
|
rcu_nocb_poll = true;
|
|
return 0;
|
|
}
|
|
early_param("rcu_nocb_poll", parse_rcu_nocb_poll);
|
|
|
|
/*
|
|
* Wake up any no-CBs CPUs' kthreads that were waiting on the just-ended
|
|
* grace period.
|
|
*/
|
|
static void rcu_nocb_gp_cleanup(struct swait_queue_head *sq)
|
|
{
|
|
swake_up_all(sq);
|
|
}
|
|
|
|
/*
|
|
* Set the root rcu_node structure's ->need_future_gp field
|
|
* based on the sum of those of all rcu_node structures. This does
|
|
* double-count the root rcu_node structure's requests, but this
|
|
* is necessary to handle the possibility of a rcu_nocb_kthread()
|
|
* having awakened during the time that the rcu_node structures
|
|
* were being updated for the end of the previous grace period.
|
|
*/
|
|
static void rcu_nocb_gp_set(struct rcu_node *rnp, int nrq)
|
|
{
|
|
rnp->need_future_gp[(rnp->completed + 1) & 0x1] += nrq;
|
|
}
|
|
|
|
static struct swait_queue_head *rcu_nocb_gp_get(struct rcu_node *rnp)
|
|
{
|
|
return &rnp->nocb_gp_wq[rnp->completed & 0x1];
|
|
}
|
|
|
|
static void rcu_init_one_nocb(struct rcu_node *rnp)
|
|
{
|
|
init_swait_queue_head(&rnp->nocb_gp_wq[0]);
|
|
init_swait_queue_head(&rnp->nocb_gp_wq[1]);
|
|
}
|
|
|
|
/* Is the specified CPU a no-CBs CPU? */
|
|
bool rcu_is_nocb_cpu(int cpu)
|
|
{
|
|
if (have_rcu_nocb_mask)
|
|
return cpumask_test_cpu(cpu, rcu_nocb_mask);
|
|
return false;
|
|
}
|
|
|
|
/*
|
|
* Kick the leader kthread for this NOCB group. Caller holds ->nocb_lock
|
|
* and this function releases it.
|
|
*/
|
|
static void __wake_nocb_leader(struct rcu_data *rdp, bool force,
|
|
unsigned long flags)
|
|
__releases(rdp->nocb_lock)
|
|
{
|
|
struct rcu_data *rdp_leader = rdp->nocb_leader;
|
|
|
|
lockdep_assert_held(&rdp->nocb_lock);
|
|
if (!READ_ONCE(rdp_leader->nocb_kthread)) {
|
|
raw_spin_unlock_irqrestore(&rdp->nocb_lock, flags);
|
|
return;
|
|
}
|
|
if (rdp_leader->nocb_leader_sleep || force) {
|
|
/* Prior smp_mb__after_atomic() orders against prior enqueue. */
|
|
WRITE_ONCE(rdp_leader->nocb_leader_sleep, false);
|
|
del_timer(&rdp->nocb_timer);
|
|
raw_spin_unlock_irqrestore(&rdp->nocb_lock, flags);
|
|
smp_mb(); /* ->nocb_leader_sleep before swake_up(). */
|
|
swake_up(&rdp_leader->nocb_wq);
|
|
} else {
|
|
raw_spin_unlock_irqrestore(&rdp->nocb_lock, flags);
|
|
}
|
|
}
|
|
|
|
/*
|
|
* Kick the leader kthread for this NOCB group, but caller has not
|
|
* acquired locks.
|
|
*/
|
|
static void wake_nocb_leader(struct rcu_data *rdp, bool force)
|
|
{
|
|
unsigned long flags;
|
|
|
|
raw_spin_lock_irqsave(&rdp->nocb_lock, flags);
|
|
__wake_nocb_leader(rdp, force, flags);
|
|
}
|
|
|
|
/*
|
|
* Arrange to wake the leader kthread for this NOCB group at some
|
|
* future time when it is safe to do so.
|
|
*/
|
|
static void wake_nocb_leader_defer(struct rcu_data *rdp, int waketype,
|
|
const char *reason)
|
|
{
|
|
unsigned long flags;
|
|
|
|
raw_spin_lock_irqsave(&rdp->nocb_lock, flags);
|
|
if (rdp->nocb_defer_wakeup == RCU_NOCB_WAKE_NOT)
|
|
mod_timer(&rdp->nocb_timer, jiffies + 1);
|
|
WRITE_ONCE(rdp->nocb_defer_wakeup, waketype);
|
|
trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, reason);
|
|
raw_spin_unlock_irqrestore(&rdp->nocb_lock, flags);
|
|
}
|
|
|
|
/*
|
|
* Does the specified CPU need an RCU callback for the specified flavor
|
|
* of rcu_barrier()?
|
|
*/
|
|
static bool rcu_nocb_cpu_needs_barrier(struct rcu_state *rsp, int cpu)
|
|
{
|
|
struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu);
|
|
unsigned long ret;
|
|
#ifdef CONFIG_PROVE_RCU
|
|
struct rcu_head *rhp;
|
|
#endif /* #ifdef CONFIG_PROVE_RCU */
|
|
|
|
/*
|
|
* Check count of all no-CBs callbacks awaiting invocation.
