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authorNeal Cardwell <ncardwell@google.com>2012-03-27 15:09:37 -0400
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2012-04-22 16:21:25 -0700
commit2ca8877b566438c293e4e54d39c959a9a847a77b (patch)
tree0183b4574853e9e717c6398c6f84a482d18acb45 /kernel
parent8bc3db1c0794236cc21580fb3afac6de3ff27849 (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.c4
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);
}
}