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.
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.