![Paul E. McKenney](/assets/img/avatar_default.png)
Combine the duplicate definitions of ULONG_CMP_GE(), ULONG_CMP_LT(), and rcu_preempt_depth() into include/linux/rcupdate.h. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
612 lines
19 KiB
C
612 lines
19 KiB
C
/*
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* Read-Copy Update mechanism for mutual exclusion, the Bloatwatch edition
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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, write to the Free Software
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* Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
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*
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* Copyright (c) 2010 Linaro
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*
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* Author: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
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*/
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#ifdef CONFIG_TINY_PREEMPT_RCU
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#include <linux/delay.h>
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/* Global control variables for preemptible RCU. */
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struct rcu_preempt_ctrlblk {
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struct rcu_ctrlblk rcb; /* curtail: ->next ptr of last CB for GP. */
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struct rcu_head **nexttail;
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/* Tasks blocked in a preemptible RCU */
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/* read-side critical section while an */
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/* preemptible-RCU grace period is in */
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/* progress must wait for a later grace */
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/* period. This pointer points to the */
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/* ->next pointer of the last task that */
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/* must wait for a later grace period, or */
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/* to &->rcb.rcucblist if there is no */
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/* such task. */
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struct list_head blkd_tasks;
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/* Tasks blocked in RCU read-side critical */
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/* section. Tasks are placed at the head */
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/* of this list and age towards the tail. */
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struct list_head *gp_tasks;
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/* Pointer to the first task blocking the */
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/* current grace period, or NULL if there */
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/* is not such task. */
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struct list_head *exp_tasks;
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/* Pointer to first task blocking the */
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/* current expedited grace period, or NULL */
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/* if there is no such task. If there */
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/* is no current expedited grace period, */
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/* then there cannot be any such task. */
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u8 gpnum; /* Current grace period. */
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u8 gpcpu; /* Last grace period blocked by the CPU. */
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u8 completed; /* Last grace period completed. */
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/* If all three are equal, RCU is idle. */
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};
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static struct rcu_preempt_ctrlblk rcu_preempt_ctrlblk = {
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.rcb.donetail = &rcu_preempt_ctrlblk.rcb.rcucblist,
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.rcb.curtail = &rcu_preempt_ctrlblk.rcb.rcucblist,
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.nexttail = &rcu_preempt_ctrlblk.rcb.rcucblist,
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.blkd_tasks = LIST_HEAD_INIT(rcu_preempt_ctrlblk.blkd_tasks),
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};
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static int rcu_preempted_readers_exp(void);
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static void rcu_report_exp_done(void);
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/*
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* Return true if the CPU has not yet responded to the current grace period.
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*/
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static int rcu_cpu_cur_gp(void)
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{
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return rcu_preempt_ctrlblk.gpcpu != rcu_preempt_ctrlblk.gpnum;
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}
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/*
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* Check for a running RCU reader. Because there is only one CPU,
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* there can be but one running RCU reader at a time. ;-)
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*/
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static int rcu_preempt_running_reader(void)
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{
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return current->rcu_read_lock_nesting;
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}
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/*
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* Check for preempted RCU readers blocking any grace period.
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* If the caller needs a reliable answer, it must disable hard irqs.
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*/
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static int rcu_preempt_blocked_readers_any(void)
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{
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return !list_empty(&rcu_preempt_ctrlblk.blkd_tasks);
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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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* If the caller needs a reliable answer, it must disable hard irqs.
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*/
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static int rcu_preempt_blocked_readers_cgp(void)
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{
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return rcu_preempt_ctrlblk.gp_tasks != NULL;
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}
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/*
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* Return true if another preemptible-RCU grace period is needed.
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*/
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static int rcu_preempt_needs_another_gp(void)
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{
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return *rcu_preempt_ctrlblk.rcb.curtail != NULL;
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}
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/*
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* Return true if a preemptible-RCU grace period is in progress.
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* The caller must disable hardirqs.
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*/
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static int rcu_preempt_gp_in_progress(void)
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{
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return rcu_preempt_ctrlblk.completed != rcu_preempt_ctrlblk.gpnum;
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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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* 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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* Unlike the other rcu_*_qs() functions, callers to this function
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* must disable irqs in order to protect the assignment to
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* ->rcu_read_unlock_special.
