From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
To: "Rafael J. Wysocki" <rjw@rjwysocki.net>
Cc: Lan Tianyu <tianyu.lan@intel.com>,
linux-kernel@vger.kernel.org, mingo@kernel.org,
laijs@cn.fujitsu.com, dipankar@in.ibm.com,
akpm@linux-foundation.org, mathieu.desnoyers@efficios.com,
josh@joshtriplett.org, tglx@linutronix.de, peterz@infradead.org,
rostedt@goodmis.org, dhowells@redhat.com, edumazet@google.com,
dvhart@linux.intel.com, fweisbec@gmail.com, oleg@redhat.com,
bobby.prani@gmail.com
Subject: Re: [PATCH RFC tip/core/rcu] Eliminate deadlock between CPU hotplug and expedited grace periods
Date: Thu, 18 Sep 2014 15:57:42 -0700 [thread overview]
Message-ID: <20140918225742.GV4723@linux.vnet.ibm.com> (raw)
In-Reply-To: <2028813.2ZT7cSJ4eY@vostro.rjw.lan>
On Fri, Sep 19, 2014 at 12:55:11AM +0200, Rafael J. Wysocki wrote:
> On Thursday, September 18, 2014 05:38:45 AM Paul E. McKenney wrote:
> > On Thu, Sep 18, 2014 at 03:15:36PM +0800, Lan Tianyu wrote:
> > > On 2014年09月17日 21:10, Paul E. McKenney wrote:
> > > > On Wed, Sep 17, 2014 at 03:11:42PM +0800, Lan Tianyu wrote:
> > > >> 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.
> > > >
> > > > By default, it would go into 3.19. Do you need it earlier?
> > >
> > > IMO, this is a dead lock bug which is hard to reproduce and the patch
> > > should go into v3.17 and stable tree?
> >
> > The problem with pushing for v3.17 is that I would have to rebase
> > that commit to the bottom of my current stack and redo all my testing.
> > If there were any problems, I could not only miss v3.17, but also miss
> > the v3.18 merge window.
> >
> > So, given that the next merge window happens pretty soon, how about
> > v3.18 and the stable tree?
>
> That sounds good to me.
Very good, I have added it to my v3.18 queue.
Thanx, Paul
prev parent reply other threads:[~2014-09-18 22:57 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-08-28 19:47 [PATCH RFC tip/core/rcu] Eliminate deadlock between CPU hotplug and expedited grace periods Paul E. McKenney
2014-08-29 6:54 ` Lan Tianyu
2014-08-29 13:11 ` Paul E. McKenney
2014-09-01 11:20 ` Peter Zijlstra
2014-09-01 16:05 ` Paul E. McKenney
2014-09-01 16:17 ` Peter Zijlstra
2014-09-02 16:36 ` Paul E. McKenney
2014-09-03 11:31 ` Peter Zijlstra
2014-09-03 15:03 ` Paul E. McKenney
2014-09-03 15:28 ` Peter Zijlstra
2014-09-03 16:38 ` Paul E. McKenney
2014-09-17 7:11 ` Lan Tianyu
2014-09-17 13:10 ` Paul E. McKenney
2014-09-18 7:15 ` Lan Tianyu
2014-09-18 12:38 ` Paul E. McKenney
2014-09-18 22:55 ` Rafael J. Wysocki
2014-09-18 22:57 ` Paul E. McKenney [this message]
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