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authorJohn Stultz <john.stultz@linaro.org>2015-06-17 10:05:53 -0700
committerThomas Gleixner <tglx@linutronix.de>2015-06-18 09:27:02 +0200
commit906c55579a6360dd9ef5a3101bb2e3ae396dfb97 (patch)
treec105a14950a598af6aa9f2e9e74450a14a84443a /kernel/time
parenta9d20988ac7db47fec4510cefc966e876a4ce674 (diff)
downloadlinux-906c55579a6360dd9ef5a3101bb2e3ae396dfb97.tar.bz2
timekeeping: Copy the shadow-timekeeper over the real timekeeper last
The fix in d151832650ed9 (time: Move clock_was_set_seq update before updating shadow-timekeeper) was unfortunately incomplete. The main gist of that change was to do the shadow-copy update last, so that any state changes were properly duplicated, and we wouldn't accidentally have stale data in the shadow. Unfortunately in the main update_wall_time() logic, we update use the shadow-timekeeper to calculate the next update values, then while holding the lock, copy the shadow-timekeeper over, then call timekeeping_update() to do some additional bookkeeping, (skipping the shadow mirror). The bug with this is the additional bookkeeping isn't all read-only, and some changes timkeeper state. Thus we might then overwrite this state change on the next update. To avoid this problem, do the timekeeping_update() on the shadow-timekeeper prior to copying the full state over to the real-timekeeper. This avoids problems with both the clock_was_set_seq and next_leap_ktime being overwritten and possibly the fast-timekeepers as well. Many thanks to Prarit for his rigorous testing, which discovered this problem, along with Prarit and Daniel's work validating this fix. Reported-by: Prarit Bhargava <prarit@redhat.com> Tested-by: Prarit Bhargava <prarit@redhat.com> Tested-by: Daniel Bristot de Oliveira <bristot@redhat.com> Signed-off-by: John Stultz <john.stultz@linaro.org> Cc: Richard Cochran <richardcochran@gmail.com> Cc: Jan Kara <jack@suse.cz> Cc: Jiri Bohac <jbohac@suse.cz> Cc: Ingo Molnar <mingo@kernel.org> Link: http://lkml.kernel.org/r/1434560753-7441-1-git-send-email-john.stultz@linaro.org Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Diffstat (limited to 'kernel/time')
-rw-r--r--kernel/time/timekeeping.c3
1 files changed, 2 insertions, 1 deletions
diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c
index 5d67ffb7e317..30b7a409bf1e 100644
--- a/kernel/time/timekeeping.c
+++ b/kernel/time/timekeeping.c
@@ -1853,8 +1853,9 @@ void update_wall_time(void)
* memcpy under the tk_core.seq against one before we start
* updating.
*/
+ timekeeping_update(tk, clock_set);
memcpy(real_tk, tk, sizeof(*tk));
- timekeeping_update(real_tk, clock_set);
+ /* The memcpy must come last. Do not put anything here! */
write_seqcount_end(&tk_core.seq);
out:
raw_spin_unlock_irqrestore(&timekeeper_lock, flags);