|
|
* There needs to be a barrier before this function is called,
|
|
* but associated with a prior determination that no more
|
|
* callbacks would be posted. In the worst case, the first
|
|
* barrier in _rcu_barrier() suffices (but the caller cannot
|
|
* necessarily rely on this, not a substitute for the caller
|
|
* getting the concurrency design right!). There must also be
|
|
* a barrier between the following load an posting of a callback
|
|
* (if a callback is in fact needed). This is associated with an
|
|
* atomic_inc() in the caller.
|
|
*/
|
|
ret = atomic_long_read(&rdp->nocb_q_count);
|
|
|
|
#ifdef CONFIG_PROVE_RCU
|
|
rhp = READ_ONCE(rdp->nocb_head);
|
|
if (!rhp)
|
|
rhp = READ_ONCE(rdp->nocb_gp_head);
|
|
if (!rhp)
|
|
rhp = READ_ONCE(rdp->nocb_follower_head);
|
|
|
|
/* Having no rcuo kthread but CBs after scheduler starts is bad! */
|
|
if (!READ_ONCE(rdp->nocb_kthread) && rhp &&
|
|
rcu_scheduler_fully_active) {
|
|
/* RCU callback enqueued before CPU first came online??? */
|
|
pr_err("RCU: Never-onlined no-CBs CPU %d has CB %p\n",
|
|
cpu, rhp->func);
|
|
WARN_ON_ONCE(1);
|
|
}
|
|
#endif /* #ifdef CONFIG_PROVE_RCU */
|
|
|
|
return !!ret;
|
|
}
|
|
|
|
/*
|
|
* Enqueue the specified string of rcu_head structures onto the specified
|
|
* CPU's no-CBs lists. The CPU is specified by rdp, the head of the
|
|
* string by rhp, and the tail of the string by rhtp. The non-lazy/lazy
|
|
* counts are supplied by rhcount and rhcount_lazy.
|
|
*
|
|
* If warranted, also wake up the kthread servicing this CPUs queues.
|
|
*/
|
|
static void __call_rcu_nocb_enqueue(struct rcu_data *rdp,
|
|
struct rcu_head *rhp,
|
|
struct rcu_head **rhtp,
|
|
int rhcount, int rhcount_lazy,
|
|
unsigned long flags)
|
|
{
|
|
int len;
|
|
struct rcu_head **old_rhpp;
|
|
struct task_struct *t;
|
|
|
|
/* Enqueue the callback on the nocb list and update counts. */
|
|
atomic_long_add(rhcount, &rdp->nocb_q_count);
|
|
/* rcu_barrier() relies on ->nocb_q_count add before xchg. */
|
|
old_rhpp = xchg(&rdp->nocb_tail, rhtp);
|
|
WRITE_ONCE(*old_rhpp, rhp);
|
|
atomic_long_add(rhcount_lazy, &rdp->nocb_q_count_lazy);
|
|
smp_mb__after_atomic(); /* Store *old_rhpp before _wake test. */
|
|
|
|
/* If we are not being polled and there is a kthread, awaken it ... */
|
|
t = READ_ONCE(rdp->nocb_kthread);
|
|
if (rcu_nocb_poll || !t) {
|
|
trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
|
|
TPS("WakeNotPoll"));
|
|
return;
|
|
}
|
|
len = atomic_long_read(&rdp->nocb_q_count);
|
|
if (old_rhpp == &rdp->nocb_head) {
|
|
if (!irqs_disabled_flags(flags)) {
|
|
/* ... if queue was empty ... */
|
|
wake_nocb_leader(rdp, false);
|
|
trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
|
|
TPS("WakeEmpty"));
|
|
} else {
|
|
wake_nocb_leader_defer(rdp, RCU_NOCB_WAKE,
|
|
TPS("WakeEmptyIsDeferred"));
|
|
}
|
|
rdp->qlen_last_fqs_check = 0;
|
|
} else if (len > rdp->qlen_last_fqs_check + qhimark) {
|
|
/* ... or if many callbacks queued. */
|
|
if (!irqs_disabled_flags(flags)) {
|
|
wake_nocb_leader(rdp, true);
|
|
trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
|
|
TPS("WakeOvf"));
|
|
} else {
|
|
wake_nocb_leader_defer(rdp, RCU_NOCB_WAKE,
|
|
TPS("WakeOvfIsDeferred"));
|
|
}
|
|
rdp->qlen_last_fqs_check = LONG_MAX / 2;
|
|
} else {
|
|
trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, TPS("WakeNot"));
|
|
}
|
|
return;
|
|
}
|
|
|
|
/*
|
|
* This is a helper for __call_rcu(), which invokes this when the normal
|
|
* callback queue is inoperable. If this is not a no-CBs CPU, this
|
|
* function returns failure back to __call_rcu(), which can complain
|
|
* appropriately.
