linux-kernel - Re: [PATCH] mm: protect against concurrent vma expansion

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Message-ID: <CANN689FoSGMUi0mC6dzXe5tXo-BL_4eFZ1NF-De38x8mNhPXcg@mail.gmail.com>
Date:	Wed, 19 Dec 2012 19:01:30 -0800
From:	Michel Lespinasse <walken@...gle.com>
To:	Simon Jeons <simon.jeons@...il.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
	Rik van Riel <riel@...hat.com>,
	Hugh Dickins <hughd@...gle.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm: protect against concurrent vma expansion

Hi Simon,

On Wed, Dec 19, 2012 at 5:56 PM, Simon Jeons <simon.jeons@...il.com> wrote:
> One question.
>
> I found that mainly callsite of expand_stack() is #PF, but it holds
> mmap_sem each time before call expand_stack(), how can hold a *shared*
> mmap_sem happen?

the #PF handler calls down_read(&mm->mmap_sem) before calling expand_stack.

I think I'm just confusing you with my terminology; shared lock ==
read lock == several readers might hold it at once (I'd say they share
it)

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