nohz: Fix stale jiffies update in tick_nohz_restart()
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> Cc: stable@vger.kernel.org Link: http://lkml.kernel.org/r/1332875377-23014-1-git-send-email-ncardwell@google.com Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
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@ -534,9 +534,9 @@ static void tick_nohz_restart(struct tick_sched *ts, ktime_t now)
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hrtimer_get_expires(&ts->sched_timer), 0))
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break;
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}
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/* Update jiffies and reread time */
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tick_do_update_jiffies64(now);
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/* Reread time and update jiffies */
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now = ktime_get();
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tick_do_update_jiffies64(now);
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}
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}
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