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| author | John Stultz <john.stultz@linaro.org> | 2015-06-17 10:05:53 -0700 |
|---|---|---|
| committer | Thomas Gleixner <tglx@linutronix.de> | 2015-06-18 09:27:02 +0200 |
| commit | 906c55579a6360dd9ef5a3101bb2e3ae396dfb97 (patch) | |
| tree | c105a14950a598af6aa9f2e9e74450a14a84443a /kernel/time | |
| parent | a9d20988ac7db47fec4510cefc966e876a4ce674 (diff) | |
| download | linux-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.c | 3 |
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); |