Messages in this thread | | | From | Shinichiro Kawasaki <> | Subject | Re: [PATCH] sched/core: Mitigate race cpus_share_cache()/update_top_cache_domain() | Date | Mon, 15 Nov 2021 10:46:02 +0000 |
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On Nov 04, 2021 / 17:51, Vincent Donnefort wrote: > 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 >
Oh, this is the exactly same fix as I posted before [1]. It is a little bit sad that my post did not get reviewed. Anyway, good to see the issue fixed. Thanks.
[1] https://lore.kernel.org/all/20211029005618.773579-1-shinichiro.kawasaki@wdc.com/
-- Best Regards, Shin'ichiro Kawasaki
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