Messages in this thread Patch in this message | | | From | Vincent Donnefort <> | Subject | [PATCH] sched/core: Mitigate race cpus_share_cache()/update_top_cache_domain() | Date | Thu, 4 Nov 2021 17:51:20 +0000 |
| |
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> Reviewed-by: Valentin Schneider <valentin.schneider@arm.com>
diff --git a/kernel/sched/core.c b/kernel/sched/core.c index f2611b9cf503..f5ca15cdcff4 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -3726,6 +3726,9 @@ 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); } -- 2.25.1
| |