This is a note to let you know that I've just added the patch titled
sched/membarrier: reduce the ability to hammer on sys_membarrier
to the 5.4-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
sched-membarrier-reduce-the-ability-to-hammer-on-sys_membarrier.patch
and it can be found in the queue-5.4 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From 944d5fe50f3f03daacfea16300e656a1691c4a23 Mon Sep 17 00:00:00 2001
From: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxx>
Date: Sun, 4 Feb 2024 15:25:12 +0000
Subject: sched/membarrier: reduce the ability to hammer on sys_membarrier
From: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxx>
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@xxxxxxxxxxxx>
Acked-by: Borislav Petkov <bp@xxxxxxxxx>
Fixes: 22e4ebb97582 ("membarrier: Provide expedited private command")
Fixes: c5f58bd58f43 ("membarrier: Provide GLOBAL_EXPEDITED command")
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
[ converted to explicit mutex_*() calls - cleanup.h is not in this stable
branch - gregkh ]
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
kernel/sched/membarrier.c | 9 +++++++++
1 file changed, 9 insertions(+)
--- a/kernel/sched/membarrier.c
+++ b/kernel/sched/membarrier.c
@@ -25,6 +25,8 @@
| 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. */
@@ -97,6 +99,7 @@ static int membarrier_global_expedited(v
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) {
@@ -143,6 +146,8 @@ 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;
}
@@ -178,6 +183,7 @@ static int membarrier_private_expedited(
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) {
@@ -212,6 +218,7 @@ 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;
}
@@ -253,6 +260,7 @@ static int sync_runqueues_membarrier_sta
* 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) {
@@ -269,6 +277,7 @@ static int sync_runqueues_membarrier_sta
free_cpumask_var(tmpmask);
cpus_read_unlock();
+ mutex_unlock(&membarrier_ipi_mutex);
return 0;
}
Patches currently in stable-queue which might be from torvalds@xxxxxxxxxxxxxxxxxxx are
queue-5.4/sched-membarrier-reduce-the-ability-to-hammer-on-sys_membarrier.patch
