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From 2441a64070b85c14eecc3728cc87e883f953f265 Mon Sep 17 00:00:00 2001
From: Linus Torvalds <torvalds@linuxfoundation.org>
Date: Sun, 4 Feb 2024 15:25:12 +0000
Subject: 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: 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 | 9 +++++++++
1 file changed, 9 insertions(+)
diff --git a/kernel/sched/membarrier.c b/kernel/sched/membarrier.c
index b5add64d9698..0b5e3e520bf6 100644
--- a/kernel/sched/membarrier.c
+++ b/kernel/sched/membarrier.c
@@ -161,6 +161,8 @@
| 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. */
@@ -258,6 +260,7 @@ 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) {
@@ -303,6 +306,8 @@ 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;
}
@@ -346,6 +351,7 @@ static int membarrier_private_expedited(int flags, int cpu_id)
if (cpu_id < 0 && !zalloc_cpumask_var(&tmpmask, GFP_KERNEL))
return -ENOMEM;
+ mutex_lock(&membarrier_ipi_mutex);
cpus_read_lock();
if (cpu_id >= 0) {
@@ -418,6 +424,7 @@ static int membarrier_private_expedited(int flags, int cpu_id)
* rq->curr modification in scheduler.
*/
smp_mb(); /* exit from system call is not a mb */
+ mutex_unlock(&membarrier_ipi_mutex);
return 0;
}
@@ -459,6 +466,7 @@ 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) {
@@ -475,6 +483,7 @@ static int sync_runqueues_membarrier_state(struct mm_struct *mm)
free_cpumask_var(tmpmask);
cpus_read_unlock();
+ mutex_unlock(&membarrier_ipi_mutex);
return 0;
}
--
2.25.1
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