FAILED: patch "[PATCH] tick/nohz: Fix possible missing clock reprog after tick soft" failed to apply to 4.9-stable tree

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

 



The patch below does not apply to the 4.9-stable tree.
If someone wants it applied there, or to any other stable or longterm
tree, then please email the backport, including the original git commit
id to <stable@xxxxxxxxxxxxxxx>.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

>From 7bdb59f1ad474bd7161adc8f923cdef10f2638d1 Mon Sep 17 00:00:00 2001
From: Frederic Weisbecker <fweisbec@xxxxxxxxx>
Date: Tue, 7 Feb 2017 17:44:54 +0100
Subject: [PATCH] tick/nohz: Fix possible missing clock reprog after tick soft
 restart

ts->next_tick keeps track of the next tick deadline in order to optimize
clock programmation on irq exit and avoid redundant clock device writes.

Now if ts->next_tick missed an update, we may spuriously miss a clock
reprog later as the nohz code is fooled by an obsolete next_tick value.

This is what happens here on a specific path: when we observe an
expired timer from the nohz update code on irq exit, we perform a soft
tick restart which simply fires the closest possible tick without
actually exiting the nohz mode and restoring a periodic state. But we
forget to update ts->next_tick accordingly.

As a result, after the next tick resulting from such soft tick restart,
the nohz code sees a stale value on ts->next_tick which doesn't match
the clock deadline that just expired. If that obsolete ts->next_tick
value happens to collide with the actual next tick deadline to be
scheduled, we may spuriously bypass the clock reprogramming. In the
worst case, the tick may never fire again.

Fix this with a ts->next_tick reset on soft tick restart.

Signed-off-by: Frederic Weisbecker <fweisbec@xxxxxxxxx>
Reviewed: Wanpeng Li <wanpeng.li@xxxxxxxxxxx>
Acked-by: Rik van Riel <riel@xxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
Link: http://lkml.kernel.org/r/1486485894-29173-1-git-send-email-fweisbec@xxxxxxxxx
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>

diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
index 74e0388cc88d..fc6f740d0277 100644
--- a/kernel/time/tick-sched.c
+++ b/kernel/time/tick-sched.c
@@ -725,6 +725,11 @@ static ktime_t tick_nohz_stop_sched_tick(struct tick_sched *ts,
 		 */
 		if (delta == 0) {
 			tick_nohz_restart(ts, now);
+			/*
+			 * Make sure next tick stop doesn't get fooled by past
+			 * clock deadline
+			 */
+			ts->next_tick = 0;
 			goto out;
 		}
 	}

--
To unsubscribe from this list: send the line "unsubscribe stable" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html



[Index of Archives]     [Linux Kernel]     [Kernel Development Newbies]     [Linux USB Devel]     [Video for Linux]     [Linux Audio Users]     [Yosemite Hiking]     [Linux Kernel]     [Linux SCSI]