![Frederic Weisbecker](/assets/img/avatar_default.png)
Create a new subsystem that probes on kernel boundaries to keep track of the transitions between level contexts with two basic initial contexts: user or kernel. This is an abstraction of some RCU code that use such tracking to implement its userspace extended quiescent state. We need to pull this up from RCU into this new level of indirection because this tracking is also going to be used to implement an "on demand" generic virtual cputime accounting. A necessary step to shutdown the tick while still accounting the cputime. Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: H. Peter Anvin <hpa@zytor.com> Cc: Ingo Molnar <mingo@kernel.org> Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Steven Rostedt <rostedt@goodmis.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Li Zhong <zhong@linux.vnet.ibm.com> Cc: Gilad Ben-Yossef <gilad@benyossef.com> Reviewed-by: Steven Rostedt <rostedt@goodmis.org> [ paulmck: fix whitespace error and email address. ] Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
996 lines
36 KiB
C
996 lines
36 KiB
C
/*
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* Read-Copy Update mechanism for mutual exclusion
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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 IBM Corporation, 2001
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*
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* Author: Dipankar Sarma <dipankar@in.ibm.com>
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*
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* Based on the original work by Paul McKenney <paulmck@us.ibm.com>
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* and inputs from Rusty Russell, Andrea Arcangeli and Andi Kleen.
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* Papers:
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* http://www.rdrop.com/users/paulmck/paper/rclockpdcsproof.pdf
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* http://lse.sourceforge.net/locking/rclock_OLS.2001.05.01c.sc.pdf (OLS2001)
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*
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* For detailed explanation of Read-Copy Update mechanism see -
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* http://lse.sourceforge.net/locking/rcupdate.html
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*
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*/
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#ifndef __LINUX_RCUPDATE_H
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#define __LINUX_RCUPDATE_H
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#include <linux/types.h>
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#include <linux/cache.h>
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#include <linux/spinlock.h>
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#include <linux/threads.h>
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#include <linux/cpumask.h>
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#include <linux/seqlock.h>
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#include <linux/lockdep.h>
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#include <linux/completion.h>
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#include <linux/debugobjects.h>
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#include <linux/bug.h>
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#include <linux/compiler.h>
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#ifdef CONFIG_RCU_TORTURE_TEST
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extern int rcutorture_runnable; /* for sysctl */
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#endif /* #ifdef CONFIG_RCU_TORTURE_TEST */
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#if defined(CONFIG_TREE_RCU) || defined(CONFIG_TREE_PREEMPT_RCU)
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extern void rcutorture_record_test_transition(void);
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extern void rcutorture_record_progress(unsigned long vernum);
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extern void do_trace_rcu_torture_read(char *rcutorturename,
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struct rcu_head *rhp);
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#else
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static inline void rcutorture_record_test_transition(void)
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{
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}
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static inline void rcutorture_record_progress(unsigned long vernum)
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{
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}
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#ifdef CONFIG_RCU_TRACE
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extern void do_trace_rcu_torture_read(char *rcutorturename,
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struct rcu_head *rhp);
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#else
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#define do_trace_rcu_torture_read(rcutorturename, rhp) do { } while (0)
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#endif
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#endif
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#define UINT_CMP_GE(a, b) (UINT_MAX / 2 >= (a) - (b))
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#define UINT_CMP_LT(a, b) (UINT_MAX / 2 < (a) - (b))
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#define ULONG_CMP_GE(a, b) (ULONG_MAX / 2 >= (a) - (b))
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#define ULONG_CMP_LT(a, b) (ULONG_MAX / 2 < (a) - (b))
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/* Exported common interfaces */
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#ifdef CONFIG_PREEMPT_RCU
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/**
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* call_rcu() - Queue an RCU callback for invocation after a grace period.
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* @head: structure to be used for queueing the RCU updates.
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* @func: actual callback function to be invoked after the grace period
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*
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* The callback function will be invoked some time after a full grace
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* period elapses, in other words after all pre-existing RCU read-side
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* critical sections have completed. However, the callback function
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* might well execute concurrently with RCU read-side critical sections
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* that started after call_rcu() was invoked. 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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* Note that all CPUs must agree that the grace period extended beyond
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* all pre-existing RCU read-side critical section. On systems with more
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* than one CPU, this means that when "func()" is invoked, each CPU is
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* guaranteed to have executed a full memory barrier since the end of its
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* last RCU read-side critical section whose beginning preceded the call
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* to call_rcu(). It also means that each CPU executing an RCU read-side
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* critical section that continues beyond the start of "func()" must have
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* executed a memory barrier after the call_rcu() but before the beginning
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* of that RCU read-side critical section. Note that these guarantees
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* include CPUs that are offline, idle, or executing in user mode, as
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* well as CPUs that are executing in the kernel.
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*
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* Furthermore, if CPU A invoked call_rcu() and CPU B invoked the
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* resulting RCU callback function "func()", then both CPU A and CPU B are
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* guaranteed to execute a full memory barrier during the time interval
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* between the call to call_rcu() and the invocation of "func()" -- even
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* if CPU A and CPU B are the same CPU (but again only if the system has
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* more than one CPU).
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*/
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extern void call_rcu(struct rcu_head *head,
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void (*func)(struct rcu_head *head));
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#else /* #ifdef CONFIG_PREEMPT_RCU */
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/* In classic RCU, call_rcu() is just call_rcu_sched(). */
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#define call_rcu call_rcu_sched
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#endif /* #else #ifdef CONFIG_PREEMPT_RCU */
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/**
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* call_rcu_bh() - Queue an RCU for invocation after a quicker grace period.
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* @head: structure to be used for queueing the RCU updates.
