linux-kernel - Re: [patch] mm: mlock: document scary-looking stack expansion mlock chain

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Message-ID: <CANN689FizixMWu7hKMV055=SY_Sg1rmYrB_KAEwOBP1tEOZw+Q@mail.gmail.com>
Date:	Wed, 20 Feb 2013 22:22:58 +0800
From:	Michel Lespinasse <walken@...gle.com>
To:	Ric Mason <ric.masonn@...il.com>
Cc:	Johannes Weiner <hannes@...xchg.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	Hugh Dickins <hughd@...gle.com>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [patch] mm: mlock: document scary-looking stack expansion mlock chain

On Wed, Feb 20, 2013 at 8:51 PM, Ric Mason <ric.masonn@...il.com> wrote:
> On 02/01/2013 02:10 PM, Johannes Weiner wrote:
>>
>> The fact that mlock calls get_user_pages, and get_user_pages might
>> call mlock when expanding a stack looks like a potential recursion.
>
> Why expand stack need call mlock? I can't find it in the codes, could you
> point out to me?

Its hidden in find_expand_vma(). Basically if the existing stack is
already mlocked, any additional stack expansions get mlocked as well.

-- 
Michel "Walken" Lespinasse
A program is never fully debugged until the last user dies.
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