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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 b9aafef744
commit 50fb4e17df
1 changed files with 9 additions and 0 deletions
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9
kernel/sched/membarrier.c
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@@ -162,6 +162,8 @@
| MEMBARRIER_PRIVATE_EXPEDITED_SYNC_CORE_BITMASK \
| MEMBARRIER_PRIVATE_EXPEDITED_RSEQ_BITMASK)
static DEFINE_MUTEX(membarrier_ipi_mutex);
static void ipi_mb(void *info)
{
smp_mb(); /* IPIs should be serializing but paranoid. */
@@ -259,6 +261,7 @@ static int membarrier_global_expedited(void)
if (!zalloc_cpumask_var(&tmpmask, GFP_KERNEL))
return -ENOMEM;
mutex_lock(&membarrier_ipi_mutex);
cpus_read_lock();
rcu_read_lock();
for_each_online_cpu(cpu) {
@@ -304,6 +307,8 @@ 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;
}
@@ -347,6 +352,7 @@ static int membarrier_private_expedited(int flags, int cpu_id)
if (cpu_id < 0 && !zalloc_cpumask_var(&tmpmask, GFP_KERNEL))
return -ENOMEM;
mutex_lock(&membarrier_ipi_mutex);
cpus_read_lock();
if (cpu_id >= 0) {
@@ -419,6 +425,7 @@ out:
* rq->curr modification in scheduler.
*/
smp_mb(); /* exit from system call is not a mb */
mutex_unlock(&membarrier_ipi_mutex);
return 0;
}
@@ -460,6 +467,7 @@ static int sync_runqueues_membarrier_state(struct mm_struct *mm)
* between threads which are users of @mm has its membarrier state
* updated.
*/
mutex_lock(&membarrier_ipi_mutex);
cpus_read_lock();
rcu_read_lock();
for_each_online_cpu(cpu) {
@@ -476,6 +484,7 @@ static int sync_runqueues_membarrier_state(struct mm_struct *mm)
free_cpumask_var(tmpmask);
cpus_read_unlock();
mutex_unlock(&membarrier_ipi_mutex);
return 0;
}