Commit-ID: 906c55579a6360dd9ef5a3101bb2e3ae396dfb97 Gitweb: http://git.kernel.org/tip/906c55579a6360dd9ef5a3101bb2e3ae396dfb97 Author: John Stultz <john.stultz@xxxxxxxxxx> AuthorDate: Wed, 17 Jun 2015 10:05:53 -0700 Committer: Thomas Gleixner <tglx@xxxxxxxxxxxxx> CommitDate: Thu, 18 Jun 2015 09:27:02 +0200 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@xxxxxxxxxx> Tested-by: Prarit Bhargava <prarit@xxxxxxxxxx> Tested-by: Daniel Bristot de Oliveira <bristot@xxxxxxxxxx> Signed-off-by: John Stultz <john.stultz@xxxxxxxxxx> Cc: Richard Cochran <richardcochran@xxxxxxxxx> Cc: Jan Kara <jack@xxxxxxx> Cc: Jiri Bohac <jbohac@xxxxxxx> Cc: Ingo Molnar <mingo@xxxxxxxxxx> Link: http://lkml.kernel.org/r/1434560753-7441-1-git-send-email-john.stultz@xxxxxxxxxx Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx> --- kernel/time/timekeeping.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c index 5d67ffb..30b7a40 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); -- To unsubscribe from this list: send the line "unsubscribe linux-tip-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
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