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 6.6-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-6.6 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>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
kernel/sched/membarrier.c | 6 ++++++
1 file changed, 6 insertions(+)
--- a/kernel/sched/membarrier.c
+++ b/kernel/sched/membarrier.c
@@ -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(v
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(
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_sta
* 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) {
Patches currently in stable-queue which might be from torvalds@xxxxxxxxxxxxxxxxxxx are
queue-6.6/sched-membarrier-reduce-the-ability-to-hammer-on-sys_membarrier.patch
