timers: Fix data race in timer_stats_account_timer()
timer_stats_account_timer() reads timer->start_site, then checks it for NULL and then re-reads it again, while timer_stats_timer_clear_start_info() can concurrently reset timer->start_site to NULL. This should not lead to crashes, but can double number of entries in timer stats as start_site is used during comparison, the doubled entries will have unuseful NULL start_site. Read timer->start_site only once in timer_stats_account_timer(). The data race was found with KernelThreadSanitizer (KTSAN). Signed-off-by: Dmitry Vyukov <dvyukov@google.com> Cc: andreyknvl@google.com Cc: glider@google.com Cc: kcc@google.com Cc: ktsan@googlegroups.com Cc: john.stultz@linaro.org Link: http://lkml.kernel.org/r/1442584463-69553-1-git-send-email-dvyukov@google.com Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
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@ -461,10 +461,17 @@ void __timer_stats_timer_set_start_info(struct timer_list *timer, void *addr)
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static void timer_stats_account_timer(struct timer_list *timer)
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static void timer_stats_account_timer(struct timer_list *timer)
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{
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{
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if (likely(!timer->start_site))
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void *site;
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/*
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* start_site can be concurrently reset by
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* timer_stats_timer_clear_start_info()
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*/
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site = READ_ONCE(timer->start_site);
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if (likely(!site))
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return;
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return;
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timer_stats_update_stats(timer, timer->start_pid, timer->start_site,
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timer_stats_update_stats(timer, timer->start_pid, site,
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timer->function, timer->start_comm,
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timer->function, timer->start_comm,
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timer->flags);
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timer->flags);
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}
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}
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