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sched/membarrier: reduce the ability to hammer on sys_membarrier

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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: 22e4ebb975 ("membarrier: Provide expedited private command")
Fixes: c5f58bd58f ("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>
This commit is contained in:
Linus Torvalds
2024-02-04 15:25:12 +00:00
committed by Greg Kroah-Hartman
parent 1e8c1c2a92
commit 3cd139875e
1 changed files with 6 additions and 0 deletions
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6
kernel/sched/membarrier.c
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@@ -34,6 +34,8 @@
| MEMBARRIER_CMD_REGISTER_PRIVATE_EXPEDITED \ | MEMBARRIER_CMD_REGISTER_PRIVATE_EXPEDITED \
| MEMBARRIER_PRIVATE_EXPEDITED_SYNC_CORE_BITMASK) | MEMBARRIER_PRIVATE_EXPEDITED_SYNC_CORE_BITMASK)
static DEFINE_MUTEX(membarrier_ipi_mutex);
static void ipi_mb(void *info) static void ipi_mb(void *info)
{ {
smp_mb(); /* IPIs should be serializing but paranoid. */ smp_mb(); /* IPIs should be serializing but paranoid. */
@@ -64,6 +66,7 @@ static int membarrier_global_expedited(void)
fallback = true; fallback = true;
} }
mutex_lock(&membarrier_ipi_mutex);
cpus_read_lock(); cpus_read_lock();
for_each_online_cpu(cpu) { for_each_online_cpu(cpu) {
struct task_struct *p; struct task_struct *p;
@@ -104,6 +107,7 @@ static int membarrier_global_expedited(void)
* rq->curr modification in scheduler. * rq->curr modification in scheduler.
*/ */
smp_mb(); /* exit from system call is not a mb */ smp_mb(); /* exit from system call is not a mb */
mutex_unlock(&membarrier_ipi_mutex);
return 0; return 0;
} }
@@ -144,6 +148,7 @@ static int membarrier_private_expedited(int flags)
fallback = true; fallback = true;
} }
mutex_lock(&membarrier_ipi_mutex);
cpus_read_lock(); cpus_read_lock();
for_each_online_cpu(cpu) { for_each_online_cpu(cpu) {
struct task_struct *p; struct task_struct *p;
@@ -182,6 +187,7 @@ static int membarrier_private_expedited(int flags)
* rq->curr modification in scheduler. * rq->curr modification in scheduler.
*/ */
smp_mb(); /* exit from system call is not a mb */ smp_mb(); /* exit from system call is not a mb */
mutex_unlock(&membarrier_ipi_mutex);
return 0; return 0;
} }