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author | Konstantin Khlebnikov <khlebnikov@yandex-team.ru> | 2020-01-31 19:08:59 +0300 |
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committer | Thomas Gleixner <tglx@linutronix.de> | 2020-02-01 11:07:56 +0100 |
commit | febac332a819f0e764aa4da62757ba21d18c182b (patch) | |
tree | 277cb2119b882eeffc354eebadef3055c3294c57 /kernel/time/clocksource.c | |
parent | fcfd7345209210ab309f4422a308bad3e1fa6b8c (diff) | |
download | linux-febac332a819f0e764aa4da62757ba21d18c182b.tar.gz |
clocksource: Prevent double add_timer_on() for watchdog_timer
Kernel crashes inside QEMU/KVM are observed: 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 the timer->function before the BUG_ON() pointed to clocksource_watchdog(). The execution of clocksource_watchdog() can race with a sequence of 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. Check timer_pending() before calling add_timer_on(). This is sufficient as all operations are synchronized by watchdog_lock. Fixes: 75c5158f70c0 ("timekeeping: Update clocksource with stop_machine") Signed-off-by: Konstantin Khlebnikov <khlebnikov@yandex-team.ru> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Cc: stable@vger.kernel.org Link: https://lore.kernel.org/r/158048693917.4378.13823603769948933793.stgit@buzz
Diffstat (limited to 'kernel/time/clocksource.c')
-rw-r--r-- | kernel/time/clocksource.c | 11 |
1 files 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); } |