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* @func: actual callback function to be invoked after the grace period
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*
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* The callback function will be invoked some time after a full grace
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* period elapses, in other words after all currently executing RCU
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* read-side critical sections have completed. call_rcu_bh() assumes
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* that the read-side critical sections end on completion of a softirq
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* handler. This means that read-side critical sections in process
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* context must not be interrupted by softirqs. This interface is to be
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* used when most of the read-side critical sections are in softirq context.
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* RCU read-side critical sections are delimited by :
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* - rcu_read_lock() and rcu_read_unlock(), if in interrupt context.
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* OR
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* - rcu_read_lock_bh() and rcu_read_unlock_bh(), if in process context.
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* These may be nested.
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*
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* See the description of call_rcu() for more detailed information on
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* memory ordering guarantees.
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*/
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extern void call_rcu_bh(struct rcu_head *head,
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void (*func)(struct rcu_head *head));
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/**
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* call_rcu_sched() - Queue an RCU for invocation after sched grace period.
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* @head: structure to be used for queueing the RCU updates.
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* @func: actual callback function to be invoked after the grace period
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*
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* The callback function will be invoked some time after a full grace
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* period elapses, in other words after all currently executing RCU
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* read-side critical sections have completed. call_rcu_sched() assumes
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* that the read-side critical sections end on enabling of preemption
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* or on voluntary preemption.
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* RCU read-side critical sections are delimited by :
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* - rcu_read_lock_sched() and rcu_read_unlock_sched(),
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* OR
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* anything that disables preemption.
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* These may be nested.
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*
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* See the description of call_rcu() for more detailed information on
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* memory ordering guarantees.
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*/
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extern void call_rcu_sched(struct rcu_head *head,
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void (*func)(struct rcu_head *rcu));
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extern void synchronize_sched(void);
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#ifdef CONFIG_PREEMPT_RCU
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extern void __rcu_read_lock(void);
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extern void __rcu_read_unlock(void);
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extern void rcu_read_unlock_special(struct task_struct *t);
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void synchronize_rcu(void);
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/*
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* Defined as a macro as it is a very low level header included from
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* areas that don't even know about current. This gives the rcu_read_lock()
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* nesting depth, but makes sense only if CONFIG_PREEMPT_RCU -- in other
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* types of kernel builds, the rcu_read_lock() nesting depth is unknowable.
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*/
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#define rcu_preempt_depth() (current->rcu_read_lock_nesting)
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#else /* #ifdef CONFIG_PREEMPT_RCU */
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static inline void __rcu_read_lock(void)
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{
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preempt_disable();
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}
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static inline void __rcu_read_unlock(void)
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{
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preempt_enable();
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}
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static inline void synchronize_rcu(void)
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{
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synchronize_sched();
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}
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static inline int rcu_preempt_depth(void)
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{
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return 0;
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}
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#endif /* #else #ifdef CONFIG_PREEMPT_RCU */
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/* Internal to kernel */
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extern void rcu_sched_qs(int cpu);
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extern void rcu_bh_qs(int cpu);
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extern void rcu_check_callbacks(int cpu, int user);
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struct notifier_block;
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extern void rcu_idle_enter(void);
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extern void rcu_idle_exit(void);
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extern void rcu_irq_enter(void);
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extern void rcu_irq_exit(void);
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#ifdef CONFIG_RCU_USER_QS
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extern void rcu_user_enter(void);
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extern void rcu_user_exit(void);
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extern void rcu_user_enter_after_irq(void);
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extern void rcu_user_exit_after_irq(void);
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#else
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static inline void rcu_user_enter(void) { }
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static inline void rcu_user_exit(void) { }
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static inline void rcu_user_enter_after_irq(void) { }
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static inline void rcu_user_exit_after_irq(void) { }
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static inline void rcu_user_hooks_switch(struct task_struct *prev,
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struct task_struct *next) { }
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#endif /* CONFIG_RCU_USER_QS */
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extern void exit_rcu(void);
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/**
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* RCU_NONIDLE - Indicate idle-loop code that needs RCU readers
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* @a: Code that RCU needs to pay attention to.
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*
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* RCU, RCU-bh, and RCU-sched read-side critical sections are forbidden
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* in the inner idle loop, that is, between the rcu_idle_enter() and
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* the rcu_idle_exit() -- RCU will happily ignore any such read-side
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* critical sections. However, things like powertop need tracepoints
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* in the inner idle loop.
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*
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* This macro provides the way out: RCU_NONIDLE(do_something_with_RCU())
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* will tell RCU that it needs to pay attending, invoke its argument
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* (in this example, a call to the do_something_with_RCU() function),
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* and then tell RCU to go back to ignoring this CPU. It is permissible
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* to nest RCU_NONIDLE() wrappers, but the nesting level is currently
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* quite limited. If deeper nesting is required, it will be necessary
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* to adjust DYNTICK_TASK_NESTING_VALUE accordingly.
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*/
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#define RCU_NONIDLE(a) \
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do { \
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rcu_irq_enter(); \
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do { a; } while (0); \
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rcu_irq_exit(); \
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} while (0)
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/*
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* Infrastructure to implement the synchronize_() primitives in
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* TREE_RCU and rcu_barrier_() primitives in TINY_RCU.
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*/
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typedef void call_rcu_func_t(struct rcu_head *head,
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void (*func)(struct rcu_head *head));
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void wait_rcu_gp(call_rcu_func_t crf);
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#if defined(CONFIG_TREE_RCU) || defined(CONFIG_TREE_PREEMPT_RCU)
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#include <linux/rcutree.h>
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#elif defined(CONFIG_TINY_RCU) || defined(CONFIG_TINY_PREEMPT_RCU)
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#include <linux/rcutiny.h>
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#else
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#error "Unknown RCU implementation specified to kernel configuration"
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#endif
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/*
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* init_rcu_head_on_stack()/destroy_rcu_head_on_stack() are needed for dynamic
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* initialization and destruction of rcu_head on the stack. rcu_head structures
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* allocated dynamically in the heap or defined statically don't need any
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* initialization.
