linux-kernel - Re: [PATCH 03/11] locking, rwsem: introduce basis for down_write

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Message-ID: <20160511180345.GA27728@dhcp22.suse.cz>
Date:	Wed, 11 May 2016 20:03:46 +0200
From:	Michal Hocko <mhocko@...nel.org>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>,
	LKML <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>,
	"David S. Miller" <davem@...emloft.net>,
	Tony Luck <tony.luck@...el.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Chris Zankel <chris@...kel.net>,
	Max Filippov <jcmvbkbc@...il.com>,
	Davidlohr Bueso <dave@...olabs.net>,
	Waiman Long <Waiman.Long@....com>
Subject: Re: [PATCH 03/11] locking, rwsem: introduce basis for
 down_write_killable

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