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authorVincent Donnefort <vincent.donnefort@arm.com>2021-11-04 17:51:20 +0000
committerPeter Zijlstra <peterz@infradead.org>2021-11-11 13:09:32 +0100
commit42dc938a590c96eeb429e1830123fef2366d9c80 (patch)
tree95faa20c9b60056b3ff506980e1580a56e46052a /kernel
parentce2612b6706b4d0a70732795253722e3bd4ed953 (diff)
sched/core: Mitigate race cpus_share_cache()/update_top_cache_domain()
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@mediatek.com> Signed-off-by: Vincent Donnefort <vincent.donnefort@arm.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Reviewed-by: Valentin Schneider <valentin.schneider@arm.com> Reviewed-by: Vincent Guittot <vincent.guittot@linaro.org> Link: https://lore.kernel.org/r/20211104175120.857087-1-vincent.donnefort@arm.com
Diffstat (limited to 'kernel')
-rw-r--r--kernel/sched/core.c3
1 files changed, 3 insertions, 0 deletions
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 523fd602ea90..cec173a5fc5e 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -3726,6 +3726,9 @@ out:
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);
}