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*/
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#ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD
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extern void init_rcu_head_on_stack(struct rcu_head *head);
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extern void destroy_rcu_head_on_stack(struct rcu_head *head);
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#else /* !CONFIG_DEBUG_OBJECTS_RCU_HEAD */
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static inline void init_rcu_head_on_stack(struct rcu_head *head)
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{
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}
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static inline void destroy_rcu_head_on_stack(struct rcu_head *head)
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{
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}
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#endif /* #else !CONFIG_DEBUG_OBJECTS_RCU_HEAD */
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#if defined(CONFIG_DEBUG_LOCK_ALLOC) || defined(CONFIG_SMP)
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extern int rcu_is_cpu_idle(void);
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#endif /* #if defined(CONFIG_DEBUG_LOCK_ALLOC) || defined(CONFIG_SMP) */
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#if defined(CONFIG_HOTPLUG_CPU) && defined(CONFIG_PROVE_RCU)
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bool rcu_lockdep_current_cpu_online(void);
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#else /* #if defined(CONFIG_HOTPLUG_CPU) && defined(CONFIG_PROVE_RCU) */
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static inline bool rcu_lockdep_current_cpu_online(void)
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{
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return 1;
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}
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#endif /* #else #if defined(CONFIG_HOTPLUG_CPU) && defined(CONFIG_PROVE_RCU) */
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#ifdef CONFIG_DEBUG_LOCK_ALLOC
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static inline void rcu_lock_acquire(struct lockdep_map *map)
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{
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lock_acquire(map, 0, 0, 2, 1, NULL, _THIS_IP_);
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}
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static inline void rcu_lock_release(struct lockdep_map *map)
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{
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lock_release(map, 1, _THIS_IP_);
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}
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extern struct lockdep_map rcu_lock_map;
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extern struct lockdep_map rcu_bh_lock_map;
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extern struct lockdep_map rcu_sched_lock_map;
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extern int debug_lockdep_rcu_enabled(void);
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/**
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* rcu_read_lock_held() - might we be in RCU read-side critical section?
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*
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* If CONFIG_DEBUG_LOCK_ALLOC is selected, returns nonzero iff in an RCU
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* read-side critical section. In absence of CONFIG_DEBUG_LOCK_ALLOC,
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* this assumes we are in an RCU read-side critical section unless it can
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* prove otherwise. This is useful for debug checks in functions that
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* require that they be called within an RCU read-side critical section.
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*
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* Checks debug_lockdep_rcu_enabled() to prevent false positives during boot
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* and while lockdep is disabled.
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*
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* Note that rcu_read_lock() and the matching rcu_read_unlock() must
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* occur in the same context, for example, it is illegal to invoke
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* rcu_read_unlock() in process context if the matching rcu_read_lock()
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* was invoked from within an irq handler.
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*
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* Note that rcu_read_lock() is disallowed if the CPU is either idle or
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* offline from an RCU perspective, so check for those as well.
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*/
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static inline int rcu_read_lock_held(void)
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{
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if (!debug_lockdep_rcu_enabled())
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return 1;
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if (rcu_is_cpu_idle())
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return 0;
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if (!rcu_lockdep_current_cpu_online())
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return 0;
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return lock_is_held(&rcu_lock_map);
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}
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/*
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* rcu_read_lock_bh_held() is defined out of line to avoid #include-file
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* hell.
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*/
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extern int rcu_read_lock_bh_held(void);
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/**
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* rcu_read_lock_sched_held() - might we be in RCU-sched read-side critical section?
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*
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* If CONFIG_DEBUG_LOCK_ALLOC is selected, returns nonzero iff in an
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* RCU-sched read-side critical section. In absence of
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* CONFIG_DEBUG_LOCK_ALLOC, this assumes we are in an RCU-sched read-side
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* critical section unless it can prove otherwise. Note that disabling
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* of preemption (including disabling irqs) counts as an RCU-sched
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* read-side critical section. This is useful for debug checks in functions
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* that required that they be called within an RCU-sched read-side
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* critical section.
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*
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* Check debug_lockdep_rcu_enabled() to prevent false positives during boot
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* and while lockdep is disabled.
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*
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* Note that if the CPU is in the idle loop from an RCU point of
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* view (ie: that we are in the section between rcu_idle_enter() and
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* rcu_idle_exit()) then rcu_read_lock_held() returns false even if the CPU
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* did an rcu_read_lock(). The reason for this is that RCU ignores CPUs
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* that are in such a section, considering these as in extended quiescent
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* state, so such a CPU is effectively never in an RCU read-side critical
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* section regardless of what RCU primitives it invokes. This state of
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* affairs is required --- we need to keep an RCU-free window in idle
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* where the CPU may possibly enter into low power mode. This way we can
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* notice an extended quiescent state to other CPUs that started a grace
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* period. Otherwise we would delay any grace period as long as we run in
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* the idle task.
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*
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* Similarly, we avoid claiming an SRCU read lock held if the current
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* CPU is offline.
