linux-kernel - Re: Lockdep splat involving all_q

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Message-Id: <20170511031354.GB3956@linux.vnet.ibm.com>
Date:   Wed, 10 May 2017 20:13:54 -0700
From:   "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:     Jens Axboe <axboe@...nel.dk>
Cc:     peterz@...radead.org, linux-kernel@...r.kernel.org,
        rostedt@...dmis.org, tglx@...utronix.de
Subject: Re: Lockdep splat involving all_q_mutex

On Wed, May 10, 2017 at 08:55:54PM -0600, Jens Axboe wrote:
> On 05/10/2017 04:34 PM, Paul E. McKenney wrote:
> > Hello!
> > 
> > I got the lockdep splat shown below during some rcutorture testing (which
> > does CPU hotplug operations) on mainline at commit dc9edaab90de ("Merge
> > tag 'acpi-extra-4.12-rc1' of git://git.kernel.org/.../rafael/linux-pm").
> > My kneejerk reaction was just to reverse the "mutex_lock(&all_q_mutex);"
> > and "get_online_cpus();" in blk_mq_init_allocated_queue(), but then
> > I noticed that commit eabe06595d62 ("block/mq: Cure cpu hotplug lock
> > inversion") just got done moving these two statements in the other
> > direction.
> 
> The problem is that that patch got merged too early, as it only
> fixes a lockdep splat with the cpu hotplug rework. Fix is coming Linus'
> way, it's in my for-linus tree.

Thank you for the update, looking forward to the fix.

							Thanx, Paul