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*
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* Because this is a single-CPU implementation, the only way a grace
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* period can end is if the CPU is in a quiescent state. The reason is
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* that a blocked preemptible-RCU reader can exit its critical section
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* only if the CPU is running it at the time. Therefore, when the
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* last task blocking the current grace period exits its RCU read-side
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* critical section, neither the CPU nor blocked tasks will be stopping
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* the current grace period. (In contrast, SMP implementations
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* might have CPUs running in RCU read-side critical sections that
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* block later grace periods -- but this is not possible given only
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* one CPU.)
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*/
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static void rcu_preempt_cpu_qs(void)
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{
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/* Record both CPU and task as having responded to current GP. */
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rcu_preempt_ctrlblk.gpcpu = rcu_preempt_ctrlblk.gpnum;
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current->rcu_read_unlock_special &= ~RCU_READ_UNLOCK_NEED_QS;
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/*
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* If there is no GP, or if blocked readers are still blocking GP,
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* then there is nothing more to do.
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*/
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if (!rcu_preempt_gp_in_progress() || rcu_preempt_blocked_readers_cgp())
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return;
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/* Advance callbacks. */
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rcu_preempt_ctrlblk.completed = rcu_preempt_ctrlblk.gpnum;
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rcu_preempt_ctrlblk.rcb.donetail = rcu_preempt_ctrlblk.rcb.curtail;
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rcu_preempt_ctrlblk.rcb.curtail = rcu_preempt_ctrlblk.nexttail;
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/* If there are no blocked readers, next GP is done instantly. */
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if (!rcu_preempt_blocked_readers_any())
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rcu_preempt_ctrlblk.rcb.donetail = rcu_preempt_ctrlblk.nexttail;
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/* If there are done callbacks, make RCU_SOFTIRQ process them. */
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if (*rcu_preempt_ctrlblk.rcb.donetail != NULL)
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raise_softirq(RCU_SOFTIRQ);
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}
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/*
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* Start a new RCU grace period if warranted. Hard irqs must be disabled.
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*/
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static void rcu_preempt_start_gp(void)
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{
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if (!rcu_preempt_gp_in_progress() && rcu_preempt_needs_another_gp()) {
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/* Official start of GP. */
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rcu_preempt_ctrlblk.gpnum++;
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/* Any blocked RCU readers block new GP. */
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if (rcu_preempt_blocked_readers_any())
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rcu_preempt_ctrlblk.gp_tasks =
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rcu_preempt_ctrlblk.blkd_tasks.next;
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/* If there is no running reader, CPU is done with GP. */
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if (!rcu_preempt_running_reader())
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rcu_preempt_cpu_qs();
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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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* If the task started after the current grace period began, as recorded
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* by ->gpcpu, we enqueue at the beginning of the list. Otherwise
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* before the element referenced by ->gp_tasks (or at the tail if
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* ->gp_tasks is NULL) and point ->gp_tasks at the newly added element.
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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 ->gp_tasks pointer becomes
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* NULL.
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*
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* Caller must disable preemption.
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*/
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void rcu_preempt_note_context_switch(void)
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{
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struct task_struct *t = current;
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unsigned long flags;
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local_irq_save(flags); /* must exclude scheduler_tick(). */
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if (rcu_preempt_running_reader() &&
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(t->rcu_read_unlock_special & RCU_READ_UNLOCK_BLOCKED) == 0) {
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/* Possibly blocking in an RCU read-side critical section. */
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t->rcu_read_unlock_special |= RCU_READ_UNLOCK_BLOCKED;
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/*
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* If this CPU has already checked in, then this task
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* will hold up the next grace period rather than the
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* current grace period. Queue the task accordingly.
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* If the task is queued for the current grace period
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* (i.e., this CPU has not yet passed through a quiescent
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* state for the current grace period), then as long
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* as that task remains queued, the current grace period
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* cannot end.
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*/
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list_add(&t->rcu_node_entry, &rcu_preempt_ctrlblk.blkd_tasks);
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if (rcu_cpu_cur_gp())
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rcu_preempt_ctrlblk.gp_tasks = &t->rcu_node_entry;
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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 current grace period continues to be blocked.
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*/
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rcu_preempt_cpu_qs();
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local_irq_restore(flags);
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}
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/*
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* Tiny-preemptible RCU implementation for rcu_read_lock().
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* Just increment ->rcu_read_lock_nesting, shared state will be updated
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* if we block.