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*/
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#ifdef CONFIG_PREEMPT_COUNT
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static inline int rcu_read_lock_sched_held(void)
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{
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int lockdep_opinion = 0;
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if (!debug_lockdep_rcu_enabled())
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return 1;
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if (rcu_is_cpu_idle())
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return 0;
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if (!rcu_lockdep_current_cpu_online())
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return 0;
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if (debug_locks)
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lockdep_opinion = lock_is_held(&rcu_sched_lock_map);
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return lockdep_opinion || preempt_count() != 0 || irqs_disabled();
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}
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#else /* #ifdef CONFIG_PREEMPT_COUNT */
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static inline int rcu_read_lock_sched_held(void)
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{
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return 1;
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}
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#endif /* #else #ifdef CONFIG_PREEMPT_COUNT */
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#else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
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# define rcu_lock_acquire(a) do { } while (0)
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# define rcu_lock_release(a) do { } while (0)
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static inline int rcu_read_lock_held(void)
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{
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return 1;
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}
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static inline int rcu_read_lock_bh_held(void)
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{
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return 1;
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}
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#ifdef CONFIG_PREEMPT_COUNT
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static inline int rcu_read_lock_sched_held(void)
|
|
{
|
|
return preempt_count() != 0 || irqs_disabled();
|
|
}
|
|
#else /* #ifdef CONFIG_PREEMPT_COUNT */
|
|
static inline int rcu_read_lock_sched_held(void)
|
|
{
|
|
return 1;
|
|
}
|
|
#endif /* #else #ifdef CONFIG_PREEMPT_COUNT */
|
|
|
|
#endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */
|
|
|
|
#ifdef CONFIG_PROVE_RCU
|
|
|
|
extern int rcu_my_thread_group_empty(void);
|
|
|
|
/**
|
|
* rcu_lockdep_assert - emit lockdep splat if specified condition not met
|
|
* @c: condition to check
|
|
* @s: informative message
|
|
*/
|
|
#define rcu_lockdep_assert(c, s) \
|
|
do { \
|
|
static bool __section(.data.unlikely) __warned; \
|
|
if (debug_lockdep_rcu_enabled() && !__warned && !(c)) { \
|
|
__warned = true; \
|
|
lockdep_rcu_suspicious(__FILE__, __LINE__, s); \
|
|
} \
|
|
} while (0)
|
|
|
|
#if defined(CONFIG_PROVE_RCU) && !defined(CONFIG_PREEMPT_RCU)
|
|
static inline void rcu_preempt_sleep_check(void)
|
|
{
|
|
rcu_lockdep_assert(!lock_is_held(&rcu_lock_map),
|
|
"Illegal context switch in RCU read-side critical section");
|
|
}
|
|
#else /* #ifdef CONFIG_PROVE_RCU */
|
|
static inline void rcu_preempt_sleep_check(void)
|
|
{
|
|
}
|
|
#endif /* #else #ifdef CONFIG_PROVE_RCU */
|
|
|
|
#define rcu_sleep_check() \
|
|
do { \
|
|
rcu_preempt_sleep_check(); \
|
|
rcu_lockdep_assert(!lock_is_held(&rcu_bh_lock_map), \
|
|
"Illegal context switch in RCU-bh" \
|
|
" read-side critical section"); \
|
|
rcu_lockdep_assert(!lock_is_held(&rcu_sched_lock_map), \
|
|
"Illegal context switch in RCU-sched"\
|
|
" read-side critical section"); \
|
|
} while (0)
|
|
|
|
#else /* #ifdef CONFIG_PROVE_RCU */
|
|
|
|
#define rcu_lockdep_assert(c, s) do { } while (0)
|
|
#define rcu_sleep_check() do { } while (0)
|
|
|
|
#endif /* #else #ifdef CONFIG_PROVE_RCU */
|
|
|
|
/*
|
|
* Helper functions for rcu_dereference_check(), rcu_dereference_protected()
|
|
* and rcu_assign_pointer(). Some of these could be folded into their
|
|
* callers, but they are left separate in order to ease introduction of
|
|
* multiple flavors of pointers to match the multiple flavors of RCU
|
|
* (e.g., __rcu_bh, * __rcu_sched, and __srcu), should this make sense in
|
|
* the future.
|
|
*/
|
|
|
|
#ifdef __CHECKER__
|
|
#define rcu_dereference_sparse(p, space) \
|
|
((void)(((typeof(*p) space *)p) == p))
|
|
#else /* #ifdef __CHECKER__ */
|
|
#define rcu_dereference_sparse(p, space)
|
|
#endif /* #else #ifdef __CHECKER__ */
|
|
|
|
#define __rcu_access_pointer(p, space) \
|
|
({ \
|
|
typeof(*p) *_________p1 = (typeof(*p)*__force )ACCESS_ONCE(p); \
|
|
rcu_dereference_sparse(p, space); \
|
|
((typeof(*p) __force __kernel *)(_________p1)); \
|
|
})
|
|
#define __rcu_dereference_check(p, c, space) \
|
|
({ \
|
|
typeof(*p) *_________p1 = (typeof(*p)*__force )ACCESS_ONCE(p); \
|
|
rcu_lockdep_assert(c, "suspicious rcu_dereference_check()" \
|
|
" usage"); \
|
|
rcu_dereference_sparse(p, space); \
|
|
smp_read_barrier_depends(); \
|
|
((typeof(*p) __force __kernel *)(_________p1)); \
|
|
})
|
|
#define __rcu_dereference_protected(p, c, space) \
|
|
({ \
|
|
rcu_lockdep_assert(c, "suspicious rcu_dereference_protected()" \
|
|
" usage"); \
|
|
rcu_dereference_sparse(p, space); \
|
|
((typeof(*p) __force __kernel *)(p)); \
|
|
})
|
|
|
|
#define __rcu_access_index(p, space) \
|
|
({ \
|
|
typeof(p) _________p1 = ACCESS_ONCE(p); \
|
|
rcu_dereference_sparse(p, space); \
|
|
(_________p1); \
|
|
})
|
|
#define __rcu_dereference_index_check(p, c) \
|
|
({ \
|
|
typeof(p) _________p1 = ACCESS_ONCE(p); \
|
|
rcu_lockdep_assert(c, \
|
|
"suspicious rcu_dereference_index_check()" \
|
|
" usage"); \
|
|
smp_read_barrier_depends(); \
|
|
(_________p1); \
|
|
})
|
|
#define __rcu_assign_pointer(p, v, space) \
|
|
do { \
|
|
smp_wmb(); \
|
|
(p) = (typeof(*v) __force space *)(v); \
|
|
} while (0)
|
|
|
|
|
|
/**
|
|
* rcu_access_pointer() - fetch RCU pointer with no dereferencing
|
|
* @p: The pointer to read
|
|
*
|
|
* Return the value of the specified RCU-protected pointer, but omit the
|
|
* smp_read_barrier_depends() and keep the ACCESS_ONCE(). This is useful
|
|
* when the value of this pointer is accessed, but the pointer is not
|
|
* dereferenced, for example, when testing an RCU-protected pointer against
|
|
* NULL. Although rcu_access_pointer() may also be used in cases where
|
|
* update-side locks prevent the value of the pointer from changing, you
|
|
* should instead use rcu_dereference_protected() for this use case.
