From: Vincent Donnefort vincent.donnefort@arm.com
[ 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@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 Signed-off-by: Sasha Levin sashal@kernel.org --- kernel/sched/core.c | 3 +++ 1 file changed, 3 insertions(+)
diff --git a/kernel/sched/core.c b/kernel/sched/core.c index bc8ff11e60242..e456cce772a3a 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -2650,6 +2650,9 @@ 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); }