linux-kernel - Re: [PATCH] mm: fix page_lock_anon

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Message-ID: <BANLkTinsq-XJGvRVmBa6kRp0RTj9NqGWtA@mail.gmail.com>
Date:	Sat, 28 May 2011 16:24:42 -0700
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Hugh Dickins <hughd@...gle.com>
Cc:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH] mm: fix page_lock_anon_vma leaving mutex locked

On Sat, May 28, 2011 at 3:02 PM, Hugh Dickins <hughd@...gle.com> wrote:
>
> But I'm replying before I've given it enough thought,
> mainly to let you know that I am back on it now.

So I applied your other two patches as obvious, but not this one.

I'm wondering - wouldn't it be nicer to just re-check (after getting
the anon_vma lock) that page->mapping still matches anon_mapping?

That said, I do agree with the "anon_vma_root" part of your patch. I
just think you mixed up two independent issues with it: the fact that
we may be unlocking a new root, and the precise check used to
determine whether the anon_vma might have changed.

So my gut feeling is that we should do the "anon_vma" root thing
independently as a fix for the "maybe anon_vma->root changed" issue,
and then as a separate patch decide on how to check whether anon_vma
is still valid.

Hmm?

                   Linus
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