Re: [PATCH RFC tip/core/rcu] Eliminate deadlock between CPU hotplug and expedited grace periods

[Lan Tianyu <tianyu.lan@intel.com>]

On 2014年08月29日 03:47, Paul E. McKenney wrote:
> Currently, the expedited grace-period primitives do get_online_cpus().
> This greatly simplifies their implementation, but means that calls to
> them holding locks that are acquired by CPU-hotplug notifiers (to say
> nothing of calls to these primitives from CPU-hotplug notifiers) can
> deadlock.  But this is starting to become inconvenient:
> https://lkml.org/lkml/2014/8/5/754
> 
> This commit avoids the deadlock and retains the simplicity by creating
> a try_get_online_cpus(), which returns false if the get_online_cpus()
> reference count could not immediately be incremented.  If a call to
> try_get_online_cpus() returns true, the expedited primitives operate
> as before.  If a call returns false, the expedited primitives fall back
> to normal grace-period operations.  This falling back of course results
> in increased grace-period latency, but only during times when CPU
> hotplug operations are actually in flight.  The effect should therefore
> be negligible during normal operation.
> 
> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
> Cc: Josh Triplett <josh@joshtriplett.org>
> Cc: "Rafael J. Wysocki" <rjw@rjwysocki.net>
> Cc: Lan Tianyu <tianyu.lan@intel.com>

Hi Paul:
	What's the status of the patch? Will you push it? Thanks.

-- 
Best regards
Tianyu Lan