Commit-ID: 3ed769bdb2a2484fd7f9f7f3047413053aacbe21
Gitweb: http://git.kernel.org/tip/3ed769bdb2a2484fd7f9f7f3047413053aacbe21
Author: Dmitry Vyukov <dvyukov@xxxxxxxxxx>
AuthorDate: Fri, 18 Sep 2015 15:54:23 +0200
Committer: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
CommitDate: Tue, 22 Sep 2015 15:43:18 +0200
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@xxxxxxxxxx>
Cc: andreyknvl@xxxxxxxxxx
Cc: glider@xxxxxxxxxx
Cc: kcc@xxxxxxxxxx
Cc: ktsan@xxxxxxxxxxxxxxxx
Cc: john.stultz@xxxxxxxxxx
Link: http://lkml.kernel.org/r/1442584463-69553-1-git-send-email-dvyukov@xxxxxxxxxx
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
---
kernel/time/timer.c | 11 +++++++++--
1 file changed, 9 insertions(+), 2 deletions(-)
diff --git a/kernel/time/timer.c b/kernel/time/timer.c
index 84190f0..d3f5e92 100644
--- a/kernel/time/timer.c
+++ b/kernel/time/timer.c
@@ -461,10 +461,17 @@ void __timer_stats_timer_set_start_info(struct timer_list *timer, void *addr)
static void timer_stats_account_timer(struct timer_list *timer)
{
- if (likely(!timer->start_site))
+ void *site;
+
+ /*
+ * start_site can be concurrently reset by
+ * timer_stats_timer_clear_start_info()
+ */
+ site = READ_ONCE(timer->start_site);
+ if (likely(!site))
return;
- timer_stats_update_stats(timer, timer->start_pid, timer->start_site,
+ timer_stats_update_stats(timer, timer->start_pid, site,
timer->function, timer->start_comm,
timer->flags);
}
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