Commit 944d5fe5 authored by Linus Torvalds's avatar Linus Torvalds Committed by Linus Torvalds
Browse files

sched/membarrier: reduce the ability to hammer on sys_membarrier 



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.

Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
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>
parent b401b621

kernel/sched/membarrier.c

+6 −0
Original line number Diff line number Diff line
@@ -162,6 +162,9 @@ 
	| MEMBARRIER_PRIVATE_EXPEDITED_RSEQ_BITMASK			\

	| MEMBARRIER_CMD_GET_REGISTRATIONS)



static DEFINE_MUTEX(membarrier_ipi_mutex);

#define SERIALIZE_IPI() guard(mutex)(&membarrier_ipi_mutex)



static void ipi_mb(void *info)

{

	smp_mb();	/* IPIs should be serializing but paranoid. */
@@ -259,6 +262,7 @@ static int membarrier_global_expedited(void) 
	if (!zalloc_cpumask_var(&tmpmask, GFP_KERNEL))

		return -ENOMEM;



	SERIALIZE_IPI();

	cpus_read_lock();

	rcu_read_lock();

	for_each_online_cpu(cpu) {
@@ -347,6 +351,7 @@ static int membarrier_private_expedited(int flags, int cpu_id) 
	if (cpu_id < 0 && !zalloc_cpumask_var(&tmpmask, GFP_KERNEL))

		return -ENOMEM;



	SERIALIZE_IPI();

	cpus_read_lock();



	if (cpu_id >= 0) {
@@ -460,6 +465,7 @@ static int sync_runqueues_membarrier_state(struct mm_struct *mm) 
	 * between threads which are users of @mm has its membarrier state

	 * updated.

	 */

	SERIALIZE_IPI();

	cpus_read_lock();

	rcu_read_lock();

	for_each_online_cpu(cpu) {