* [PATCH] timekeeping: Copy the shadow-timekeeper over the real timekeeper last
@ 2015-06-17 17:05 John Stultz
2015-06-18 7:31 ` [tip:timers/core] " tip-bot for John Stultz
0 siblings, 1 reply; 2+ messages in thread
From: John Stultz @ 2015-06-17 17:05 UTC (permalink / raw)
To: lkml
Cc: John Stultz, Prarit Bhargava, Daniel Bristot de Oliveira,
Richard Cochran, Jan Kara, Jiri Bohac, Ingo Molnar,
Thomas Gleixner
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.
Cc: Prarit Bhargava <prarit@redhat.com>
Cc: Daniel Bristot de Oliveira <bristot@redhat.com>
Cc: Richard Cochran <richardcochran@gmail.com>
Cc: Jan Kara <jack@suse.cz>
Cc: Jiri Bohac <jbohac@suse.cz>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
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>
---
(This patch applies to tip/timers/core)
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);
--
1.9.1
^ permalink raw reply related [flat|nested] 2+ messages in thread
* [tip:timers/core] timekeeping: Copy the shadow-timekeeper over the real timekeeper last
2015-06-17 17:05 [PATCH] timekeeping: Copy the shadow-timekeeper over the real timekeeper last John Stultz
@ 2015-06-18 7:31 ` tip-bot for John Stultz
0 siblings, 0 replies; 2+ messages in thread
From: tip-bot for John Stultz @ 2015-06-18 7:31 UTC (permalink / raw)
To: linux-tip-commits
Cc: jack, jbohac, tglx, bristot, mingo, richardcochran, john.stultz,
hpa, linux-kernel, prarit
Commit-ID: 906c55579a6360dd9ef5a3101bb2e3ae396dfb97
Gitweb: http://git.kernel.org/tip/906c55579a6360dd9ef5a3101bb2e3ae396dfb97
Author: John Stultz <john.stultz@linaro.org>
AuthorDate: Wed, 17 Jun 2015 10:05:53 -0700
Committer: Thomas Gleixner <tglx@linutronix.de>
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@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>
---
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);
^ permalink raw reply related [flat|nested] 2+ messages in thread
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