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SubjectRe: INFO: possible circular locking dependency at cleanup_workqueue_thread
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On Tue, 2009-05-19 at 20:51 +0200, Oleg Nesterov wrote:

> > > > Anyway, you can have a deadlock like this:
> > > >
> > > > CPU 3 CPU 2 CPU 1
> > > > suspend/hibernate
> > > > something:
> > > > rtnl_lock() device_pm_lock()
> > > > -> mutex_lock(&dpm_list_mtx)
> > > >
> > > > mutex_lock(&dpm_list_mtx)
> > > >
> > > > linkwatch_work
> > > > -> rtnl_lock()
> > > > disable_nonboot_cpus()
> > >
> > > let's suppose disable_nonboot_cpus() does not take cpu_add_remove_lock,
> > >
> > > > -> flush CPU 3 workqueue
> > >
> > > in this case the deadlock is still here?
> > >
> > > We can't flush because we hold the lock (dpm_list_mtx) which depends
> > > on another lock taken by work->func(), the "classical" bug with flush.
> > >
> > > No?
> >
> > Yeah, it looks like cpu_add_remove_lock doesn't make a difference...
> > It's just lockdep reporting a longer chain that also leads to a
> > deadlock.
>
> So. we should not call cpu_down/disable_nonboot_cpus under device_pm_lock().
>
> At first glance this was changed by
>
> PM: Change hibernation code ordering
> 4aecd6718939eb3c4145b248369b65f7483a8a02
>
> PM: Change suspend code ordering
> 900af0d973856d6feb6fc088c2d0d3fde57707d3
>
> commits. Rafael, could you take a look?

I just arrived at the same conclusion, heh. I can't say I understand
these changes though, the part about calling the platform differently
may make sense, but calling why disable non-boot CPUs at a different
place?

johannes
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