From b1ef24e781682688df009602e81718ac9a868cce Mon Sep 17 00:00:00 2001
From: Linus Torvalds <torvalds@linuxfoundation.org>
Date: Sun, 4 Feb 2024 15:25:12 +0000
Subject: [PATCH] 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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
kernel/sched/membarrier.c | 6 ++++++
1 file changed, 6 insertions(+)
diff --git a/kernel/sched/membarrier.c b/kernel/sched/membarrier.c
index 0c5be7ebb1dca..08b16d20c85bb 100644
--- a/kernel/sched/membarrier.c
+++ b/kernel/sched/membarrier.c
@@ -161,6 +161,9 @@
| MEMBARRIER_PRIVATE_EXPEDITED_SYNC_CORE_BITMASK \
| MEMBARRIER_PRIVATE_EXPEDITED_RSEQ_BITMASK)
+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. */
@@ -258,6 +261,7 @@ 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) {
@@ -346,6 +350,7 @@ 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) {
@@ -459,6 +464,7 @@ 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) {
--
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