4.19-stable review patch. If anyone has any objections, please let me know.
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From: Linus Torvalds torvalds@linuxfoundation.org
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: Mathieu Desnoyers mathieu.desnoyers@efficios.com Acked-by: Borislav Petkov bp@alien8.de Fixes: 22e4ebb97582 ("membarrier: Provide expedited private command") Fixes: c5f58bd58f43 ("membarrier: Provide GLOBAL_EXPEDITED command") Signed-off-by: Linus Torvalds torvalds@linux-foundation.org [ converted to explicit mutex_*() calls - cleanup.h is not in this stable branch - gregkh ] Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- kernel/sched/membarrier.c | 6 ++++++ 1 file changed, 6 insertions(+)
--- a/kernel/sched/membarrier.c +++ b/kernel/sched/membarrier.c @@ -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(v 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(v * 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( 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( * rq->curr modification in scheduler. */ smp_mb(); /* exit from system call is not a mb */ + mutex_unlock(&membarrier_ipi_mutex);
return 0; }