From: Frederic Weisbecker <fweisbec@gmail.com>
To: Thomas Gleixner <tglx@linutronix.de>
Cc: LKML <linux-kernel@vger.kernel.org>,
Frederic Weisbecker <fweisbec@gmail.com>,
Peter Zijlstra <peterz@infradead.org>,
Wanpeng Li <wanpeng.li@hotmail.com>,
stable@vger.kernel.org, Ingo Molnar <mingo@kernel.org>,
Rik van Riel <riel@redhat.com>
Subject: [PATCH] nohz: Fix possible missing clock reprog after tick soft restart
Date: Tue, 7 Feb 2017 17:44:54 +0100
Message-ID: <1486485894-29173-1-git-send-email-fweisbec@gmail.com> (raw)
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.
Lets fix this with a ts->next_tick reset on soft tick restart.
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Wanpeng Li <wanpeng.li@hotmail.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Rik van Riel <riel@redhat.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: stable@vger.kernel.org
---
kernel/time/tick-sched.c | 5 +++++
1 file changed, 5 insertions(+)
diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
index 74e0388..fc6f740 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;
}
}
--
2.7.4
next reply index
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-02-07 16:44 Frederic Weisbecker [this message]
2017-02-07 20:05 ` Rik van Riel
2017-02-08 1:56 ` Wanpeng Li
2017-02-10 8:45 ` [tip:timers/urgent] tick/nohz: " tip-bot for Frederic Weisbecker
2017-02-17 3:22 ` [PATCH] nohz: " kbuild test robot
2017-02-17 5:34 ` kbuild test robot
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=1486485894-29173-1-git-send-email-fweisbec@gmail.com \
--to=fweisbec@gmail.com \
--cc=linux-kernel@vger.kernel.org \
--cc=mingo@kernel.org \
--cc=peterz@infradead.org \
--cc=riel@redhat.com \
--cc=stable@vger.kernel.org \
--cc=tglx@linutronix.de \
--cc=wanpeng.li@hotmail.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
LKML Archive on lore.kernel.org
Archives are clonable:
git clone --mirror https://lore.kernel.org/lkml/0 lkml/git/0.git
git clone --mirror https://lore.kernel.org/lkml/1 lkml/git/1.git
git clone --mirror https://lore.kernel.org/lkml/2 lkml/git/2.git
git clone --mirror https://lore.kernel.org/lkml/3 lkml/git/3.git
git clone --mirror https://lore.kernel.org/lkml/4 lkml/git/4.git
git clone --mirror https://lore.kernel.org/lkml/5 lkml/git/5.git
git clone --mirror https://lore.kernel.org/lkml/6 lkml/git/6.git
git clone --mirror https://lore.kernel.org/lkml/7 lkml/git/7.git
git clone --mirror https://lore.kernel.org/lkml/8 lkml/git/8.git
git clone --mirror https://lore.kernel.org/lkml/9 lkml/git/9.git
# If you have public-inbox 1.1+ installed, you may
# initialize and index your mirror using the following commands:
public-inbox-init -V2 lkml lkml/ https://lore.kernel.org/lkml \
linux-kernel@vger.kernel.org
public-inbox-index lkml
Example config snippet for mirrors
Newsgroup available over NNTP:
nntp://nntp.lore.kernel.org/org.kernel.vger.linux-kernel
AGPL code for this site: git clone https://public-inbox.org/public-inbox.git