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Commit 3cd13987 authored by Linus Torvalds's avatar Linus Torvalds Committed by Greg Kroah-Hartman
Browse files

sched/membarrier: reduce the ability to hammer on sys_membarrier 



commit 944d5fe50f3f03daacfea16300e656a1691c4a23 upstream.

On some systems, sys_membarrier can be very expensive, causing overall
slowdowns for everything.  So put a lock on the path in order to
serialize the accesses to prevent the ability for this to be called at
too high of a frequency and saturate the machine.

Reviewed-and-tested-by: default avatarMathieu Desnoyers <mathieu.desnoyers@efficios.com>
Acked-by: default avatarBorislav Petkov <bp@alien8.de>
Fixes: 22e4ebb9 ("membarrier: Provide expedited private command")
Fixes: c5f58bd5 ("membarrier: Provide GLOBAL_EXPEDITED command")
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
[ converted to explicit mutex_*() calls - cleanup.h is not in this stable
  branch - gregkh ]
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent 1e8c1c2a

kernel/sched/membarrier.c

+6 −0
Original line number Diff line number Diff line
@@ -34,6 +34,8 @@ 
	| MEMBARRIER_CMD_REGISTER_PRIVATE_EXPEDITED			\

	| MEMBARRIER_PRIVATE_EXPEDITED_SYNC_CORE_BITMASK)



static DEFINE_MUTEX(membarrier_ipi_mutex);



static void ipi_mb(void *info)

{

	smp_mb();	/* IPIs should be serializing but paranoid. */
@@ -64,6 +66,7 @@ static int membarrier_global_expedited(void) 
		fallback = true;

	}



	mutex_lock(&membarrier_ipi_mutex);

	cpus_read_lock();

	for_each_online_cpu(cpu) {

		struct task_struct *p;
@@ -104,6 +107,7 @@ static int membarrier_global_expedited(void) 
	 * rq->curr modification in scheduler.

	 */

	smp_mb();	/* exit from system call is not a mb */

	mutex_unlock(&membarrier_ipi_mutex);

	return 0;

}
@@ -144,6 +148,7 @@ static int membarrier_private_expedited(int flags) 
		fallback = true;

	}



	mutex_lock(&membarrier_ipi_mutex);

	cpus_read_lock();

	for_each_online_cpu(cpu) {

		struct task_struct *p;
@@ -182,6 +187,7 @@ static int membarrier_private_expedited(int flags) 
	 * rq->curr modification in scheduler.

	 */

	smp_mb();	/* exit from system call is not a mb */

	mutex_unlock(&membarrier_ipi_mutex);



	return 0;

}