> -----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
On Wed, Feb 15, 2023 at 12:34 AM liujian (CE) <liujian56@huawei.com> wrote:
> > 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);
> }
>
> /*
So I wanted to revive this old thread, as Frank Woo mentioned his team
has seen a similar issue as well.
Liujian: I'm curious if you've made any further progress with your
adapted patch ontop of PeterZ's softirq_needs_break patch series?
Might it be worth re-submitting the whole series for consideration upstream?
thanks
-john
On 2023/5/2 11:06, John Stultz wrote:
> On Wed, Feb 15, 2023 at 12:34 AM liujian (CE) <liujian56@huawei.com> wrote:
>>> 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);
>> }
>>
>> /*
>
> So I wanted to revive this old thread, as Frank Woo mentioned his team
> has seen a similar issue as well.
>
> Liujian: I'm curious if you've made any further progress with your
> adapted patch ontop of PeterZ's softirq_needs_break patch series?
>
Hi John,
Only the commit ("softirq, timer: Use softirq_needs_break()") is
added to the patchset of Peter, and no other modification is made.
> Might it be worth re-submitting the whole series for consideration upstream?
>
I agree very much and expect, because we often encounter similar
problems when doing fuzzy tests (especially when the test machine is poor).
> thanks
> -john
On Wed, May 3, 2023 at 6:50 PM liujian (CE) <liujian56@huawei.com> wrote:
> On 2023/5/2 11:06, John Stultz wrote:
> > So I wanted to revive this old thread, as Frank Woo mentioned his team
> > has seen a similar issue as well.
> >
> > Liujian: I'm curious if you've made any further progress with your
> > adapted patch ontop of PeterZ's softirq_needs_break patch series?
> >
> Hi John,
> Only the commit ("softirq, timer: Use softirq_needs_break()") is
> added to the patchset of Peter, and no other modification is made.
> > Might it be worth re-submitting the whole series for consideration upstream?
> >
> I agree very much and expect, because we often encounter similar
> problems when doing fuzzy tests (especially when the test machine is poor).
Ok. Will you submit the series + your patch to the list for review and
consideration then?
Please include Frank and Rhine on CC so they can validate and provide
Tested-by: tags if it works for them as well.
thanks
-john
On 2023/5/4 10:59, John Stultz wrote:
> On Wed, May 3, 2023 at 6:50 PM liujian (CE) <liujian56@huawei.com> wrote:
>> On 2023/5/2 11:06, John Stultz wrote:
>>> So I wanted to revive this old thread, as Frank Woo mentioned his team
>>> has seen a similar issue as well.
>>>
>>> Liujian: I'm curious if you've made any further progress with your
>>> adapted patch ontop of PeterZ's softirq_needs_break patch series?
>>>
>> Hi John,
>> Only the commit ("softirq, timer: Use softirq_needs_break()") is
>> added to the patchset of Peter, and no other modification is made.
>>> Might it be worth re-submitting the whole series for consideration upstream?
>>>
>> I agree very much and expect, because we often encounter similar
>> problems when doing fuzzy tests (especially when the test machine is poor).
>
> Ok. Will you submit the series + your patch to the list for review and
> consideration then?
>
The patch[1] has been sent out. Please help review it. Thank you very much.
[1]
https://lore.kernel.org/lkml/20230505113315.3307723-1-liujian56@huawei.com/
> Please include Frank and Rhine on CC so they can validate and provide
> Tested-by: tags if it works for them as well.
>
> thanks
> -john
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