|
|
*
|
|
* It is also permissible to use rcu_access_pointer() when read-side
|
|
* access to the pointer was removed at least one grace period ago, as
|
|
* is the case in the context of the RCU callback that is freeing up
|
|
* the data, or after a synchronize_rcu() returns. This can be useful
|
|
* when tearing down multi-linked structures after a grace period
|
|
* has elapsed.
|
|
*/
|
|
#define rcu_access_pointer(p) __rcu_access_pointer((p), __rcu)
|
|
|
|
/**
|
|
* rcu_dereference_check() - rcu_dereference with debug checking
|
|
* @p: The pointer to read, prior to dereferencing
|
|
* @c: The conditions under which the dereference will take place
|
|
*
|
|
* Do an rcu_dereference(), but check that the conditions under which the
|
|
* dereference will take place are correct. Typically the conditions
|
|
* indicate the various locking conditions that should be held at that
|
|
* point. The check should return true if the conditions are satisfied.
|
|
* An implicit check for being in an RCU read-side critical section
|
|
* (rcu_read_lock()) is included.
|
|
*
|
|
* For example:
|
|
*
|
|
* bar = rcu_dereference_check(foo->bar, lockdep_is_held(&foo->lock));
|
|
*
|
|
* could be used to indicate to lockdep that foo->bar may only be dereferenced
|
|
* if either rcu_read_lock() is held, or that the lock required to replace
|
|
* the bar struct at foo->bar is held.
|
|
*
|
|
* Note that the list of conditions may also include indications of when a lock
|
|
* need not be held, for example during initialisation or destruction of the
|
|
* target struct:
|
|
*
|
|
* bar = rcu_dereference_check(foo->bar, lockdep_is_held(&foo->lock) ||
|
|
* atomic_read(&foo->usage) == 0);
|
|
*
|
|
* Inserts memory barriers on architectures that require them
|
|
* (currently only the Alpha), prevents the compiler from refetching
|
|
* (and from merging fetches), and, more importantly, documents exactly
|
|
* which pointers are protected by RCU and checks that the pointer is
|
|
* annotated as __rcu.
|
|
*/
|
|
#define rcu_dereference_check(p, c) \
|
|
__rcu_dereference_check((p), rcu_read_lock_held() || (c), __rcu)
|
|
|
|
/**
|
|
* rcu_dereference_bh_check() - rcu_dereference_bh with debug checking
|
|
* @p: The pointer to read, prior to dereferencing
|
|
* @c: The conditions under which the dereference will take place
|
|
*
|
|
* This is the RCU-bh counterpart to rcu_dereference_check().
|
|
*/
|
|
#define rcu_dereference_bh_check(p, c) \
|
|
__rcu_dereference_check((p), rcu_read_lock_bh_held() || (c), __rcu)
|
|
|
|
/**
|
|
* rcu_dereference_sched_check() - rcu_dereference_sched with debug checking
|
|
* @p: The pointer to read, prior to dereferencing
|
|
* @c: The conditions under which the dereference will take place
|
|
*
|
|
* This is the RCU-sched counterpart to rcu_dereference_check().
|
|
*/
|
|
#define rcu_dereference_sched_check(p, c) \
|
|
__rcu_dereference_check((p), rcu_read_lock_sched_held() || (c), \
|
|
__rcu)
|
|
|
|
#define rcu_dereference_raw(p) rcu_dereference_check(p, 1) /*@@@ needed? @@@*/
|
|
|
|
/**
|
|
* rcu_access_index() - fetch RCU index with no dereferencing
|
|
* @p: The index to read
|
|
*
|
|
* Return the value of the specified RCU-protected index, but omit the
|
|
* smp_read_barrier_depends() and keep the ACCESS_ONCE(). This is useful
|
|
* when the value of this index is accessed, but the index is not
|
|
* dereferenced, for example, when testing an RCU-protected index against
|
|
* -1. Although rcu_access_index() may also be used in cases where
|
|
* update-side locks prevent the value of the index from changing, you
|
|
* should instead use rcu_dereference_index_protected() for this use case.
|
|
*/
|
|
#define rcu_access_index(p) __rcu_access_index((p), __rcu)
|
|
|
|
/**
|
|
* rcu_dereference_index_check() - rcu_dereference for indices with debug checking
|
|
* @p: The pointer to read, prior to dereferencing
|
|
* @c: The conditions under which the dereference will take place
|
|
*
|
|
* Similar to rcu_dereference_check(), but omits the sparse checking.
