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Commit 99744387 authored by Vincent Donnefort's avatar Vincent Donnefort Committed by Greg Kroah-Hartman
Browse files

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: 518cd623 ("sched: Only queue remote wakeups when crossing cache boundaries")
Reported-by: default avatarJing-Ting Wu <jing-ting.wu@mediatek.com>
Signed-off-by: default avatarVincent Donnefort <vincent.donnefort@arm.com>
Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: default avatarValentin Schneider <valentin.schneider@arm.com>
Reviewed-by: default avatarVincent Guittot <vincent.guittot@linaro.org>
Link: https://lore.kernel.org/r/20211104175120.857087-1-vincent.donnefort@arm.com


Signed-off-by: default avatarSasha Levin <sashal@kernel.org>
parent 0f3a44e0

kernel/sched/core.c

+3 −0
Original line number Diff line number Diff line
@@ -1875,6 +1875,9 @@ 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 */