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Message-ID: <1357260005.4930.6.camel@kernel.cn.ibm.com>
Subject: Re: [PATCH] mm: protect against concurrent vma expansion
From: Simon Jeons <simon.jeons@gmail.com>
To: Michel Lespinasse <walken@google.com>
Cc: Andrew Morton <akpm@linux-foundation.org>, linux-mm@kvack.org,
        Rik van Riel <riel@redhat.com>, Hugh Dickins <hughd@google.com>,
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On Wed, 2012-12-19 at 19:01 -0800, Michel Lespinasse wrote:
> Hi Simon,
> 
> On Wed, Dec 19, 2012 at 5:56 PM, Simon Jeons <simon.jeons@gmail.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)

Sorry for my late response. 

Since expand_stack() will modify vma, then why hold a read lock here?

>