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

Sat Jul 4 04:09:41 EDT 2020

> 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.
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