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Date: Mon, 19 Mar 2001 12:54:51 +0000
From: "Stephen C. Tweedie" <sct@redhat.com>
To: Manfred Spraul <manfred@colorfullife.com>
Cc: Rik van Riel <riel@conectiva.com.br>, linux-kernel@vger.kernel.org,
        "Stephen C. Tweedie" <sct@redhat.com>
Subject: Re: changing mm->mmap_sem  (was: Re: system call for process information?)
Message-ID: <20010319125451.B952@redhat.com>
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In-Reply-To: <001701c0af8e$bd590ac0$5517fea9@local>; from manfred@colorfullife.com on Sun, Mar 18, 2001 at 10:34:38AM +0100
Sender: linux-kernel-owner@vger.kernel.org
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Hi,

On Sun, Mar 18, 2001 at 10:34:38AM +0100, Manfred Spraul wrote:

> > The problem is that mmap_sem seems to be protecting the list
> > of VMAs, so taking _only_ the page_table_lock could let a VMA
> > change under us while a page fault is underway ...
> 
> No, that can't happen.

It can.  Page faults often need to block, so they have to be able to
drop the page_table_lock.  Holding the mmap_sem is all that keeps the
vma intact until the IO is complete.

Cheers,
 Stephen
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