On Wed, Oct 22, 2014 at 10:57:25PM +0200, Jiri Kosina wrote:
> On Wed, 22 Oct 2014, Paul E. McKenney wrote:
>
> > rcu: More on deadlock between CPU hotplug and expedited grace periods
> >
> > Commit dd56af42bd82 (rcu: Eliminate deadlock between CPU hotplug and
> > expedited grace periods) was incomplete. Although it did eliminate
> > deadlocks involving synchronize_sched_expedited()'s acquisition of
> > cpu_hotplug.lock via get_online_cpus(), it did nothing about the similar
> > deadlock involving acquisition of this same lock via put_online_cpus().
> > This deadlock became apparent with testing involving hibernation.
> >
> > This commit therefore changes put_online_cpus() acquisition of this lock
> > to be conditional, and increments a new cpu_hotplug.puts_pending field
> > in case of acquisition failure. Then cpu_hotplug_begin() checks for this
> > new field being non-zero, and applies any changes to cpu_hotplug.refcount.
> >
>
> Yes, this works. FWIW, please feel free to add
>
> Reported-and-tested-by: Jiri Kosina <[email protected]>
>
> once merging it.
Done, and thank you for both the bug report and the testing!
> Why lockdep produced such an incomplete stacktrace still remains
> unexplained.
On that, I must defer to people more familiar with stack frames.
Thanx, Paul
> Thanks,
>
> --
> Jiri Kosina
> SUSE Labs
>
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