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Date: Fri, 2 Jun 2017 12:59:44 -0700
From: Andrew Morton <akpm@linux-foundation.org>
Subject: Re: [PATCH] mm,page_alloc: Serialize warn_alloc() if schedulable.
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To: Michal Hocko <mhocko@suse.com>
Cc: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>, linux-mm@kvack.org, xiyou.wangcong@gmail.com, dave.hansen@intel.com, hannes@cmpxchg.org, mgorman@suse.de, vbabka@suse.cz

On Fri, 2 Jun 2017 09:18:18 +0200 Michal Hocko <mhocko@suse.com> wrote:

> On Thu 01-06-17 15:10:22, Andrew Morton wrote:
> > On Thu, 1 Jun 2017 15:28:08 +0200 Michal Hocko <mhocko@suse.com> wrote:
> > 
> > > On Thu 01-06-17 22:11:13, Tetsuo Handa wrote:
> > > > Michal Hocko wrote:
> > > > > On Thu 01-06-17 20:43:47, Tetsuo Handa wrote:
> > > > > > Cong Wang has reported a lockup when running LTP memcg_stress test [1].
> > > > >
> > > > > This seems to be on an old and not pristine kernel. Does it happen also
> > > > > on the vanilla up-to-date kernel?
> > > > 
> > > > 4.9 is not an old kernel! It might be close to the kernel version which
> > > > enterprise distributions would choose for their next long term supported
> > > > version.
> > > > 
> > > > And please stop saying "can you reproduce your problem with latest
> > > > linux-next (or at least latest linux)?" Not everybody can use the vanilla
> > > > up-to-date kernel!
> > > 
> > > The changelog mentioned that the source of stalls is not clear so this
> > > might be out-of-tree patches doing something wrong and dump_stack
> > > showing up just because it is called often. This wouldn't be the first
> > > time I have seen something like that. I am not really keen on adding
> > > heavy lifting for something that is not clearly debugged and based on
> > > hand waving and speculations.
> > 
> > I'm thinking we should serialize warn_alloc anyway, to prevent the
> > output from concurrent calls getting all jumbled together?
> 
> dump_stack already serializes concurrent calls.

Sure.  But warn_alloc() doesn't.

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