|
|
* This allows rcu_dereference_index_check() to be used on integers,
|
|
* which can then be used as array indices. Attempting to use
|
|
* rcu_dereference_check() on an integer will give compiler warnings
|
|
* because the sparse address-space mechanism relies on dereferencing
|
|
* the RCU-protected pointer. Dereferencing integers is not something
|
|
* that even gcc will put up with.
|
|
*
|
|
* Note that this function does not implicitly check for RCU read-side
|
|
* critical sections. If this function gains lots of uses, it might
|
|
* make sense to provide versions for each flavor of RCU, but it does
|
|
* not make sense as of early 2010.
|
|
*/
|
|
#define rcu_dereference_index_check(p, c) \
|
|
__rcu_dereference_index_check((p), (c))
|
|
|
|
/**
|
|
* rcu_dereference_protected() - fetch RCU pointer when updates prevented
|
|
* @p: The pointer to read, prior to dereferencing
|
|
* @c: The conditions under which the dereference will take place
|
|
*
|
|
* Return the value of the specified RCU-protected pointer, but omit
|
|
* both the smp_read_barrier_depends() and the ACCESS_ONCE(). This
|
|
* is useful in cases where update-side locks prevent the value of the
|
|
* pointer from changing. Please note that this primitive does -not-
|
|
* prevent the compiler from repeating this reference or combining it
|
|
* with other references, so it should not be used without protection
|
|
* of appropriate locks.
|
|
*
|
|
* This function is only for update-side use. Using this function
|
|
* when protected only by rcu_read_lock() will result in infrequent
|
|
* but very ugly failures.
|
|
*/
|
|
#define rcu_dereference_protected(p, c) \
|
|
__rcu_dereference_protected((p), (c), __rcu)
|
|
|
|
|
|
/**
|
|
* rcu_dereference() - fetch RCU-protected pointer for dereferencing
|
|
* @p: The pointer to read, prior to dereferencing
|
|
*
|
|
* This is a simple wrapper around rcu_dereference_check().
|
|
*/
|
|
#define rcu_dereference(p) rcu_dereference_check(p, 0)
|
|
|
|
/**
|
|
* rcu_dereference_bh() - fetch an RCU-bh-protected pointer for dereferencing
|
|
* @p: The pointer to read, prior to dereferencing
|
|
*
|
|
* Makes rcu_dereference_check() do the dirty work.
|
|
*/
|
|
#define rcu_dereference_bh(p) rcu_dereference_bh_check(p, 0)
|
|
|
|
/**
|
|
* rcu_dereference_sched() - fetch RCU-sched-protected pointer for dereferencing
|
|
* @p: The pointer to read, prior to dereferencing
|
|
*
|
|
* Makes rcu_dereference_check() do the dirty work.
|
|
*/
|
|
#define rcu_dereference_sched(p) rcu_dereference_sched_check(p, 0)
|
|
|
|
/**
|
|
* rcu_read_lock() - mark the beginning of an RCU read-side critical section
|
|
*
|
|
* When synchronize_rcu() is invoked on one CPU while other CPUs
|
|
* are within RCU read-side critical sections, then the
|
|
* synchronize_rcu() is guaranteed to block until after all the other
|
|
* CPUs exit their critical sections. Similarly, if call_rcu() is invoked
|
|
* on one CPU while other CPUs are within RCU read-side critical
|
|
* sections, invocation of the corresponding RCU callback is deferred
|
|
* until after the all the other CPUs exit their critical sections.
|
|
*
|
|
* Note, however, that RCU callbacks are permitted to run concurrently
|
|
* with new RCU read-side critical sections. One way that this can happen
|
|
* is via the following sequence of events: (1) CPU 0 enters an RCU
|
|
* read-side critical section, (2) CPU 1 invokes call_rcu() to register
|
|
* an RCU callback, (3) CPU 0 exits the RCU read-side critical section,
|
|
* (4) CPU 2 enters a RCU read-side critical section, (5) the RCU
|
|
* callback is invoked. This is legal, because the RCU read-side critical
|
|
* section that was running concurrently with the call_rcu() (and which
|
|
* therefore might be referencing something that the corresponding RCU
|
|
* callback would free up) has completed before the corresponding
|
|
* RCU callback is invoked.
|
|
*
|
|
* RCU read-side critical sections may be nested. Any deferred actions
|
|
* will be deferred until the outermost RCU read-side critical section
|
|
* completes.
|
|
*
|
|
* You can avoid reading and understanding the next paragraph by
|
|
* following this rule: don't put anything in an rcu_read_lock() RCU
|
|
* read-side critical section that would block in a !PREEMPT kernel.
|
|
* But if you want the full story, read on!
|
|
*
|
|
* In non-preemptible RCU implementations (TREE_RCU and TINY_RCU), it
|
|
* is illegal to block while in an RCU read-side critical section. In
|
|
* preemptible RCU implementations (TREE_PREEMPT_RCU and TINY_PREEMPT_RCU)
|
|
* in CONFIG_PREEMPT kernel builds, RCU read-side critical sections may
|
|
* be preempted, but explicit blocking is illegal. Finally, in preemptible
|
|
* RCU implementations in real-time (CONFIG_PREEMPT_RT) kernel builds,
|
|
* RCU read-side critical sections may be preempted and they may also
|
|
* block, but only when acquiring spinlocks that are subject to priority
|
|
* inheritance.
|
|
*/
|
|
static inline void rcu_read_lock(void)
|
|
{
|
|
__rcu_read_lock();
|
|
__acquire(RCU);
|
|
rcu_lock_acquire(&rcu_lock_map);
|
|
rcu_lockdep_assert(!rcu_is_cpu_idle(),
|
|
"rcu_read_lock() used illegally while idle");
|
|
}
|
|
|
|
/*
|
|
* So where is rcu_write_lock()? It does not exist, as there is no
|
|
* way for writers to lock out RCU readers. This is a feature, not
|
|
* a bug -- this property is what provides RCU's performance benefits.
