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* Read-Copy Update mechanism for mutual exclusion (RT implementation)
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 2 of the License, or
* (at your option) any later version.
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* GNU General Public License for more details.
* You should have received a copy of the GNU General Public License
* along with this program; if not, write to the Free Software
* Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
* Copyright (C) IBM Corporation, 2006
* Author: Paul McKenney <>
* Based on the original work by Paul McKenney <>
* and inputs from Rusty Russell, Andrea Arcangeli and Andi Kleen.
* Papers:
* (OLS2001)
* For detailed explanation of Read-Copy Update mechanism see -
* Documentation/RCU
#include <linux/cache.h>
#include <linux/spinlock.h>
#include <linux/threads.h>
#include <linux/smp.h>
#include <linux/cpumask.h>
#include <linux/seqlock.h>
extern void rcu_qsctr_inc(int cpu);
static inline void rcu_bh_qsctr_inc(int cpu) { }
* Someone might want to pass call_rcu_bh as a function pointer.
* So this needs to just be a rename and not a macro function.
* (no parentheses)
#define call_rcu_bh call_rcu
* call_rcu_sched - Queue RCU callback for invocation after sched grace period.
* @head: structure to be used for queueing the RCU updates.
* @func: actual update function to be invoked after the grace period
* The update function will be invoked some time after a full
* synchronize_sched()-style grace period elapses, in other words after
* all currently executing preempt-disabled sections of code (including
* hardirq handlers, NMI handlers, and local_irq_save() blocks) have
* completed.
extern void call_rcu_sched(struct rcu_head *head,
void (*func)(struct rcu_head *head));
extern void __rcu_read_lock(void) __acquires(RCU);
extern void __rcu_read_unlock(void) __releases(RCU);
extern int rcu_pending(int cpu);
extern int rcu_needs_cpu(int cpu);
#define __rcu_read_lock_bh() { rcu_read_lock(); local_bh_disable(); }
#define __rcu_read_unlock_bh() { local_bh_enable(); rcu_read_unlock(); }
extern void __synchronize_sched(void);
extern void __rcu_init(void);
extern void rcu_init_sched(void);
extern void rcu_check_callbacks(int cpu, int user);
extern void rcu_restart_cpu(int cpu);
extern long rcu_batches_completed(void);
* Return the number of RCU batches processed thus far. Useful for debug
* and statistic. The _bh variant is identifcal to straight RCU
static inline long rcu_batches_completed_bh(void)
return rcu_batches_completed();
struct rcupreempt_trace;
extern long *rcupreempt_flipctr(int cpu);
extern long rcupreempt_data_completed(void);
extern int rcupreempt_flip_flag(int cpu);
extern int rcupreempt_mb_flag(int cpu);
extern char *rcupreempt_try_flip_state_name(void);
extern struct rcupreempt_trace *rcupreempt_trace_cpu(int cpu);
struct softirq_action;
extern void rcu_enter_nohz(void);
extern void rcu_exit_nohz(void);
# define rcu_enter_nohz() do { } while (0)
# define rcu_exit_nohz() do { } while (0)
* A context switch is a grace period for rcupreempt synchronize_rcu()
* only during early boot, before the scheduler has been initialized.
* So, how the heck do we get a context switch? Well, if the caller
* invokes synchronize_rcu(), they are willing to accept a context
* switch, so we simply pretend that one happened.
* After boot, there might be a blocked or preempted task in an RCU
* read-side critical section, so we cannot then take the fastpath.
static inline int rcu_blocking_is_gp(void)
return num_online_cpus() == 1 && !rcu_scheduler_active;
#endif /* __LINUX_RCUPREEMPT_H */