linux-kernel - Re: [PATCH for 3.2.34] memcg: do not trigger OOM from add_to_page_cache

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Message-ID: <20130208164056.GG7557@dhcp22.suse.cz>
Date:	Fri, 8 Feb 2013 17:40:56 +0100
From:	Michal Hocko <mhocko@...e.cz>
To:	Greg Thelen <gthelen@...gle.com>
Cc:	azurIt <azurit@...ox.sk>, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org, cgroups mailinglist <cgroups@...r.kernel.org>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Johannes Weiner <hannes@...xchg.org>
Subject: Re: [PATCH for 3.2.34] memcg: do not trigger OOM from
 add_to_page_cache_locked

On Fri 08-02-13 17:29:18, Michal Hocko wrote:
[...]
> OK, I have checked the allocator slow path and you are right even
> GFP_KERNEL will not fail. This can lead to similar deadlocks - e.g.
> OOM killed task blocked on down_write(mmap_sem) while the page fault
> handler holding mmap_sem for reading and allocating a new page without
> any progress.

And now that I think about it some more it sounds like it shouldn't be
possible because allocator would fail because it would see
TIF_MEMDIE (OOM killer kills all threads that share the same mm).
But maybe there are other locks that are dangerous, but I think that the
risk is pretty low.
-- 
Michal Hocko
SUSE Labs
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