|
|
* Of course, writers must coordinate with each other. The normal
|
|
* spinlock primitives work well for this, but any other technique may be
|
|
* used as well. RCU does not care how the writers keep out of each
|
|
* others' way, as long as they do so.
|
|
*/
|
|
|
|
/**
|
|
* rcu_read_unlock() - marks the end of an RCU read-side critical section.
|
|
*
|
|
* See rcu_read_lock() for more information.
|
|
*/
|
|
static inline void rcu_read_unlock(void)
|
|
{
|
|
rcu_lockdep_assert(!rcu_is_cpu_idle(),
|
|
"rcu_read_unlock() used illegally while idle");
|
|
rcu_lock_release(&rcu_lock_map);
|
|
__release(RCU);
|
|
__rcu_read_unlock();
|
|
}
|
|
|
|
/**
|
|
* rcu_read_lock_bh() - mark the beginning of an RCU-bh critical section
|
|
*
|
|
* This is equivalent of rcu_read_lock(), but to be used when updates
|
|
* are being done using call_rcu_bh() or synchronize_rcu_bh(). Since
|
|
* both call_rcu_bh() and synchronize_rcu_bh() consider completion of a
|
|
* softirq handler to be a quiescent state, a process in RCU read-side
|
|
* critical section must be protected by disabling softirqs. Read-side
|
|
* critical sections in interrupt context can use just rcu_read_lock(),
|
|
* though this should at least be commented to avoid confusing people
|
|
* reading the code.
|
|
*
|
|
* Note that rcu_read_lock_bh() and the matching rcu_read_unlock_bh()
|
|
* must occur in the same context, for example, it is illegal to invoke
|
|
* rcu_read_unlock_bh() from one task if the matching rcu_read_lock_bh()
|
|
* was invoked from some other task.
|
|
*/
|
|
static inline void rcu_read_lock_bh(void)
|
|
{
|
|
local_bh_disable();
|
|
__acquire(RCU_BH);
|
|
rcu_lock_acquire(&rcu_bh_lock_map);
|
|
rcu_lockdep_assert(!rcu_is_cpu_idle(),
|
|
"rcu_read_lock_bh() used illegally while idle");
|
|
}
|
|
|
|
/*
|
|
* rcu_read_unlock_bh - marks the end of a softirq-only RCU critical section
|
|
*
|
|
* See rcu_read_lock_bh() for more information.
|
|
*/
|
|
static inline void rcu_read_unlock_bh(void)
|
|
{
|
|
rcu_lockdep_assert(!rcu_is_cpu_idle(),
|
|
"rcu_read_unlock_bh() used illegally while idle");
|
|
rcu_lock_release(&rcu_bh_lock_map);
|
|
__release(RCU_BH);
|
|
local_bh_enable();
|
|
}
|
|
|
|
/**
|
|
* rcu_read_lock_sched() - mark the beginning of a RCU-sched critical section
|
|
*
|
|
* This is equivalent of rcu_read_lock(), but to be used when updates
|
|
* are being done using call_rcu_sched() or synchronize_rcu_sched().
|
|
* Read-side critical sections can also be introduced by anything that
|
|
* disables preemption, including local_irq_disable() and friends.
|
|
*
|
|
* Note that rcu_read_lock_sched() and the matching rcu_read_unlock_sched()
|
|
* must occur in the same context, for example, it is illegal to invoke
|
|
* rcu_read_unlock_sched() from process context if the matching
|
|
* rcu_read_lock_sched() was invoked from an NMI handler.
|
|
*/
|
|
static inline void rcu_read_lock_sched(void)
|
|
{
|
|
preempt_disable();
|
|
__acquire(RCU_SCHED);
|
|
rcu_lock_acquire(&rcu_sched_lock_map);
|
|
rcu_lockdep_assert(!rcu_is_cpu_idle(),
|
|
"rcu_read_lock_sched() used illegally while idle");
|
|
}
|
|
|
|
/* Used by lockdep and tracing: cannot be traced, cannot call lockdep. */
|
|
static inline notrace void rcu_read_lock_sched_notrace(void)
|
|
{
|
|
preempt_disable_notrace();
|
|
__acquire(RCU_SCHED);
|
|
}
|
|
|
|
/*
|
|
* rcu_read_unlock_sched - marks the end of a RCU-classic critical section
|
|
*
|
|
* See rcu_read_lock_sched for more information.
|
|
*/
|
|
static inline void rcu_read_unlock_sched(void)
|
|
{
|
|
rcu_lockdep_assert(!rcu_is_cpu_idle(),
|
|
"rcu_read_unlock_sched() used illegally while idle");
|
|
rcu_lock_release(&rcu_sched_lock_map);
|
|
__release(RCU_SCHED);
|
|
preempt_enable();
|
|
}
|
|
|
|
/* Used by lockdep and tracing: cannot be traced, cannot call lockdep. */
|
|
static inline notrace void rcu_read_unlock_sched_notrace(void)
|
|
{
|
|
__release(RCU_SCHED);
|
|
preempt_enable_notrace();
|
|
}
|
|
|
|
/**
|
|
* rcu_assign_pointer() - assign to RCU-protected pointer
|
|
* @p: pointer to assign to
|
|
* @v: value to assign (publish)
|
|
*
|
|
* Assigns the specified value to the specified RCU-protected
|
|
* pointer, ensuring that any concurrent RCU readers will see
|
|
* any prior initialization.
