diff options
| author | Neal Cardwell <ncardwell@google.com> | 2012-03-27 15:09:37 -0400 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2012-04-22 16:21:25 -0700 |
| commit | 2ca8877b566438c293e4e54d39c959a9a847a77b (patch) | |
| tree | 0183b4574853e9e717c6398c6f84a482d18acb45 /kernel | |
| parent | 8bc3db1c0794236cc21580fb3afac6de3ff27849 (diff) | |
nohz: Fix stale jiffies update in tick_nohz_restart()
commit 6f103929f8979d2638e58d7f7fda0beefcb8ee7e upstream.
Fix tick_nohz_restart() to not use a stale ktime_t "now" value when
calling tick_do_update_jiffies64(now).
If we reach this point in the loop it means that we crossed a tick
boundary since we grabbed the "now" timestamp, so at this point "now"
refers to a time in the old jiffy, so using the old value for "now" is
incorrect, and is likely to give us a stale jiffies value.
In particular, the first time through the loop the
tick_do_update_jiffies64(now) call is always a no-op, since the
caller, tick_nohz_restart_sched_tick(), will have already called
tick_do_update_jiffies64(now) with that "now" value.
Note that tick_nohz_stop_sched_tick() already uses the correct
approach: when we notice we cross a jiffy boundary, grab a new
timestamp with ktime_get(), and *then* update jiffies.
Signed-off-by: Neal Cardwell <ncardwell@google.com>
Cc: Ben Segall <bsegall@google.com>
Cc: Ingo Molnar <mingo@elte.hu>
Link: http://lkml.kernel.org/r/1332875377-23014-1-git-send-email-ncardwell@google.com
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'kernel')
| -rw-r--r-- | kernel/time/tick-sched.c | 4 |
1 files changed, 2 insertions, 2 deletions
diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c index d5097c44b407..c473ce246cb7 100644 --- a/kernel/time/tick-sched.c +++ b/kernel/time/tick-sched.c @@ -484,9 +484,9 @@ static void tick_nohz_restart(struct tick_sched *ts, ktime_t now) hrtimer_get_expires(&ts->sched_timer), 0)) break; } - /* Update jiffies and reread time */ - tick_do_update_jiffies64(now); + /* Reread time and update jiffies */ now = ktime_get(); + tick_do_update_jiffies64(now); } } |