|
|
*
|
|
* Otherwise, this function queues the callback where the corresponding
|
|
* "rcuo" kthread can find it.
|
|
*/
|
|
static bool __call_rcu_nocb(struct rcu_data *rdp, struct rcu_head *rhp,
|
|
bool lazy, unsigned long flags)
|
|
{
|
|
|
|
if (!rcu_is_nocb_cpu(rdp->cpu))
|
|
return false;
|
|
__call_rcu_nocb_enqueue(rdp, rhp, &rhp->next, 1, lazy, flags);
|
|
if (__is_kfree_rcu_offset((unsigned long)rhp->func))
|
|
trace_rcu_kfree_callback(rdp->rsp->name, rhp,
|
|
(unsigned long)rhp->func,
|
|
-atomic_long_read(&rdp->nocb_q_count_lazy),
|
|
-atomic_long_read(&rdp->nocb_q_count));
|
|
else
|
|
trace_rcu_callback(rdp->rsp->name, rhp,
|
|
-atomic_long_read(&rdp->nocb_q_count_lazy),
|
|
-atomic_long_read(&rdp->nocb_q_count));
|
|
|
|
/*
|
|
* If called from an extended quiescent state with interrupts
|
|
* disabled, invoke the RCU core in order to allow the idle-entry
|
|
* deferred-wakeup check to function.
|
|
*/
|
|
if (irqs_disabled_flags(flags) &&
|
|
!rcu_is_watching() &&
|
|
cpu_online(smp_processor_id()))
|
|
invoke_rcu_core();
|
|
|
|
return true;
|
|
}
|
|
|
|
/*
|
|
* Adopt orphaned callbacks on a no-CBs CPU, or return 0 if this is
|
|
* not a no-CBs CPU.
|
|
*/
|
|
static bool __maybe_unused rcu_nocb_adopt_orphan_cbs(struct rcu_data *my_rdp,
|
|
struct rcu_data *rdp,
|
|
unsigned long flags)
|
|
{
|
|
lockdep_assert_irqs_disabled();
|
|
if (!rcu_is_nocb_cpu(smp_processor_id()))
|
|
return false; /* Not NOCBs CPU, caller must migrate CBs. */
|
|
__call_rcu_nocb_enqueue(my_rdp, rcu_segcblist_head(&rdp->cblist),
|
|
rcu_segcblist_tail(&rdp->cblist),
|
|
rcu_segcblist_n_cbs(&rdp->cblist),
|
|
rcu_segcblist_n_lazy_cbs(&rdp->cblist), flags);
|
|
rcu_segcblist_init(&rdp->cblist);
|
|
rcu_segcblist_disable(&rdp->cblist);
|
|
return true;
|
|
}
|
|
|
|
/*
|
|
* If necessary, kick off a new grace period, and either way wait
|
|
* for a subsequent grace period to complete.
|
|
*/
|
|
static void rcu_nocb_wait_gp(struct rcu_data *rdp)
|
|
{
|
|
unsigned long c;
|
|
bool d;
|
|
unsigned long flags;
|
|
bool needwake;
|
|
struct rcu_node *rnp = rdp->mynode;
|
|
|
|
raw_spin_lock_irqsave_rcu_node(rnp, flags);
|
|
needwake = rcu_start_future_gp(rnp, rdp, &c);
|
|
raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
|
|
if (needwake)
|
|
rcu_gp_kthread_wake(rdp->rsp);
|
|
|
|
/*
|
|
* Wait for the grace period. Do so interruptibly to avoid messing
|
|
* up the load average.
|
|
*/
|
|
trace_rcu_future_gp(rnp, rdp, c, TPS("StartWait"));
|
|
for (;;) {
|
|
swait_event_interruptible(
|
|
rnp->nocb_gp_wq[c & 0x1],
|
|
(d = ULONG_CMP_GE(READ_ONCE(rnp->completed), c)));
|
|
if (likely(d))
|
|
break;
|
|
WARN_ON(signal_pending(current));
|
|
trace_rcu_future_gp(rnp, rdp, c, TPS("ResumeWait"));
|
|
}
|
|
trace_rcu_future_gp(rnp, rdp, c, TPS("EndWait"));
|
|
smp_mb(); /* Ensure that CB invocation happens after GP end. */
|
|
}
|
|
|
|
/*
|
|
* Leaders come here to wait for additional callbacks to show up.
|
|
* This function does not return until callbacks appear.
