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.
Why lockdep produced such an incomplete stacktrace still remains
unexplained.
Thanks,
--
Jiri Kosina
SUSE Labs
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