From: "Srivatsa S. Bhat" <srivatsa.bhat@linux.vnet.ibm.com>
To: Jiri Kosina <jkosina@suse.cz>
Cc: "Paul E. McKenney" <paul.mckenney@linaro.org>,
Josh Triplett <josh@joshtriplett.org>,
linux-kernel@vger.kernel.org,
"Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Subject: Re: Lockdep complains about commit 1331e7a1bb ("rcu: Remove _rcu_barrier() dependency on __stop_machine()")
Date: Wed, 03 Oct 2012 09:05:31 +0530 [thread overview]
Message-ID: <506BB283.4010800@linux.vnet.ibm.com> (raw)
In-Reply-To: <alpine.LNX.2.00.1210030008590.23544@pobox.suse.cz>
On 10/03/2012 03:47 AM, Jiri Kosina wrote:
> On Wed, 3 Oct 2012, Srivatsa S. Bhat wrote:
>
>> I don't see how this circular locking dependency can occur.. If you are using SLUB,
>> kmem_cache_destroy() releases slab_mutex before it calls rcu_barrier(). If you are
>> using SLAB, kmem_cache_destroy() wraps its whole operation inside get/put_online_cpus(),
>> which means, it cannot run concurrently with a hotplug operation such as cpu_up(). So, I'm
>> rather puzzled at this lockdep splat..
>
> I am using SLAB here.
>
> The scenario I think is very well possible:
>
>
> CPU 0 CPU 1
> kmem_cache_destroy()
What about the get_online_cpus() right here at CPU0 before
calling mutex_lock(slab_mutex)? How can the cpu_up() proceed
on CPU1?? I still don't get it... :(
(kmem_cache_destroy() uses get/put_online_cpus() around acquiring
and releasing slab_mutex).
Regards,
Srivatsa S. Bhat
> mutex_lock(slab_mutex)
> _cpu_up()
> cpu_hotplug_begin()
> mutex_lock(cpu_hotplug.lock)
> rcu_barrier()
> _rcu_barrier()
> get_online_cpus()
> mutex_lock(cpu_hotplug.lock)
> (blocks, CPU 1 has the mutex)
> __cpu_notify()
> mutex_lock(slab_mutex)
>
> Deadlock.
>
> Right?
>
next prev parent reply other threads:[~2012-10-03 3:36 UTC|newest]
Thread overview: 46+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-10-02 16:14 Lockdep complains about commit 1331e7a1bb ("rcu: Remove _rcu_barrier() dependency on __stop_machine()") Jiri Kosina
2012-10-02 17:01 ` Paul E. McKenney
2012-10-02 21:27 ` Jiri Kosina
2012-10-02 21:49 ` Jiri Kosina
2012-10-02 21:58 ` Jiri Kosina
2012-10-02 23:31 ` Paul E. McKenney
2012-10-02 23:48 ` Jiri Kosina
2012-10-03 0:15 ` Paul E. McKenney
2012-10-03 0:45 ` [PATCH] mm, slab: release slab_mutex earlier in kmem_cache_destroy() (was Re: Lockdep complains about commit 1331e7a1bb ("rcu: Remove _rcu_barrier() dependency on __stop_machine()")) Jiri Kosina
2012-10-03 3:41 ` Paul E. McKenney
2012-10-03 3:50 ` Srivatsa S. Bhat
2012-10-03 6:08 ` Srivatsa S. Bhat
2012-10-03 8:21 ` Srivatsa S. Bhat
2012-10-03 9:46 ` [PATCH v2] [RFC] mm, slab: release slab_mutex earlier in kmem_cache_destroy() Jiri Kosina
2012-10-03 12:22 ` Srivatsa S. Bhat
2012-10-03 12:53 ` [PATCH] CPU hotplug, debug: Detect imbalance between get_online_cpus() and put_online_cpus() Srivatsa S. Bhat
2012-10-03 21:13 ` Andrew Morton
2012-10-04 6:16 ` Srivatsa S. Bhat
2012-10-05 3:24 ` Yasuaki Ishimatsu
2012-10-05 5:35 ` Srivatsa S. Bhat
2012-10-03 14:50 ` [PATCH v2] [RFC] mm, slab: release slab_mutex earlier in kmem_cache_destroy() Paul E. McKenney
2012-10-03 14:55 ` Srivatsa S. Bhat
2012-10-03 16:00 ` Paul E. McKenney
2012-10-03 14:17 ` Christoph Lameter
2012-10-03 14:15 ` [PATCH] mm, slab: release slab_mutex earlier in kmem_cache_destroy() (was Re: Lockdep complains about commit 1331e7a1bb ("rcu: Remove _rcu_barrier() dependency on __stop_machine()")) Christoph Lameter
2012-10-03 14:34 ` [PATCH v3] mm, slab: release slab_mutex earlier in kmem_cache_destroy() Jiri Kosina
2012-10-03 15:00 ` Srivatsa S. Bhat
2012-10-03 15:05 ` [PATCH v4] " Jiri Kosina
2012-10-03 15:49 ` Srivatsa S. Bhat
2012-10-03 18:49 ` David Rientjes
2012-10-08 7:26 ` [PATCH] [RESEND] " Jiri Kosina
2012-10-10 6:27 ` Pekka Enberg
2012-10-03 3:59 ` Lockdep complains about commit 1331e7a1bb ("rcu: Remove _rcu_barrier() dependency on __stop_machine()") Srivatsa S. Bhat
2012-10-03 4:07 ` Paul E. McKenney
2012-10-03 4:15 ` Srivatsa S. Bhat
2012-10-02 20:39 ` Srivatsa S. Bhat
2012-10-02 22:17 ` Jiri Kosina
2012-10-03 3:35 ` Srivatsa S. Bhat [this message]
2012-10-03 3:44 ` Paul E. McKenney
2012-10-03 4:04 ` Srivatsa S. Bhat
2012-10-03 7:43 ` Jiri Kosina
2012-10-03 8:11 ` Srivatsa S. Bhat
2012-10-03 8:19 ` Jiri Kosina
2012-10-03 8:30 ` Srivatsa S. Bhat
2012-10-03 9:24 ` Jiri Kosina
2012-10-03 9:58 ` Srivatsa S. Bhat
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