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 4.19-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-4.19 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 | 6 ++++++
1 file changed, 6 insertions(+)
--- a/kernel/sched/membarrier.c
+++ b/kernel/sched/membarrier.c
@@ -34,6 +34,8 @@
| 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. */
@@ -64,6 +66,7 @@ static int membarrier_global_expedited(v
fallback = true;
}
+ mutex_lock(&membarrier_ipi_mutex);
cpus_read_lock();
for_each_online_cpu(cpu) {
struct task_struct *p;
@@ -104,6 +107,7 @@ 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;
}
@@ -144,6 +148,7 @@ static int membarrier_private_expedited(
fallback = true;
}
+ mutex_lock(&membarrier_ipi_mutex);
cpus_read_lock();
for_each_online_cpu(cpu) {
struct task_struct *p;
@@ -182,6 +187,7 @@ 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;
}
Patches currently in stable-queue which might be from torvalds@xxxxxxxxxxxxxxxxxxx are
queue-4.19/sched-membarrier-reduce-the-ability-to-hammer-on-sys_membarrier.patch
