From 3cd139875e9a7688b3fc715264032620812a5fa3 Mon Sep 17 00:00:00 2001 From: Linus Torvalds 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 Acked-by: Borislav Petkov Fixes: 22e4ebb97582 ("membarrier: Provide expedited private command") Fixes: c5f58bd58f43 ("membarrier: Provide GLOBAL_EXPEDITED command") Signed-off-by: Linus Torvalds [ converted to explicit mutex_*() calls - cleanup.h is not in this stable branch - gregkh ] Signed-off-by: Greg Kroah-Hartman --- kernel/sched/membarrier.c | 6 ++++++ 1 file changed, 6 insertions(+) diff --git a/kernel/sched/membarrier.c b/kernel/sched/membarrier.c index dd27e632b1ba..9049ca636e17 100644 --- 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(void) 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(void) * 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(int flags) 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(int flags) * rq->curr modification in scheduler. */ smp_mb(); /* exit from system call is not a mb */ + mutex_unlock(&membarrier_ipi_mutex); return 0; }