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*/
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void __rcu_read_lock(void)
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{
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current->rcu_read_lock_nesting++;
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barrier(); /* needed if we ever invoke rcu_read_lock in rcutiny.c */
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}
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EXPORT_SYMBOL_GPL(__rcu_read_lock);
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/*
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* Handle special cases during rcu_read_unlock(), such as needing to
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* notify RCU core processing or task having blocked during the RCU
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* read-side critical section.
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*/
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static void rcu_read_unlock_special(struct task_struct *t)
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{
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int empty;
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int empty_exp;
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unsigned long flags;
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struct list_head *np;
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int special;
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/*
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* NMI handlers cannot block and cannot safely manipulate state.
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* They therefore cannot possibly be special, so just leave.
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*/
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if (in_nmi())
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return;
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local_irq_save(flags);
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/*
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* If RCU core is waiting for this CPU to exit critical section,
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* let it know that we have done so.
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*/
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special = t->rcu_read_unlock_special;
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if (special & RCU_READ_UNLOCK_NEED_QS)
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rcu_preempt_cpu_qs();
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/* Hardware IRQ handlers cannot block. */
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if (in_irq()) {
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local_irq_restore(flags);
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return;
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}
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/* Clean up if blocked during RCU read-side critical section. */
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if (special & RCU_READ_UNLOCK_BLOCKED) {
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t->rcu_read_unlock_special &= ~RCU_READ_UNLOCK_BLOCKED;
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/*
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* Remove this task from the ->blkd_tasks list and adjust
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* any pointers that might have been referencing it.
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*/
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empty = !rcu_preempt_blocked_readers_cgp();
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empty_exp = rcu_preempt_ctrlblk.exp_tasks == NULL;
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np = t->rcu_node_entry.next;
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if (np == &rcu_preempt_ctrlblk.blkd_tasks)
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np = NULL;
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list_del(&t->rcu_node_entry);
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if (&t->rcu_node_entry == rcu_preempt_ctrlblk.gp_tasks)
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rcu_preempt_ctrlblk.gp_tasks = np;
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if (&t->rcu_node_entry == rcu_preempt_ctrlblk.exp_tasks)
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rcu_preempt_ctrlblk.exp_tasks = np;
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INIT_LIST_HEAD(&t->rcu_node_entry);
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/*
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* If this was the last task on the current list, and if
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* we aren't waiting on the CPU, report the quiescent state
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* and start a new grace period if needed.
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*/
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if (!empty && !rcu_preempt_blocked_readers_cgp()) {
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rcu_preempt_cpu_qs();
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rcu_preempt_start_gp();
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}
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/*
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* If this was the last task on the expedited lists,
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* then we need wake up the waiting task.
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*/
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if (!empty_exp && rcu_preempt_ctrlblk.exp_tasks == NULL)
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rcu_report_exp_done();
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}
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local_irq_restore(flags);
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}
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/*
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* Tiny-preemptible RCU implementation for rcu_read_unlock().
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* Decrement ->rcu_read_lock_nesting. If the result is zero (outermost
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* rcu_read_unlock()) and ->rcu_read_unlock_special is non-zero, then
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* invoke rcu_read_unlock_special() to clean up after a context switch
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* in an RCU read-side critical section and other special cases.
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*/
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void __rcu_read_unlock(void)
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{
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struct task_struct *t = current;
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barrier(); /* needed if we ever invoke rcu_read_unlock in rcutiny.c */
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--t->rcu_read_lock_nesting;
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barrier(); /* decrement before load of ->rcu_read_unlock_special */
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if (t->rcu_read_lock_nesting == 0 &&
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unlikely(ACCESS_ONCE(t->rcu_read_unlock_special)))
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rcu_read_unlock_special(t);
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#ifdef CONFIG_PROVE_LOCKING
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WARN_ON_ONCE(t->rcu_read_lock_nesting < 0);
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#endif /* #ifdef CONFIG_PROVE_LOCKING */
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}
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EXPORT_SYMBOL_GPL(__rcu_read_unlock);
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/*
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* Check for a quiescent state from the current CPU. When a task blocks,
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* the task is recorded in the rcu_preempt_ctrlblk structure, which is
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* checked elsewhere. This is called from the scheduling-clock interrupt.
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*
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* Caller must disable hard irqs.
