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

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Message-ID: <5419342E.60602@intel.com>
Date:	Wed, 17 Sep 2014 15:11:42 +0800
From:	Lan Tianyu <tianyu.lan@...el.com>
To:	paulmck@...ux.vnet.ibm.com, linux-kernel@...r.kernel.org
CC:	mingo@...nel.org, laijs@...fujitsu.com, dipankar@...ibm.com,
	akpm@...ux-foundation.org, mathieu.desnoyers@...icios.com,
	josh@...htriplett.org, tglx@...utronix.de, peterz@...radead.org,
	rostedt@...dmis.org, dhowells@...hat.com, edumazet@...gle.com,
	dvhart@...ux.intel.com, fweisbec@...il.com, oleg@...hat.com,
	bobby.prani@...il.com, "Rafael J. Wysocki" <rjw@...ysocki.net>
Subject: Re: [PATCH RFC tip/core/rcu] Eliminate deadlock between CPU hotplug
 and expedited grace periods

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@...ux.vnet.ibm.com>
> Cc: Josh Triplett <josh@...htriplett.org>
> Cc: "Rafael J. Wysocki" <rjw@...ysocki.net>
> Cc: Lan Tianyu <tianyu.lan@...el.com>

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

-- 
Best regards
Tianyu Lan
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