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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: 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>
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 0a962f2fba
commit b6a2a9cbb6
1 changed files with 6 additions and 0 deletions
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6
kernel/sched/membarrier.c
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@ -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) {