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*/
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static void rcu_preempt_check_callbacks(void)
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{
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struct task_struct *t = current;
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if (!rcu_preempt_running_reader() && rcu_preempt_gp_in_progress())
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rcu_preempt_cpu_qs();
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if (&rcu_preempt_ctrlblk.rcb.rcucblist !=
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rcu_preempt_ctrlblk.rcb.donetail)
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raise_softirq(RCU_SOFTIRQ);
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if (rcu_preempt_gp_in_progress() && rcu_preempt_running_reader())
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t->rcu_read_unlock_special |= RCU_READ_UNLOCK_NEED_QS;
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}
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/*
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* TINY_PREEMPT_RCU has an extra callback-list tail pointer to
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* update, so this is invoked from __rcu_process_callbacks() to
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* handle that case. Of course, it is invoked for all flavors of
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* RCU, but RCU callbacks can appear only on one of the lists, and
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* neither ->nexttail nor ->donetail can possibly be NULL, so there
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* is no need for an explicit check.
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*/
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static void rcu_preempt_remove_callbacks(struct rcu_ctrlblk *rcp)
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{
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if (rcu_preempt_ctrlblk.nexttail == rcp->donetail)
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rcu_preempt_ctrlblk.nexttail = &rcp->rcucblist;
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}
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/*
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* Process callbacks for preemptible RCU.
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*/
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static void rcu_preempt_process_callbacks(void)
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{
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__rcu_process_callbacks(&rcu_preempt_ctrlblk.rcb);
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}
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/*
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* Queue a preemptible -RCU callback for invocation after a grace period.
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*/
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void call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu))
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{
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unsigned long flags;
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debug_rcu_head_queue(head);
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head->func = func;
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head->next = NULL;
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local_irq_save(flags);
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*rcu_preempt_ctrlblk.nexttail = head;
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rcu_preempt_ctrlblk.nexttail = &head->next;
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rcu_preempt_start_gp(); /* checks to see if GP needed. */
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local_irq_restore(flags);
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}
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EXPORT_SYMBOL_GPL(call_rcu);
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void rcu_barrier(void)
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{
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struct rcu_synchronize rcu;
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init_rcu_head_on_stack(&rcu.head);
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init_completion(&rcu.completion);
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/* Will wake me after RCU finished. */
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call_rcu(&rcu.head, wakeme_after_rcu);
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/* Wait for it. */
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wait_for_completion(&rcu.completion);
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destroy_rcu_head_on_stack(&rcu.head);
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}
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EXPORT_SYMBOL_GPL(rcu_barrier);
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/*
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* synchronize_rcu - wait until a grace period has elapsed.
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*
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* Control will return to the caller some time after a full grace
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* period has elapsed, in other words after all currently executing RCU
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* read-side critical sections have completed. RCU read-side critical
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* sections are delimited by rcu_read_lock() and rcu_read_unlock(),
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* and may be nested.
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*/
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void synchronize_rcu(void)
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{
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#ifdef CONFIG_DEBUG_LOCK_ALLOC
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if (!rcu_scheduler_active)
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return;
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#endif /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
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WARN_ON_ONCE(rcu_preempt_running_reader());
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if (!rcu_preempt_blocked_readers_any())
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return;
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/* Once we get past the fastpath checks, same code as rcu_barrier(). */
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rcu_barrier();
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}
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EXPORT_SYMBOL_GPL(synchronize_rcu);
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static DECLARE_WAIT_QUEUE_HEAD(sync_rcu_preempt_exp_wq);
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static unsigned long sync_rcu_preempt_exp_count;
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static DEFINE_MUTEX(sync_rcu_preempt_exp_mutex);
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/*
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* Return non-zero if there are any tasks in RCU read-side critical
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* sections blocking the current preemptible-RCU expedited grace period.
|
|
* If there is no preemptible-RCU expedited grace period currently in
|
|
* progress, returns zero unconditionally.
|
|
*/
|
|
static int rcu_preempted_readers_exp(void)
|
|
{
|
|
return rcu_preempt_ctrlblk.exp_tasks != NULL;
|
|
}
|
|
|
|
/*
|
|
* Report the exit from RCU read-side critical section for the last task
|
|
* that queued itself during or before the current expedited preemptible-RCU
|
|
* grace period.
|
|
*/
|
|
static void rcu_report_exp_done(void)
|
|
{
|
|
wake_up(&sync_rcu_preempt_exp_wq);
|
|
}
|
|
|
|
/*
|
|
* Wait for an rcu-preempt grace period, but expedite it. The basic idea
|
|
* is to rely in the fact that there is but one CPU, and that it is
|
|
* illegal for a task to invoke synchronize_rcu_expedited() while in a
|
|
* preemptible-RCU read-side critical section. Therefore, any such
|
|
* critical sections must correspond to blocked tasks, which must therefore
|
|
* be on the ->blkd_tasks list. So just record the current head of the
|
|
* list in the ->exp_tasks pointer, and wait for all tasks including and
|
|
* after the task pointed to by ->exp_tasks to drain.