|
|
*/
|
|
static void nocb_leader_wait(struct rcu_data *my_rdp)
|
|
{
|
|
bool firsttime = true;
|
|
unsigned long flags;
|
|
bool gotcbs;
|
|
struct rcu_data *rdp;
|
|
struct rcu_head **tail;
|
|
|
|
wait_again:
|
|
|
|
/* Wait for callbacks to appear. */
|
|
if (!rcu_nocb_poll) {
|
|
trace_rcu_nocb_wake(my_rdp->rsp->name, my_rdp->cpu, TPS("Sleep"));
|
|
swait_event_interruptible(my_rdp->nocb_wq,
|
|
!READ_ONCE(my_rdp->nocb_leader_sleep));
|
|
raw_spin_lock_irqsave(&my_rdp->nocb_lock, flags);
|
|
my_rdp->nocb_leader_sleep = true;
|
|
WRITE_ONCE(my_rdp->nocb_defer_wakeup, RCU_NOCB_WAKE_NOT);
|
|
del_timer(&my_rdp->nocb_timer);
|
|
raw_spin_unlock_irqrestore(&my_rdp->nocb_lock, flags);
|
|
} else if (firsttime) {
|
|
firsttime = false; /* Don't drown trace log with "Poll"! */
|
|
trace_rcu_nocb_wake(my_rdp->rsp->name, my_rdp->cpu, TPS("Poll"));
|
|
}
|
|
|
|
/*
|
|
* Each pass through the following loop checks a follower for CBs.
|
|
* We are our own first follower. Any CBs found are moved to
|
|
* nocb_gp_head, where they await a grace period.
|
|
*/
|
|
gotcbs = false;
|
|
smp_mb(); /* wakeup and _sleep before ->nocb_head reads. */
|
|
for (rdp = my_rdp; rdp; rdp = rdp->nocb_next_follower) {
|
|
rdp->nocb_gp_head = READ_ONCE(rdp->nocb_head);
|
|
if (!rdp->nocb_gp_head)
|
|
continue; /* No CBs here, try next follower. */
|
|
|
|
/* Move callbacks to wait-for-GP list, which is empty. */
|
|
WRITE_ONCE(rdp->nocb_head, NULL);
|
|
rdp->nocb_gp_tail = xchg(&rdp->nocb_tail, &rdp->nocb_head);
|
|
gotcbs = true;
|
|
}
|
|
|
|
/* No callbacks? Sleep a bit if polling, and go retry. */
|
|
if (unlikely(!gotcbs)) {
|
|
WARN_ON(signal_pending(current));
|
|
if (rcu_nocb_poll) {
|
|
schedule_timeout_interruptible(1);
|
|
} else {
|
|
trace_rcu_nocb_wake(my_rdp->rsp->name, my_rdp->cpu,
|
|
TPS("WokeEmpty"));
|
|
}
|
|
goto wait_again;
|
|
}
|
|
|
|
/* Wait for one grace period. */
|
|
rcu_nocb_wait_gp(my_rdp);
|
|
|
|
/* Each pass through the following loop wakes a follower, if needed. */
|
|
for (rdp = my_rdp; rdp; rdp = rdp->nocb_next_follower) {
|
|
if (!rcu_nocb_poll &&
|
|
READ_ONCE(rdp->nocb_head) &&
|
|
READ_ONCE(my_rdp->nocb_leader_sleep)) {
|
|
raw_spin_lock_irqsave(&my_rdp->nocb_lock, flags);
|
|
my_rdp->nocb_leader_sleep = false;/* No need to sleep.*/
|
|
raw_spin_unlock_irqrestore(&my_rdp->nocb_lock, flags);
|
|
}
|
|
if (!rdp->nocb_gp_head)
|
|
continue; /* No CBs, so no need to wake follower. */
|
|
|
|
/* Append callbacks to follower's "done" list. */
|
|
raw_spin_lock_irqsave(&rdp->nocb_lock, flags);
|
|
tail = rdp->nocb_follower_tail;
|
|
rdp->nocb_follower_tail = rdp->nocb_gp_tail;
|
|
*tail = rdp->nocb_gp_head;
|
|
raw_spin_unlock_irqrestore(&rdp->nocb_lock, flags);
|
|
if (rdp != my_rdp && tail == &rdp->nocb_follower_head) {
|
|
/* List was empty, so wake up the follower. */
|
|
swake_up(&rdp->nocb_wq);
|
|
}
|
|
}
|
|
|
|
/* If we (the leader) don't have CBs, go wait some more. */
|
|
if (!my_rdp->nocb_follower_head)
|
|
goto wait_again;
|
|
}
|
|
|
|
/*
|
|
* Followers come here to wait for additional callbacks to show up.
|
|
* This function does not return until callbacks appear.
|
|
*/
|
|
static void nocb_follower_wait(struct rcu_data *rdp)
|
|
{
|
|
for (;;) {
|
|
trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, TPS("FollowerSleep"));
|
|
swait_event_interruptible(rdp->nocb_wq,
|
|
READ_ONCE(rdp->nocb_follower_head));
|
|
if (smp_load_acquire(&rdp->nocb_follower_head)) {
|
|
/* ^^^ Ensure CB invocation follows _head test. */
|
|
return;
|
|
}
|
|
WARN_ON(signal_pending(current));
|
|
trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, TPS("WokeEmpty"));
|
|
}
|
|
}
|
|
|
|
/*
|
|
* Per-rcu_data kthread, but only for no-CBs CPUs. Each kthread invokes
|
|
* callbacks queued by the corresponding no-CBs CPU, however, there is
|
|
* an optional leader-follower relationship so that the grace-period
|
|
* kthreads don't have to do quite so many wakeups.
