This is a note to let you know that I've just added the patch titled
sched/core: Mitigate race cpus_share_cache()/update_top_cache_domain()
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-core-mitigate-race-cpus_share_cache-update_top.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.
commit d7fd604052b2e8817592daae67a460fee0ddefa6
Author: Vincent Donnefort <vincent.donnefort@xxxxxxx>
Date: Thu Nov 4 17:51:20 2021 +0000
sched/core: Mitigate race cpus_share_cache()/update_top_cache_domain()
[ Upstream commit 42dc938a590c96eeb429e1830123fef2366d9c80 ]
Nothing protects the access to the per_cpu variable sd_llc_id. When testing
the same CPU (i.e. this_cpu == that_cpu), a race condition exists with
update_top_cache_domain(). One scenario being:
CPU1 CPU2
==================================================================
per_cpu(sd_llc_id, CPUX) => 0
partition_sched_domains_locked()
detach_destroy_domains()
cpus_share_cache(CPUX, CPUX) update_top_cache_domain(CPUX)
per_cpu(sd_llc_id, CPUX) => 0
per_cpu(sd_llc_id, CPUX) = CPUX
per_cpu(sd_llc_id, CPUX) => CPUX
return false
ttwu_queue_cond() wouldn't catch smp_processor_id() == cpu and the result
is a warning triggered from ttwu_queue_wakelist().
Avoid a such race in cpus_share_cache() by always returning true when
this_cpu == that_cpu.
Fixes: 518cd6234178 ("sched: Only queue remote wakeups when crossing cache boundaries")
Reported-by: Jing-Ting Wu <jing-ting.wu@xxxxxxxxxxxx>
Signed-off-by: Vincent Donnefort <vincent.donnefort@xxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Reviewed-by: Valentin Schneider <valentin.schneider@xxxxxxx>
Reviewed-by: Vincent Guittot <vincent.guittot@xxxxxxxxxx>
Link: https://lore.kernel.org/r/20211104175120.857087-1-vincent.donnefort@xxxxxxx
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 5dc43d37e6a2b..f8ca0738d729e 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -2482,6 +2482,9 @@ void wake_up_if_idle(int cpu)
bool cpus_share_cache(int this_cpu, int that_cpu)
{
+ if (this_cpu == that_cpu)
+ return true;
+
return per_cpu(sd_llc_id, this_cpu) == per_cpu(sd_llc_id, that_cpu);
}
#endif /* CONFIG_SMP */
