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Date: Wed, 11 May 2016 20:03:46 +0200
From: Michal Hocko <mhocko@kernel.org>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>,
        LKML <linux-kernel@vger.kernel.org>, Ingo Molnar <mingo@redhat.com>,
        Thomas Gleixner <tglx@linutronix.de>, "H. Peter Anvin" <hpa@zytor.com>,
        "David S. Miller" <davem@davemloft.net>,
        Tony Luck <tony.luck@intel.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Chris Zankel <chris@zankel.net>, Max Filippov <jcmvbkbc@gmail.com>,
        Davidlohr Bueso <dave@stgolabs.net>, Waiman Long <Waiman.Long@hpe.com>
Subject: Re: [PATCH 03/11] locking, rwsem: introduce basis for
 down_write_killable
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On Wed 11-05-16 15:59:38, Michal Hocko wrote:
> On Wed 11-05-16 11:41:28, Peter Zijlstra wrote:
> > On Wed, May 11, 2016 at 11:31:27AM +0200, Michal Hocko wrote:
> > 
> > > Care to cook up a full patch?
> > 
> > compile tested only, if someone could please test it?
> 
> I have tried to run the test case from Tetsuo[1] with a small printk to
> show the interrupted writer case:
> [ 2753.596678] XXX: Writer interrupted. Woken waiters:0
> [ 2998.266978] XXX: Writer interrupted. Woken waiters:0
> 
> which means rwsem_atomic_update(-RWSEM_WAITING_BIAS, sem) path which is
> the problematic case. oom_reaper was always able to succeed so I guess
> the patch works as expected. I will leave the test run for longer to be
> sure.

And just for the reference I am able to reproduce the lockup without the
patch applied and the same test case and a debugging patch

[ 1522.036379] XXX interrupted. list_is_singular:1
[ 1523.040462] oom_reaper: unable to reap pid:3736 (tgid=3736)

I still cannot say I would understand why the pending
RWSEM_WAITING_BIAS matters but I would probably need to look at the code
again with a clean head, __rwsem_wake is quite tricky...
-- 
Michal Hocko
SUSE Labs