|
|
*/
|
|
static int rcu_nocb_kthread(void *arg)
|
|
{
|
|
int c, cl;
|
|
unsigned long flags;
|
|
struct rcu_head *list;
|
|
struct rcu_head *next;
|
|
struct rcu_head **tail;
|
|
struct rcu_data *rdp = arg;
|
|
|
|
/* Each pass through this loop invokes one batch of callbacks */
|
|
for (;;) {
|
|
/* Wait for callbacks. */
|
|
if (rdp->nocb_leader == rdp)
|
|
nocb_leader_wait(rdp);
|
|
else
|
|
nocb_follower_wait(rdp);
|
|
|
|
/* Pull the ready-to-invoke callbacks onto local list. */
|
|
raw_spin_lock_irqsave(&rdp->nocb_lock, flags);
|
|
list = rdp->nocb_follower_head;
|
|
rdp->nocb_follower_head = NULL;
|
|
tail = rdp->nocb_follower_tail;
|
|
rdp->nocb_follower_tail = &rdp->nocb_follower_head;
|
|
raw_spin_unlock_irqrestore(&rdp->nocb_lock, flags);
|
|
BUG_ON(!list);
|
|
trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, TPS("WokeNonEmpty"));
|
|
|
|
/* Each pass through the following loop invokes a callback. */
|
|
trace_rcu_batch_start(rdp->rsp->name,
|
|
atomic_long_read(&rdp->nocb_q_count_lazy),
|
|
atomic_long_read(&rdp->nocb_q_count), -1);
|
|
c = cl = 0;
|
|
while (list) {
|
|
next = list->next;
|
|
/* Wait for enqueuing to complete, if needed. */
|
|
while (next == NULL && &list->next != tail) {
|
|
trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
|
|
TPS("WaitQueue"));
|
|
schedule_timeout_interruptible(1);
|
|
trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu,
|
|
TPS("WokeQueue"));
|
|
next = list->next;
|
|
}
|
|
debug_rcu_head_unqueue(list);
|
|
local_bh_disable();
|
|
if (__rcu_reclaim(rdp->rsp->name, list))
|
|
cl++;
|
|
c++;
|
|
local_bh_enable();
|
|
cond_resched_rcu_qs();
|
|
list = next;
|
|
}
|
|
trace_rcu_batch_end(rdp->rsp->name, c, !!list, 0, 0, 1);
|
|
smp_mb__before_atomic(); /* _add after CB invocation. */
|
|
atomic_long_add(-c, &rdp->nocb_q_count);
|
|
atomic_long_add(-cl, &rdp->nocb_q_count_lazy);
|
|
rdp->n_nocbs_invoked += c;
|
|
}
|
|
return 0;
|
|
}
|
|
|
|
/* Is a deferred wakeup of rcu_nocb_kthread() required? */
|
|
static int rcu_nocb_need_deferred_wakeup(struct rcu_data *rdp)
|
|
{
|
|
return READ_ONCE(rdp->nocb_defer_wakeup);
|
|
}
|
|
|
|
/* Do a deferred wakeup of rcu_nocb_kthread(). */
|
|
static void do_nocb_deferred_wakeup_common(struct rcu_data *rdp)
|
|
{
|
|
unsigned long flags;
|
|
int ndw;
|
|
|
|
raw_spin_lock_irqsave(&rdp->nocb_lock, flags);
|
|
if (!rcu_nocb_need_deferred_wakeup(rdp)) {
|
|
raw_spin_unlock_irqrestore(&rdp->nocb_lock, flags);
|
|
return;
|
|
}
|
|
ndw = READ_ONCE(rdp->nocb_defer_wakeup);
|
|
WRITE_ONCE(rdp->nocb_defer_wakeup, RCU_NOCB_WAKE_NOT);
|
|
__wake_nocb_leader(rdp, ndw == RCU_NOCB_WAKE_FORCE, flags);
|
|
trace_rcu_nocb_wake(rdp->rsp->name, rdp->cpu, TPS("DeferredWake"));
|
|
}
|
|
|
|
/* Do a deferred wakeup of rcu_nocb_kthread() from a timer handler. */
|
|
static void do_nocb_deferred_wakeup_timer(struct timer_list *t)
|
|
{
|
|
struct rcu_data *rdp = from_timer(rdp, t, nocb_timer);
|
|
|
|
do_nocb_deferred_wakeup_common(rdp);
|
|
}
|
|
|
|
/*
|
|
* Do a deferred wakeup of rcu_nocb_kthread() from fastpath.
|
|
* This means we do an inexact common-case check. Note that if
|
|
* we miss, ->nocb_timer will eventually clean things up.
