How can I investigate the cause of "watchdog: BUG: soft lockup"?

[孙世龙 sunshilong]

Hi, Valdis Klētnieks

Thank you for taking the time to respond to me.
I have a better understanding of this matter.

>> Can I draw the conclusion that continually acquiring the spinlock causes the soft
>> lockup and the CPU has been stuck for 22s?
>> Can I think in this way?

>No.  It's been stuck for 22s *TRYING* and *FAILING* to get the spinlock.

I see. So there is a thread that has held the corresponding spinlock
for more 22s,  and a CPU is sticking(busy acquiring the spinlock) at the
same duration.
Can I think in this way?

Thank you for your attention to this matter.
Best Regards.

Valdis Klētnieks <valdis.kletnieks at vt.edu> 于2020年7月4日周六 下午4:09写道：

孙世龙 sunshilong <sunshilong369 at gmail.com> 于2020年7月4日周六 下午5:04写道：
>
> Hi, Valdis Klētnieks
>
> Thank you for taking the time to respond to me.
> I have a better understanding of this matter.
>
> >> Can I draw the conclusion that continually acquiring the spinlock causes the soft
> >> lockup and the CPU has been stuck for 22s?
> >> Can I think in this way?
>
> >No.  It's been stuck for 22s *TRYING* and *FAILING* to get the spinlock.
>
> I see. So there is a thread that has held the corresponding spinlock
> for more 22s.
> Can I think in this way?
>
> Thank you for your attention to this matter.
> Best Regards.
>
> Valdis Klētnieks <valdis.kletnieks at vt.edu> 于2020年7月4日周六 下午4:09写道：
> >
> >
> > > Can I draw the conclusion that continually acquiring the spinlock causes the soft
> > > lockup and the CPU has been stuck for 22s?
> > > Can I think in this way?
> >
> > No.  It's been stuck for 22s *TRYING* and *FAILING* to get the spinlock.
> >
> > For comparison - spinlocks are usually used when you need a lock, but the
> > code protected by the lock is short (things like adding to a linked list, etc),
> > so it should again become available in milliseconds - things where it would take
> > longer to put this thread to sleep and wake another one up than we expect
> > to be waiting for this lock.