From: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
To: Stephen Boyd <sboyd@kernel.org>,
Thomas Gleixner <tglx@linutronix.de>,
John Stultz <john.stultz@linaro.org>,
linux-kernel@vger.kernel.org
Subject: [PATCH] clocksource: fix double add_timer_on() for watchdog_timer
Date: Fri, 31 Jan 2020 19:08:59 +0300 [thread overview]
Message-ID: <158048693917.4378.13823603769948933793.stgit@buzz> (raw)
I've got couple reports about kernel 4.19 crashes inside QEMU/KVM:
kernel BUG at kernel/time/timer.c:1154!
BUG_ON(timer_pending(timer) || !timer->function) in add_timer_on().
At the same time another cpu got:
general protection fault: 0000 [#1] SMP PTI
of poinson pointer 0xdead000000000200 in:
__hlist_del at include/linux/list.h:681
(inlined by) detach_timer at kernel/time/timer.c:818
(inlined by) expire_timers at kernel/time/timer.c:1355
(inlined by) __run_timers at kernel/time/timer.c:1686
(inlined by) run_timer_softirq at kernel/time/timer.c:1699
Unfortunately kernel logs are badly scrambled, stacktraces are lost.
Printing timer->function before BUG_ON pointed to clocksource_watchdog().
It looks execution of clocksource_watchdog() theoretically could race with
pair clocksource_stop_watchdog() .. clocksource_start_watchdog():
expire_timers()
detach_timer(timer, true);
timer->entry.pprev = NULL;
raw_spin_unlock_irq(&base->lock);
call_timer_fn
clocksource_watchdog()
clocksource_watchdog_kthread() or
clocksource_unbind()
spin_lock_irqsave(&watchdog_lock, flags);
clocksource_stop_watchdog();
del_timer(&watchdog_timer);
watchdog_running = 0;
spin_unlock_irqrestore(&watchdog_lock, flags);
spin_lock_irqsave(&watchdog_lock, flags);
clocksource_start_watchdog();
add_timer_on(&watchdog_timer, ...);
watchdog_running = 1;
spin_unlock_irqrestore(&watchdog_lock, flags);
spin_lock(&watchdog_lock);
add_timer_on(&watchdog_timer, ...);
BUG_ON(timer_pending(timer) || !timer->function);
timer_pending() -> true
BUG()
I.e. inside clocksource_watchdog() watchdog_timer could be already armed.
This patch simply checks timer_pending() before calling add_timer_on().
All operations are synchronized by watchdog_lock.
Signed-off-by: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
---
kernel/time/clocksource.c | 11 +++++++++--
1 file changed, 9 insertions(+), 2 deletions(-)
diff --git a/kernel/time/clocksource.c b/kernel/time/clocksource.c
index fff5f64981c6..428beb69426a 100644
--- a/kernel/time/clocksource.c
+++ b/kernel/time/clocksource.c
@@ -293,8 +293,15 @@ static void clocksource_watchdog(struct timer_list *unused)
next_cpu = cpumask_next(raw_smp_processor_id(), cpu_online_mask);
if (next_cpu >= nr_cpu_ids)
next_cpu = cpumask_first(cpu_online_mask);
- watchdog_timer.expires += WATCHDOG_INTERVAL;
- add_timer_on(&watchdog_timer, next_cpu);
+
+ /*
+ * Arm timer if not already pending: could race with concurrent
+ * pair clocksource_stop_watchdog() clocksource_start_watchdog().
+ */
+ if (!timer_pending(&watchdog_timer)) {
+ watchdog_timer.expires += WATCHDOG_INTERVAL;
+ add_timer_on(&watchdog_timer, next_cpu);
+ }
out:
spin_unlock(&watchdog_lock);
}
next reply other threads:[~2020-01-31 16:09 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-01-31 16:08 Konstantin Khlebnikov [this message]
2020-02-01 11:21 ` [tip: timers/urgent] clocksource: Prevent double add_timer_on() for watchdog_timer tip-bot2 for Konstantin Khlebnikov
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