|
|
*/
|
|
static void do_nocb_deferred_wakeup(struct rcu_data *rdp)
|
|
{
|
|
if (rcu_nocb_need_deferred_wakeup(rdp))
|
|
do_nocb_deferred_wakeup_common(rdp);
|
|
}
|
|
|
|
void __init rcu_init_nohz(void)
|
|
{
|
|
int cpu;
|
|
bool need_rcu_nocb_mask = true;
|
|
struct rcu_state *rsp;
|
|
|
|
#if defined(CONFIG_NO_HZ_FULL)
|
|
if (tick_nohz_full_running && cpumask_weight(tick_nohz_full_mask))
|
|
need_rcu_nocb_mask = true;
|
|
#endif /* #if defined(CONFIG_NO_HZ_FULL) */
|
|
|
|
if (!have_rcu_nocb_mask && need_rcu_nocb_mask) {
|
|
if (!zalloc_cpumask_var(&rcu_nocb_mask, GFP_KERNEL)) {
|
|
pr_info("rcu_nocb_mask allocation failed, callback offloading disabled.\n");
|
|
return;
|
|
}
|
|
have_rcu_nocb_mask = true;
|
|
}
|
|
if (!have_rcu_nocb_mask)
|
|
return;
|
|
|
|
#if defined(CONFIG_NO_HZ_FULL)
|
|
if (tick_nohz_full_running)
|
|
cpumask_or(rcu_nocb_mask, rcu_nocb_mask, tick_nohz_full_mask);
|
|
#endif /* #if defined(CONFIG_NO_HZ_FULL) */
|
|
|
|
if (!cpumask_subset(rcu_nocb_mask, cpu_possible_mask)) {
|
|
pr_info("\tNote: kernel parameter 'rcu_nocbs=' contains nonexistent CPUs.\n");
|
|
cpumask_and(rcu_nocb_mask, cpu_possible_mask,
|
|
rcu_nocb_mask);
|
|
}
|
|
pr_info("\tOffload RCU callbacks from CPUs: %*pbl.\n",
|
|
cpumask_pr_args(rcu_nocb_mask));
|
|
if (rcu_nocb_poll)
|
|
pr_info("\tPoll for callbacks from no-CBs CPUs.\n");
|
|
|
|
for_each_rcu_flavor(rsp) {
|
|
for_each_cpu(cpu, rcu_nocb_mask)
|
|
init_nocb_callback_list(per_cpu_ptr(rsp->rda, cpu));
|
|
rcu_organize_nocb_kthreads(rsp);
|
|
}
|
|
}
|
|
|
|
/* Initialize per-rcu_data variables for no-CBs CPUs. */
|
|
static void __init rcu_boot_init_nocb_percpu_data(struct rcu_data *rdp)
|
|
{
|
|
rdp->nocb_tail = &rdp->nocb_head;
|
|
init_swait_queue_head(&rdp->nocb_wq);
|
|
rdp->nocb_follower_tail = &rdp->nocb_follower_head;
|
|
raw_spin_lock_init(&rdp->nocb_lock);
|
|
timer_setup(&rdp->nocb_timer, do_nocb_deferred_wakeup_timer, 0);
|
|
}
|
|
|
|
/*
|
|
* If the specified CPU is a no-CBs CPU that does not already have its
|
|
* rcuo kthread for the specified RCU flavor, spawn it. If the CPUs are
|
|
* brought online out of order, this can require re-organizing the
|
|
* leader-follower relationships.
|
|
*/
|
|
static void rcu_spawn_one_nocb_kthread(struct rcu_state *rsp, int cpu)
|
|
{
|
|
struct rcu_data *rdp;
|
|
struct rcu_data *rdp_last;
|
|
struct rcu_data *rdp_old_leader;
|
|
struct rcu_data *rdp_spawn = per_cpu_ptr(rsp->rda, cpu);
|
|
struct task_struct *t;
|
|
|
|
/*
|
|
* If this isn't a no-CBs CPU or if it already has an rcuo kthread,
|
|
* then nothing to do.
|
|
*/
|
|
if (!rcu_is_nocb_cpu(cpu) || rdp_spawn->nocb_kthread)
|
|
return;
|
|
|
|
/* If we didn't spawn the leader first, reorganize! */
|
|
rdp_old_leader = rdp_spawn->nocb_leader;
|
|
if (rdp_old_leader != rdp_spawn && !rdp_old_leader->nocb_kthread) {
|
|
rdp_last = NULL;
|
|
rdp = rdp_old_leader;
|
|
do {
|
|
rdp->nocb_leader = rdp_spawn;
|
|
if (rdp_last && rdp != rdp_spawn)
|
|
rdp_last->nocb_next_follower = rdp;
|
|
if (rdp == rdp_spawn) {
|
|
rdp = rdp->nocb_next_follower;
|
|
} else {
|
|
rdp_last = rdp;
|
|
rdp = rdp->nocb_next_follower;
|
|
rdp_last->nocb_next_follower = NULL;
|
|
}
|
|
} while (rdp);
|
|
rdp_spawn->nocb_next_follower = rdp_old_leader;
|
|
}
|
|
|
|
/* Spawn the kthread for this CPU and RCU flavor. */
|
|
t = kthread_run(rcu_nocb_kthread, rdp_spawn,
|
|
"rcuo%c/%d", rsp->abbr, cpu);
|
|
BUG_ON(IS_ERR(t));
|
|
WRITE_ONCE(rdp_spawn->nocb_kthread, t);
|
|
}
|
|
|
|
/*
|
|
* If the specified CPU is a no-CBs CPU that does not already have its
|
|
* rcuo kthreads, spawn them.
