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![Paul E. McKenney](/assets/img/avatar_default.png)
The intent is that a given RCU read-side critical section be confined to a single context. For example, it is illegal to invoke rcu_read_lock() in an exception handler and then invoke rcu_read_unlock() from the context of the task that received the exception. Suggested-by: Peter Zijlstra <peterz@infradead.org> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
873 lines
31 KiB
C
873 lines
31 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/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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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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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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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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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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/*
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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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#ifdef CONFIG_DEBUG_LOCK_ALLOC
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#ifdef CONFIG_PROVE_RCU
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extern int rcu_is_cpu_idle(void);
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#else /* !CONFIG_PROVE_RCU */
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static inline int rcu_is_cpu_idle(void)
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{
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return 0;
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}
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#endif /* else !CONFIG_PROVE_RCU */
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static inline void rcu_lock_acquire(struct lockdep_map *map)
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{
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WARN_ON_ONCE(rcu_is_cpu_idle());
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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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WARN_ON_ONCE(rcu_is_cpu_idle());
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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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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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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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#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 (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)
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{
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return 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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#endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */
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#ifdef CONFIG_PROVE_RCU
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extern int rcu_my_thread_group_empty(void);
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/**
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* rcu_lockdep_assert - emit lockdep splat if specified condition not met
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* @c: condition to check
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* @s: informative message
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*/
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#define rcu_lockdep_assert(c, s) \
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do { \
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static bool __warned; \
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if (debug_lockdep_rcu_enabled() && !__warned && !(c)) { \
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__warned = true; \
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lockdep_rcu_suspicious(__FILE__, __LINE__, s); \
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} \
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} while (0)
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#define rcu_sleep_check() \
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do { \
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rcu_lockdep_assert(!lock_is_held(&rcu_bh_lock_map), \
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"Illegal context switch in RCU-bh" \
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" read-side critical section"); \
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rcu_lockdep_assert(!lock_is_held(&rcu_sched_lock_map), \
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"Illegal context switch in RCU-sched"\
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" read-side critical section"); \
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} while (0)
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#else /* #ifdef CONFIG_PROVE_RCU */
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#define rcu_lockdep_assert(c, s) do { } while (0)
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#define rcu_sleep_check() do { } while (0)
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#endif /* #else #ifdef CONFIG_PROVE_RCU */
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/*
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* Helper functions for rcu_dereference_check(), rcu_dereference_protected()
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* and rcu_assign_pointer(). Some of these could be folded into their
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* callers, but they are left separate in order to ease introduction of
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* multiple flavors of pointers to match the multiple flavors of RCU
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* (e.g., __rcu_bh, * __rcu_sched, and __srcu), should this make sense in
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* the future.
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*/
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#ifdef __CHECKER__
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#define rcu_dereference_sparse(p, space) \
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((void)(((typeof(*p) space *)p) == p))
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#else /* #ifdef __CHECKER__ */
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#define rcu_dereference_sparse(p, space)
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#endif /* #else #ifdef __CHECKER__ */
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#define __rcu_access_pointer(p, space) \
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({ \
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typeof(*p) *_________p1 = (typeof(*p)*__force )ACCESS_ONCE(p); \
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rcu_dereference_sparse(p, space); \
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((typeof(*p) __force __kernel *)(_________p1)); \
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})
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#define __rcu_dereference_check(p, c, space) \
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({ \
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typeof(*p) *_________p1 = (typeof(*p)*__force )ACCESS_ONCE(p); \
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rcu_lockdep_assert(c, "suspicious rcu_dereference_check()" \
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" usage"); \
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rcu_dereference_sparse(p, space); \
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smp_read_barrier_depends(); \
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((typeof(*p) __force __kernel *)(_________p1)); \
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})
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#define __rcu_dereference_protected(p, c, space) \
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({ \
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rcu_lockdep_assert(c, "suspicious rcu_dereference_protected()" \
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" usage"); \
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rcu_dereference_sparse(p, space); \
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((typeof(*p) __force __kernel *)(p)); \
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})
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#define __rcu_access_index(p, space) \
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({ \
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typeof(p) _________p1 = ACCESS_ONCE(p); \
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rcu_dereference_sparse(p, space); \
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(_________p1); \
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})
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#define __rcu_dereference_index_check(p, c) \
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({ \
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typeof(p) _________p1 = ACCESS_ONCE(p); \
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rcu_lockdep_assert(c, \
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"suspicious rcu_dereference_index_check()" \
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" usage"); \
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smp_read_barrier_depends(); \
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(_________p1); \
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})
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#define __rcu_assign_pointer(p, v, space) \
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({ \
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smp_wmb(); \
|
|
(p) = (typeof(*v) __force space *)(v); \
|
|
})
|
|
|
|
|
|
/**
|
|
* 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.
|
|
*/
|
|
#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);
|
|
}
|
|
|
|
/*
|
|
* 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_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_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_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);
|
|
}
|
|
|
|
/* 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_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. Returns the value assigned.
|
|
*
|
|
* 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) \
|
|
p = (typeof(*v) __force __rcu *)(v)
|
|
|
|
static __always_inline bool __is_kfree_rcu_offset(unsigned long offset)
|
|
{
|
|
return offset < 4096;
|
|
}
|
|
|
|
static __always_inline
|
|
void __kfree_rcu(struct rcu_head *head, unsigned long offset)
|
|
{
|
|
typedef void (*rcu_callback)(struct rcu_head *);
|
|
|
|
BUILD_BUG_ON(!__builtin_constant_p(offset));
|
|
|
|
/* See the kfree_rcu() header comment. */
|
|
BUILD_BUG_ON(!__is_kfree_rcu_offset(offset));
|
|
|
|
call_rcu(head, (rcu_callback)offset);
|
|
}
|
|
|
|
/**
|
|
* 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().
|
|
*/
|
|
#define kfree_rcu(ptr, rcu_head) \
|
|
__kfree_rcu(&((ptr)->rcu_head), offsetof(typeof(*(ptr)), rcu_head))
|
|
|
|
#endif /* __LINUX_RCUPDATE_H */
|