From: Ingo Molnar <mingo@kernel.org>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: linux-kernel@vger.kernel.org,
Thomas Gleixner <tglx@linutronix.de>,
Peter Zijlstra <a.p.zijlstra@chello.nl>,
Andrew Morton <akpm@linux-foundation.org>
Subject: [GIT PULL] timer fix
Date: Thu, 3 Oct 2019 00:06:07 +0200 [thread overview]
Message-ID: <20191002220607.GA50607@gmail.com> (raw)
Linus,
Please pull the latest timers-urgent-for-linus git tree from:
git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git timers-urgent-for-linus
# HEAD: b9023b91dd020ad7e093baa5122b6968c48cc9e0 tick: broadcast-hrtimer: Fix a race in bc_set_next
Fix a broadcast-timer handling race that can result in spuriously and
indefinitely delayed hrtimers and even RCU stalls if the system is
otherwise quiet.
Thanks,
Ingo
------------------>
Balasubramani Vivekanandan (1):
tick: broadcast-hrtimer: Fix a race in bc_set_next
kernel/time/tick-broadcast-hrtimer.c | 62 +++++++++++++++++-------------------
1 file changed, 29 insertions(+), 33 deletions(-)
diff --git a/kernel/time/tick-broadcast-hrtimer.c b/kernel/time/tick-broadcast-hrtimer.c
index c1f5bb590b5e..b5a65e212df2 100644
--- a/kernel/time/tick-broadcast-hrtimer.c
+++ b/kernel/time/tick-broadcast-hrtimer.c
@@ -42,39 +42,39 @@ static int bc_shutdown(struct clock_event_device *evt)
*/
static int bc_set_next(ktime_t expires, struct clock_event_device *bc)
{
- int bc_moved;
/*
- * We try to cancel the timer first. If the callback is on
- * flight on some other cpu then we let it handle it. If we
- * were able to cancel the timer nothing can rearm it as we
- * own broadcast_lock.
+ * This is called either from enter/exit idle code or from the
+ * broadcast handler. In all cases tick_broadcast_lock is held.
*
- * However we can also be called from the event handler of
- * ce_broadcast_hrtimer itself when it expires. We cannot
- * restart the timer because we are in the callback, but we
- * can set the expiry time and let the callback return
- * HRTIMER_RESTART.
+ * hrtimer_cancel() cannot be called here neither from the
+ * broadcast handler nor from the enter/exit idle code. The idle
+ * code can run into the problem described in bc_shutdown() and the
+ * broadcast handler cannot wait for itself to complete for obvious
+ * reasons.
*
- * Since we are in the idle loop at this point and because
- * hrtimer_{start/cancel} functions call into tracing,
- * calls to these functions must be bound within RCU_NONIDLE.
+ * Each caller tries to arm the hrtimer on its own CPU, but if the
+ * hrtimer callbback function is currently running, then
+ * hrtimer_start() cannot move it and the timer stays on the CPU on
+ * which it is assigned at the moment.
+ *
+ * As this can be called from idle code, the hrtimer_start()
+ * invocation has to be wrapped with RCU_NONIDLE() as
+ * hrtimer_start() can call into tracing.
*/
- RCU_NONIDLE(
- {
- bc_moved = hrtimer_try_to_cancel(&bctimer) >= 0;
- if (bc_moved) {
- hrtimer_start(&bctimer, expires,
- HRTIMER_MODE_ABS_PINNED_HARD);
- }
- }
- );
-
- if (bc_moved) {
- /* Bind the "device" to the cpu */
- bc->bound_on = smp_processor_id();
- } else if (bc->bound_on == smp_processor_id()) {
- hrtimer_set_expires(&bctimer, expires);
- }
+ RCU_NONIDLE( {
+ hrtimer_start(&bctimer, expires, HRTIMER_MODE_ABS_PINNED_HARD);
+ /*
+ * The core tick broadcast mode expects bc->bound_on to be set
+ * correctly to prevent a CPU which has the broadcast hrtimer
+ * armed from going deep idle.
+ *
+ * As tick_broadcast_lock is held, nothing can change the cpu
+ * base which was just established in hrtimer_start() above. So
+ * the below access is safe even without holding the hrtimer
+ * base lock.