|
|
*/
|
|
static void rcu_spawn_all_nocb_kthreads(int cpu)
|
|
{
|
|
struct rcu_state *rsp;
|
|
|
|
if (rcu_scheduler_fully_active)
|
|
for_each_rcu_flavor(rsp)
|
|
rcu_spawn_one_nocb_kthread(rsp, cpu);
|
|
}
|
|
|
|
/*
|
|
* Once the scheduler is running, spawn rcuo kthreads for all online
|
|
* no-CBs CPUs. This assumes that the early_initcall()s happen before
|
|
* non-boot CPUs come online -- if this changes, we will need to add
|
|
* some mutual exclusion.
|
|
*/
|
|
static void __init rcu_spawn_nocb_kthreads(void)
|
|
{
|
|
int cpu;
|
|
|
|
for_each_online_cpu(cpu)
|
|
rcu_spawn_all_nocb_kthreads(cpu);
|
|
}
|
|
|
|
/* How many follower CPU IDs per leader? Default of -1 for sqrt(nr_cpu_ids). */
|
|
static int rcu_nocb_leader_stride = -1;
|
|
module_param(rcu_nocb_leader_stride, int, 0444);
|
|
|
|
/*
|
|
* Initialize leader-follower relationships for all no-CBs CPU.
|
|
*/
|
|
static void __init rcu_organize_nocb_kthreads(struct rcu_state *rsp)
|
|
{
|
|
int cpu;
|
|
int ls = rcu_nocb_leader_stride;
|
|
int nl = 0; /* Next leader. */
|
|
struct rcu_data *rdp;
|
|
struct rcu_data *rdp_leader = NULL; /* Suppress misguided gcc warn. */
|
|
struct rcu_data *rdp_prev = NULL;
|
|
|
|
if (!have_rcu_nocb_mask)
|
|
return;
|
|
if (ls == -1) {
|
|
ls = int_sqrt(nr_cpu_ids);
|
|
rcu_nocb_leader_stride = ls;
|
|
}
|
|
|
|
/*
|
|
* Each pass through this loop sets up one rcu_data structure.
|
|
* Should the corresponding CPU come online in the future, then
|
|
* we will spawn the needed set of rcu_nocb_kthread() kthreads.
|
|
*/
|
|
for_each_cpu(cpu, rcu_nocb_mask) {
|
|
rdp = per_cpu_ptr(rsp->rda, cpu);
|
|
if (rdp->cpu >= nl) {
|
|
/* New leader, set up for followers & next leader. */
|
|
nl = DIV_ROUND_UP(rdp->cpu + 1, ls) * ls;
|
|
rdp->nocb_leader = rdp;
|
|
rdp_leader = rdp;
|
|
} else {
|
|
/* Another follower, link to previous leader. */
|
|
rdp->nocb_leader = rdp_leader;
|
|
rdp_prev->nocb_next_follower = rdp;
|
|
}
|
|
rdp_prev = rdp;
|
|
}
|
|
}
|
|
|
|
/* Prevent __call_rcu() from enqueuing callbacks on no-CBs CPUs */
|
|
static bool init_nocb_callback_list(struct rcu_data *rdp)
|
|
{
|
|
if (!rcu_is_nocb_cpu(rdp->cpu))
|
|
return false;
|
|
|
|
/* If there are early-boot callbacks, move them to nocb lists. */
|
|
if (!rcu_segcblist_empty(&rdp->cblist)) {
|
|
rdp->nocb_head = rcu_segcblist_head(&rdp->cblist);
|
|
rdp->nocb_tail = rcu_segcblist_tail(&rdp->cblist);
|
|
atomic_long_set(&rdp->nocb_q_count,
|
|
rcu_segcblist_n_cbs(&rdp->cblist));
|
|
atomic_long_set(&rdp->nocb_q_count_lazy,
|
|
rcu_segcblist_n_lazy_cbs(&rdp->cblist));
|
|
rcu_segcblist_init(&rdp->cblist);
|
|
}
|
|
rcu_segcblist_disable(&rdp->cblist);
|
|
return true;
|
|
}
|
|
|
|
#else /* #ifdef CONFIG_RCU_NOCB_CPU */
|
|
|
|
static bool rcu_nocb_cpu_needs_barrier(struct rcu_state *rsp, int cpu)
|
|
{
|
|
WARN_ON_ONCE(1); /* Should be dead code. */
|
|
return false;
|
|
}
|
|
|
|
static void rcu_nocb_gp_cleanup(struct swait_queue_head *sq)
|
|
{
|
|
}
|
|
|
|
static void rcu_nocb_gp_set(struct rcu_node *rnp, int nrq)
|
|
{
|
|
}
|
|
|
|
static struct swait_queue_head *rcu_nocb_gp_get(struct rcu_node *rnp)
|
|
{
|
|
return NULL;
|
|
}
|
|
|
|
static void rcu_init_one_nocb(struct rcu_node *rnp)
|
|
{
|
|
}
|
|
|
|
