Messages in this thread Patch in this message | | | From | "liujian (CE)" <> | Subject | RE: [Question] softlockup in run_timer_softirq | Date | Wed, 15 Feb 2023 08:34:14 +0000 |
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> -----Original Message----- > From: John Stultz [mailto:jstultz@google.com] > Sent: Tuesday, February 14, 2023 4:01 AM > To: liujian (CE) <liujian56@huawei.com> > Cc: tglx@linutronix.de; sboyd@kernel.org; linux-kernel@vger.kernel.org; > peterz@infradead.org; Paul E. McKenney <paulmck@kernel.org> > Subject: Re: [Question] softlockup in run_timer_softirq > > On Fri, Feb 10, 2023 at 1:51 AM liujian (CE) <liujian56@huawei.com> wrote: > > > > During the syz test, we encountered many problems with various timer > > handler functions softlockup. > > > > We analyze __run_timers() and find the following problem. > > > > In the while loop of __run_timers(), because there are too many timers > > or improper timer handler functions, if the processing time of the > > expired timers is always greater than the time wheel's next_expiry, > > the function will loop infinitely. > > > > The following extreme test case can be used to reproduce the problem. > > An extreme test case[1] is constructed to reproduce the problem. > > Thanks for reporting and sending out this data: > > First, any chance you might submit this as a in-kernel-stress test? > Maybe utilizing the kernel/torture.c framework? > Okay, I'll learn this framework and do this thing. > (Though the test may need to occasionally take a break so the system can > eventually catch up) > > > Is this a problem or an unreasonable use? > > > > Can we limit the running time of __run_timers() [2]? > > > > Does anyone have a good idea to solve this problem? > > So your patch reminds me of Peter's softirq_needs_break() logic: > > https://git.kernel.org/pub/scm/linux/kernel/git/peterz/queue.git/log/?h=co > re/softirq > > Maybe it could extend that series for the timer softirq as well? > Thank you. Yes. Base on the patchset and the extended patch for timer [1], the soft lockup problem does not occur.
By the way, I see this is a very old patchset? Will this patchset push the main line? @John @Peter
[1] Author: Liu Jian <liujian56@huawei.com> Date: Tue Feb 14 09:53:46 2023 +0800
softirq, timer: Use softirq_needs_break() In the while loop of __run_timers(), because there are too many timers or improper timer handler functions, if the processing time of the expired timers is always greater than the time wheel's next_expiry, the function will loop infinitely. To prevent this, use the timeout/break logic provided by SoftIRQs.If the running time exceeds the limit, break the loop and an additional TIMER_SOFTIRQ is triggered. Signed-off-by: Liu Jian <liujian56@huawei.com>
diff --git a/kernel/time/timer.c b/kernel/time/timer.c index 63a8ce7177dd..70744a469a39 100644 --- a/kernel/time/timer.c +++ b/kernel/time/timer.c @@ -1992,7 +1992,7 @@ void timer_clear_idle(void) * __run_timers - run all expired timers (if any) on this CPU. * @base: the timer vector to be processed. */ -static inline void __run_timers(struct timer_base *base) +static inline void __run_timers(struct timer_base *base, struct softirq_action *h) { struct hlist_head heads[LVL_DEPTH]; int levels; @@ -2020,6 +2020,12 @@ static inline void __run_timers(struct timer_base *base) while (levels--) expire_timers(base, heads + levels); + + if (softirq_needs_break(h)) { + if (time_after_eq(jiffies, base->next_expiry)) + __raise_softirq_irqoff(TIMER_SOFTIRQ); + break; + } } raw_spin_unlock_irq(&base->lock); timer_base_unlock_expiry(base); @@ -2032,9 +2038,9 @@ static __latent_entropy void run_timer_softirq(struct softirq_action *h) { struct timer_base *base = this_cpu_ptr(&timer_bases[BASE_STD]); - __run_timers(base); + __run_timers(base, h); if (IS_ENABLED(CONFIG_NO_HZ_COMMON)) - __run_timers(this_cpu_ptr(&timer_bases[BASE_DEF])); + __run_timers(this_cpu_ptr(&timer_bases[BASE_DEF]), h); } /* > thanks > -john
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