+ */
+ bc->bound_on = bctimer.base->cpu_base->cpu;
+ } );
return 0;
}
@@ -100,10 +100,6 @@ static enum hrtimer_restart bc_handler(struct hrtimer *t)
{
ce_broadcast_hrtimer.event_handler(&ce_broadcast_hrtimer);
- if (clockevent_state_oneshot(&ce_broadcast_hrtimer))
- if (ce_broadcast_hrtimer.next_event != KTIME_MAX)
- return HRTIMER_RESTART;
-
return HRTIMER_NORESTART;
}
next reply other threads:[~2019-10-02 22:06 UTC|newest]
Thread overview: 59+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-10-02 22:06 Ingo Molnar [this message]
2019-10-02 23:00 ` [GIT PULL] timer fix pr-tracker-bot
-- strict thread matches above, loose matches on Subject: below --
2024-05-10 11:12 Ingo Molnar
2024-05-10 17:29 ` pr-tracker-bot
2020-06-28 18:39 Ingo Molnar
2020-06-28 22:05 ` pr-tracker-bot
2020-04-25 10:16 Ingo Molnar
2020-04-25 19:30 ` pr-tracker-bot
2019-11-16 21:38 Ingo Molnar
2019-11-17 0:35 ` pr-tracker-bot
2019-09-26 20:18 Ingo Molnar
2019-09-26 23:00 ` pr-tracker-bot
2019-04-12 13:09 Ingo Molnar
2019-04-13 4:05 ` pr-tracker-bot
2018-12-21 12:34 Ingo Molnar
2018-12-21 19:30 ` pr-tracker-bot
2018-12-23 19:29 ` Heiko Carstens
2019-01-17 9:51 ` Ingo Molnar
2019-01-17 15:58 ` Heiko Carstens
2019-01-17 16:57 ` Thomas Gleixner
2018-03-25 9:00 Ingo Molnar
2017-09-24 11:25 Ingo Molnar
2017-08-26 7:17 Ingo Molnar
2017-07-21 10:21 Ingo Molnar
2017-05-12 7:35 Ingo Molnar
2017-01-18 9:37 Ingo Molnar
2016-12-23 22:53 Ingo Molnar
2016-10-18 11:18 Ingo Molnar
2016-07-13 12:58 Ingo Molnar
2016-04-23 11:34 Ingo Molnar
2015-08-14 7:13 Ingo Molnar
2015-07-18 3:06 Ingo Molnar
2015-02-06 18:38 Ingo Molnar
2014-03-29 18:44 Ingo Molnar
2014-01-15 18:27 Ingo Molnar
2013-10-26 12:27 Ingo Molnar
2013-09-18 16:22 Ingo Molnar
2011-10-17 1:39 Linux 3.1-rc9 Linus Torvalds
2011-10-17 10:34 ` Peter Zijlstra
2011-10-17 14:57 ` Linus Torvalds
2011-10-17 17:54 ` Peter Zijlstra
2011-10-17 18:31 ` Linus Torvalds
2011-10-17 19:23 ` Peter Zijlstra
2011-10-17 21:00 ` Thomas Gleixner
2011-10-18 8:39 ` Thomas Gleixner
2011-10-18 9:05 ` Peter Zijlstra
2011-10-18 14:59 ` Linus Torvalds
2011-10-18 18:14 ` [GIT PULL] timer fix Ingo Molnar
2011-04-29 18:11 Ingo Molnar
2011-02-28 17:39 Ingo Molnar
2011-02-15 17:06 Ingo Molnar
2010-01-31 17:26 Ingo Molnar
2009-10-02 12:38 Ingo Molnar
2009-09-26 12:27 Ingo Molnar
2009-08-09 16:09 Ingo Molnar
2009-08-04 19:04 Ingo Molnar
2009-06-20 16:55 Ingo Molnar
2009-02-17 16:38 [git pull] " Ingo Molnar
2009-02-04 19:25 Ingo Molnar
2009-02-04 22:11 ` Linus Torvalds
2009-02-04 22:16 ` Linus Torvalds
2009-02-04 22:25 ` Ingo Molnar
2009-02-04 22:58 ` Ingo Molnar
2009-02-04 23:13 ` H. Peter Anvin
2009-02-05 0:04 ` Ingo Molnar
2009-02-05 7:51 ` Kirill Korotaev
2009-02-05 9:58 ` Pavel Emelyanov
2009-02-05 14:30 ` Ingo Molnar
2009-02-05 16:04 ` Ray Lee
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