static bool __call_rcu_nocb(struct rcu_data *rdp, struct rcu_head *rhp,
|
|
bool lazy, unsigned long flags)
|
|
{
|
|
return false;
|
|
}
|
|
|
|
static bool __maybe_unused rcu_nocb_adopt_orphan_cbs(struct rcu_data *my_rdp,
|
|
struct rcu_data *rdp,
|
|
unsigned long flags)
|
|
{
|
|
return false;
|
|
}
|
|
|
|
static void __init rcu_boot_init_nocb_percpu_data(struct rcu_data *rdp)
|
|
{
|
|
}
|
|
|
|
static int rcu_nocb_need_deferred_wakeup(struct rcu_data *rdp)
|
|
{
|
|
return false;
|
|
}
|
|
|
|
static void do_nocb_deferred_wakeup(struct rcu_data *rdp)
|
|
{
|
|
}
|
|
|
|
static void rcu_spawn_all_nocb_kthreads(int cpu)
|
|
{
|
|
}
|
|
|
|
static void __init rcu_spawn_nocb_kthreads(void)
|
|
{
|
|
}
|
|
|
|
static bool init_nocb_callback_list(struct rcu_data *rdp)
|
|
{
|
|
return false;
|
|
}
|
|
|
|
#endif /* #else #ifdef CONFIG_RCU_NOCB_CPU */
|
|
|
|
/*
|
|
* An adaptive-ticks CPU can potentially execute in kernel mode for an
|
|
* arbitrarily long period of time with the scheduling-clock tick turned
|
|
* off. RCU will be paying attention to this CPU because it is in the
|
|
* kernel, but the CPU cannot be guaranteed to be executing the RCU state
|
|
* machine because the scheduling-clock tick has been disabled. Therefore,
|
|
* if an adaptive-ticks CPU is failing to respond to the current grace
|
|
* period and has not be idle from an RCU perspective, kick it.
|
|
*/
|
|
static void __maybe_unused rcu_kick_nohz_cpu(int cpu)
|
|
{
|
|
#ifdef CONFIG_NO_HZ_FULL
|
|
if (tick_nohz_full_cpu(cpu))
|
|
smp_send_reschedule(cpu);
|
|
#endif /* #ifdef CONFIG_NO_HZ_FULL */
|
|
}
|
|
|
|
/*
|
|
* Is this CPU a NO_HZ_FULL CPU that should ignore RCU so that the
|
|
* grace-period kthread will do force_quiescent_state() processing?
|
|
* The idea is to avoid waking up RCU core processing on such a
|
|
* CPU unless the grace period has extended for too long.
|
|
*
|
|
* This code relies on the fact that all NO_HZ_FULL CPUs are also
|
|
* CONFIG_RCU_NOCB_CPU CPUs.
|
|
*/
|
|
static bool rcu_nohz_full_cpu(struct rcu_state *rsp)
|
|
{
|
|
#ifdef CONFIG_NO_HZ_FULL
|
|
if (tick_nohz_full_cpu(smp_processor_id()) &&
|
|
(!rcu_gp_in_progress(rsp) ||
|
|
ULONG_CMP_LT(jiffies, READ_ONCE(rsp->gp_start) + HZ)))
|
|
return true;
|
|
#endif /* #ifdef CONFIG_NO_HZ_FULL */
|
|
return false;
|
|
}
|
|
|
|
/*
|
|
* Bind the grace-period kthread for the sysidle flavor of RCU to the
|
|
* timekeeping CPU.
|
|
*/
|
|
static void rcu_bind_gp_kthread(void)
|
|
{
|
|
int __maybe_unused cpu;
|
|
|
|
if (!tick_nohz_full_enabled())
|
|
return;
|
|
housekeeping_affine(current, HK_FLAG_RCU);
|
|
}
|
|
|
|
/* Record the current task on dyntick-idle entry. */
|
|
static void rcu_dynticks_task_enter(void)
|
|
{
|
|
#if defined(CONFIG_TASKS_RCU) && defined(CONFIG_NO_HZ_FULL)
|
|
WRITE_ONCE(current->rcu_tasks_idle_cpu, smp_processor_id());
|
|
#endif /* #if defined(CONFIG_TASKS_RCU) && defined(CONFIG_NO_HZ_FULL) */
|
|
}
|
|
|
|
/* Record no current task on dyntick-idle exit. */
|
|
static void rcu_dynticks_task_exit(void)
|
|
{
|
|
#if defined(CONFIG_TASKS_RCU) && defined(CONFIG_NO_HZ_FULL)
|
|
WRITE_ONCE(current->rcu_tasks_idle_cpu, -1);
|
|
#endif /* #if defined(CONFIG_TASKS_RCU) && defined(CONFIG_NO_HZ_FULL) */
|
|
}
|