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Commit ab4720ec authored by Dipankar Sarma's avatar Dipankar Sarma Committed by Linus Torvalds
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[PATCH] add rcu_barrier() synchronization point 



This introduces a new interface - rcu_barrier() which waits until all
the RCUs queued until this call have been completed.

Reiser4 needs this, because we do more than just freeing memory object
in our RCU callback: we also remove it from the list hanging off
super-block.  This means, that before freeing reiser4-specific portion
of super-block (during umount) we have to wait until all pending RCU
callbacks are executed.

The only change of reiser4 made to the original patch, is exporting of
rcu_barrier().

Cc: Hans Reiser <reiser@namesys.com>
Cc: Vladimir V. Saveliev <vs@namesys.com>
Signed-off-by: default avatarAndrew Morton <akpm@osdl.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@osdl.org>
parent 85b87242

include/linux/rcupdate.h

+2 −0
Original line number Diff line number Diff line
@@ -100,6 +100,7 @@ struct rcu_data { 
	struct rcu_head *donelist;

	struct rcu_head **donetail;

	int cpu;

	struct rcu_head barrier;

};



DECLARE_PER_CPU(struct rcu_data, rcu_data);
@@ -285,6 +286,7 @@ extern void FASTCALL(call_rcu_bh(struct rcu_head *head, 
extern __deprecated_for_modules void synchronize_kernel(void);

extern void synchronize_rcu(void);

void synchronize_idle(void);

extern void rcu_barrier(void);



#endif /* __KERNEL__ */

#endif /* __LINUX_RCUPDATE_H */

kernel/rcupdate.c

+41 −0
Original line number Diff line number Diff line
@@ -116,6 +116,10 @@ void fastcall call_rcu(struct rcu_head *head, 
	local_irq_restore(flags);

}



static atomic_t rcu_barrier_cpu_count;

static struct semaphore rcu_barrier_sema;

static struct completion rcu_barrier_completion;



/**

 * call_rcu_bh - Queue an RCU for invocation after a quicker grace period.

 * @head: structure to be used for queueing the RCU updates.
@@ -162,6 +166,42 @@ long rcu_batches_completed(void) 
	return rcu_ctrlblk.completed;

}



static void rcu_barrier_callback(struct rcu_head *notused)

{

	if (atomic_dec_and_test(&rcu_barrier_cpu_count))

		complete(&rcu_barrier_completion);

}



/*

 * Called with preemption disabled, and from cross-cpu IRQ context.

 */

static void rcu_barrier_func(void *notused)

{

	int cpu = smp_processor_id();

	struct rcu_data *rdp = &per_cpu(rcu_data, cpu);

	struct rcu_head *head;



	head = &rdp->barrier;

	atomic_inc(&rcu_barrier_cpu_count);

	call_rcu(head, rcu_barrier_callback);

}



/**

 * rcu_barrier - Wait until all the in-flight RCUs are complete.

 */

void rcu_barrier(void)

{

	BUG_ON(in_interrupt());

	/* Take cpucontrol semaphore to protect against CPU hotplug */

	down(&rcu_barrier_sema);

	init_completion(&rcu_barrier_completion);

	atomic_set(&rcu_barrier_cpu_count, 0);

	on_each_cpu(rcu_barrier_func, NULL, 0, 1);

	wait_for_completion(&rcu_barrier_completion);

	up(&rcu_barrier_sema);

}

EXPORT_SYMBOL_GPL(rcu_barrier);



/*

 * Invoke the completed RCU callbacks. They are expected to be in

 * a per-cpu list.
@@ -457,6 +497,7 @@ static struct notifier_block __devinitdata rcu_nb = { 
 */

void __init rcu_init(void)

{

	sema_init(&rcu_barrier_sema, 1);

	rcu_cpu_notify(&rcu_nb, CPU_UP_PREPARE,

			(void *)(long)smp_processor_id());

	/* Register notifier for non-boot CPUs */