|
|
*/
|
|
void synchronize_rcu_expedited(void)
|
|
{
|
|
unsigned long flags;
|
|
struct rcu_preempt_ctrlblk *rpcp = &rcu_preempt_ctrlblk;
|
|
unsigned long snap;
|
|
|
|
barrier(); /* ensure prior action seen before grace period. */
|
|
|
|
WARN_ON_ONCE(rcu_preempt_running_reader());
|
|
|
|
/*
|
|
* Acquire lock so that there is only one preemptible RCU grace
|
|
* period in flight. Of course, if someone does the expedited
|
|
* grace period for us while we are acquiring the lock, just leave.
|
|
*/
|
|
snap = sync_rcu_preempt_exp_count + 1;
|
|
mutex_lock(&sync_rcu_preempt_exp_mutex);
|
|
if (ULONG_CMP_LT(snap, sync_rcu_preempt_exp_count))
|
|
goto unlock_mb_ret; /* Others did our work for us. */
|
|
|
|
local_irq_save(flags);
|
|
|
|
/*
|
|
* All RCU readers have to already be on blkd_tasks because
|
|
* we cannot legally be executing in an RCU read-side critical
|
|
* section.
|
|
*/
|
|
|
|
/* Snapshot current head of ->blkd_tasks list. */
|
|
rpcp->exp_tasks = rpcp->blkd_tasks.next;
|
|
if (rpcp->exp_tasks == &rpcp->blkd_tasks)
|
|
rpcp->exp_tasks = NULL;
|
|
local_irq_restore(flags);
|
|
|
|
/* Wait for tail of ->blkd_tasks list to drain. */
|
|
if (rcu_preempted_readers_exp())
|
|
wait_event(sync_rcu_preempt_exp_wq,
|
|
!rcu_preempted_readers_exp());
|
|
|
|
/* Clean up and exit. */
|
|
barrier(); /* ensure expedited GP seen before counter increment. */
|
|
sync_rcu_preempt_exp_count++;
|
|
unlock_mb_ret:
|
|
mutex_unlock(&sync_rcu_preempt_exp_mutex);
|
|
barrier(); /* ensure subsequent action seen after grace period. */
|
|
}
|
|
EXPORT_SYMBOL_GPL(synchronize_rcu_expedited);
|
|
|
|
/*
|
|
* Does preemptible RCU need the CPU to stay out of dynticks mode?
|
|
*/
|
|
int rcu_preempt_needs_cpu(void)
|
|
{
|
|
if (!rcu_preempt_running_reader())
|
|
rcu_preempt_cpu_qs();
|
|
return rcu_preempt_ctrlblk.rcb.rcucblist != NULL;
|
|
}
|
|
|
|
/*
|
|
* 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 (t->rcu_read_lock_nesting == 0)
|
|
return;
|
|
t->rcu_read_lock_nesting = 1;
|
|
rcu_read_unlock();
|
|
}
|
|
|
|
#else /* #ifdef CONFIG_TINY_PREEMPT_RCU */
|
|
|
|
/*
|
|
* 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, it never has any callbacks
|
|
* to remove.
|
|
*/
|
|
static void rcu_preempt_remove_callbacks(struct rcu_ctrlblk *rcp)
|
|
{
|
|
}
|
|
|
|
/*
|
|
* Because preemptible RCU does not exist, it never has any callbacks
|
|
* to process.
|
|
*/
|
|
static void rcu_preempt_process_callbacks(void)
|
|
{
|
|
}
|
|
|
|
#endif /* #else #ifdef CONFIG_TINY_PREEMPT_RCU */
|
|
|
|
#ifdef CONFIG_DEBUG_LOCK_ALLOC
|
|
|
|
#include <linux/kernel_stat.h>
|
|
|
|
/*
|
|
* During boot, we forgive RCU lockdep issues. After this function is
|
|
* invoked, we start taking RCU lockdep issues seriously.
|
|
*/
|
|
void rcu_scheduler_starting(void)
|
|
{
|
|
WARN_ON(nr_context_switches() > 0);
|
|
rcu_scheduler_active = 1;
|
|
}
|
|
|
|
#endif /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
|