|
|
*
|
|
* Inserts memory barriers on architectures that require them
|
|
* (which is most of them), and also prevents the compiler from
|
|
* reordering the code that initializes the structure after the pointer
|
|
* assignment. More importantly, this call documents which pointers
|
|
* will be dereferenced by RCU read-side code.
|
|
*
|
|
* In some special cases, you may use RCU_INIT_POINTER() instead
|
|
* of rcu_assign_pointer(). RCU_INIT_POINTER() is a bit faster due
|
|
* to the fact that it does not constrain either the CPU or the compiler.
|
|
* That said, using RCU_INIT_POINTER() when you should have used
|
|
* rcu_assign_pointer() is a very bad thing that results in
|
|
* impossible-to-diagnose memory corruption. So please be careful.
|
|
* See the RCU_INIT_POINTER() comment header for details.
|
|
*/
|
|
#define rcu_assign_pointer(p, v) \
|
|
__rcu_assign_pointer((p), (v), __rcu)
|
|
|
|
/**
|
|
* RCU_INIT_POINTER() - initialize an RCU protected pointer
|
|
*
|
|
* Initialize an RCU-protected pointer in special cases where readers
|
|
* do not need ordering constraints on the CPU or the compiler. These
|
|
* special cases are:
|
|
*
|
|
* 1. This use of RCU_INIT_POINTER() is NULLing out the pointer -or-
|
|
* 2. The caller has taken whatever steps are required to prevent
|
|
* RCU readers from concurrently accessing this pointer -or-
|
|
* 3. The referenced data structure has already been exposed to
|
|
* readers either at compile time or via rcu_assign_pointer() -and-
|
|
* a. You have not made -any- reader-visible changes to
|
|
* this structure since then -or-
|
|
* b. It is OK for readers accessing this structure from its
|
|
* new location to see the old state of the structure. (For
|
|
* example, the changes were to statistical counters or to
|
|
* other state where exact synchronization is not required.)
|
|
*
|
|
* Failure to follow these rules governing use of RCU_INIT_POINTER() will
|
|
* result in impossible-to-diagnose memory corruption. As in the structures
|
|
* will look OK in crash dumps, but any concurrent RCU readers might
|
|
* see pre-initialized values of the referenced data structure. So
|
|
* please be very careful how you use RCU_INIT_POINTER()!!!
|
|
*
|
|
* If you are creating an RCU-protected linked structure that is accessed
|
|
* by a single external-to-structure RCU-protected pointer, then you may
|
|
* use RCU_INIT_POINTER() to initialize the internal RCU-protected
|
|
* pointers, but you must use rcu_assign_pointer() to initialize the
|
|
* external-to-structure pointer -after- you have completely initialized
|
|
* the reader-accessible portions of the linked structure.
|
|
*/
|
|
#define RCU_INIT_POINTER(p, v) \
|
|
do { \
|
|
p = (typeof(*v) __force __rcu *)(v); \
|
|
} while (0)
|
|
|
|
/**
|
|
* RCU_POINTER_INITIALIZER() - statically initialize an RCU protected pointer
|
|
*
|
|
* GCC-style initialization for an RCU-protected pointer in a structure field.
|
|
*/
|
|
#define RCU_POINTER_INITIALIZER(p, v) \
|
|
.p = (typeof(*v) __force __rcu *)(v)
|
|
|
|
/*
|
|
* Does the specified offset indicate that the corresponding rcu_head
|
|
* structure can be handled by kfree_rcu()?
|
|
*/
|
|
#define __is_kfree_rcu_offset(offset) ((offset) < 4096)
|
|
|
|
/*
|
|
* Helper macro for kfree_rcu() to prevent argument-expansion eyestrain.
|
|
*/
|
|
#define __kfree_rcu(head, offset) \
|
|
do { \
|
|
BUILD_BUG_ON(!__is_kfree_rcu_offset(offset)); \
|
|
kfree_call_rcu(head, (void (*)(struct rcu_head *))(unsigned long)(offset)); \
|
|
} while (0)
|
|
|
|
/**
|
|
* kfree_rcu() - kfree an object after a grace period.
|
|
* @ptr: pointer to kfree
|
|
* @rcu_head: the name of the struct rcu_head within the type of @ptr.
|
|
*
|
|
* Many rcu callbacks functions just call kfree() on the base structure.
|
|
* These functions are trivial, but their size adds up, and furthermore
|
|
* when they are used in a kernel module, that module must invoke the
|
|
* high-latency rcu_barrier() function at module-unload time.
|
|
*
|
|
* The kfree_rcu() function handles this issue. Rather than encoding a
|
|
* function address in the embedded rcu_head structure, kfree_rcu() instead
|
|
* encodes the offset of the rcu_head structure within the base structure.
|
|
* Because the functions are not allowed in the low-order 4096 bytes of
|
|
* kernel virtual memory, offsets up to 4095 bytes can be accommodated.
|
|
* If the offset is larger than 4095 bytes, a compile-time error will
|
|
* be generated in __kfree_rcu(). If this error is triggered, you can
|
|
* either fall back to use of call_rcu() or rearrange the structure to
|
|
* position the rcu_head structure into the first 4096 bytes.
|
|
*
|
|
* Note that the allowable offset might decrease in the future, for example,
|
|
* to allow something like kmem_cache_free_rcu().
|
|
*
|
|
* The BUILD_BUG_ON check must not involve any function calls, hence the
|
|
* checks are done in macros here.
|
|
*/
|
|
#define kfree_rcu(ptr, rcu_head) \
|
|
__kfree_rcu(&((ptr)->rcu_head), offsetof(typeof(*(ptr)), rcu_head))
|
|
|
|
#endif /* __LINUX_RCUPDATE_H */
|