lkml.org 
[lkml]   [2023]   [Jan]   [1]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
From
SubjectRe: [PATCH] torture: Fix hang during kthread shutdown phase
Date


> On Jan 1, 2023, at 8:02 AM, Zhouyi Zhou <zhouzhouyi@gmail.com> wrote:
>
> On Sun, Jan 1, 2023 at 2:16 PM Joel Fernandes (Google)
> <joel@joelfernandes.org> wrote:
>>
>> During shutdown of rcutorture, the shutdown thread in
>> rcu_torture_cleanup() calls torture_cleanup_begin() which sets fullstop
>> to FULLSTOP_RMMOD. This is enough to cause the rcutorture threads for
>> readers and fakewriters to breakout of their main while loop and start
>> shutting down.
>>
>> Once out of their main loop, they then call torture_kthread_stopping()
>> which in turn waits for kthread_stop() to be called, however
>> rcu_torture_cleanup() has not even called kthread_stop() on those
>> threads yet, it does that a bit later. However, before it gets a chance
>> to do so, torture_kthread_stopping() calls
>> schedule_timeout_interruptible(1) in a tight loop. Tracing confirmed
>> this makes the timer softirq constantly execute timer callbacks, while
>> never returning back to the softirq exit path and is essentially "locked
>> up" because of that. If the softirq preempts the shutdown thread,
>> kthread_stop() may never be called.
>>
>> This commit improves the situation dramatically, by increasing timeout
>> passed to schedule_timeout_interruptible() 1/20th of a second. This
>> causes the timer softirq to not lock up a CPU and everything works fine.
>> Testing has shown 100 runs of TREE07 passing reliably, which was not the
>> case before because of RCU stalls.
> On my Dell PowerEdge R720 with two Intel(R) Xeon(R) CPU E5-2660 128G memory:
> 1) before this patch:
> 3 of 80 rounds failed with "rcu: INFO: rcu_sched detected stalls on
> CPUs/tasks" [1]
> 2) after this patch
> all 80 rounds passed
>
> Tested-by: Zhouyi Zhou <zhouzhouyi@gmail.com>
>

Thanks! Glad to see your tests look good now.

- Joel


> Thanks
> Zhouyi
>
> [1] http://154.220.3.115/logs/20230101/console.log
>>
>> Cc: Paul McKenney <paulmck@kernel.org>
>> Cc: Frederic Weisbecker <fweisbec@gmail.com>
>> Cc: Zhouyi Zhou <zhouzhouyi@gmail.com>
>> Cc: <stable@vger.kernel.org> # 6.0.x
>> Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>
>> ---
>> kernel/torture.c | 2 +-
>> 1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/kernel/torture.c b/kernel/torture.c
>> index 29afc62f2bfe..d024f3b7181f 100644
>> --- a/kernel/torture.c
>> +++ b/kernel/torture.c
>> @@ -915,7 +915,7 @@ void torture_kthread_stopping(char *title)
>> VERBOSE_TOROUT_STRING(buf);
>> while (!kthread_should_stop()) {
>> torture_shutdown_absorb(title);
>> - schedule_timeout_uninterruptible(1);
>> + schedule_timeout_uninterruptible(HZ/20);
>> }
>> }
>> EXPORT_SYMBOL_GPL(torture_kthread_stopping);
>> --
>> 2.39.0.314.g84b9a713c41-goog
>>

\
 
 \ /
  Last update: 2023-03-26 23:24    [W:0.087 / U:0.464 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site