This is a note to let you know that I've just added the patch titled
nohz: Fix stale jiffies update in tick_nohz_restart()
to the 3.3-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
nohz-fix-stale-jiffies-update-in-tick_nohz_restart.patch
and it can be found in the queue-3.3 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <[email protected]> know about it.
>From 6f103929f8979d2638e58d7f7fda0beefcb8ee7e Mon Sep 17 00:00:00 2001
From: Neal Cardwell <[email protected]>
Date: Tue, 27 Mar 2012 15:09:37 -0400
Subject: nohz: Fix stale jiffies update in tick_nohz_restart()
From: Neal Cardwell <[email protected]>
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 <[email protected]>
Cc: Ben Segall <[email protected]>
Cc: Ingo Molnar <[email protected]>
Link:
http://lkml.kernel.org/r/[email protected]
Signed-off-by: Thomas Gleixner <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>
---
kernel/time/tick-sched.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
--- a/kernel/time/tick-sched.c
+++ b/kernel/time/tick-sched.c
@@ -538,9 +538,9 @@ static void tick_nohz_restart(struct tic
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);
}
}
Patches currently in stable-queue which might be from [email protected] are
queue-3.3/nohz-fix-stale-jiffies-update-in-tick_nohz_restart.patch
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