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

[孙世龙 sunshilong]

Hi,

Thank you for your help and patience.

>Jul  3 10:23:31 yx kernel: [ 1176.166204] CPU: 0 PID: 1837 Comm:
>rt_cansend Tainted: G           OE     4.19.84-solve-alc-failure #1
>Jul  3 10:23:31 yx kernel: [ 1176.166209] I-pipe domain: Linux
>Jul  3 10:23:31 yx kernel: [ 1176.166218] RIP:
>0010:queued_spin_lock_slowpath+0xd9/0x1a0
...
>  Jul  3 10:23:31 yx kernel: [ 1176.166252] Call Trace:
> Jul  3 10:23:31 yx kernel: [ 1176.166261]  _raw_spin_lock+0x20/0x30
> Jul  3 10:23:31 yx kernel: [ 1176.166270]  can_write+0x6c/0x2c0 [advcan]
> Jul  3 10:23:31 yx kernel: [ 1176.166292]  __vfs_write+0x3a/0x190

One more question, what's the relation between "queued_spin_lock_slowpath"
and "_raw_spin_lock"?

Best Regards.

孙世龙 sunshilong <sunshilong369 at gmail.com> 于2020年7月4日周六 下午5:13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,  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.