linux-kernel - Re: [patch 0/9] buffered write deadlock fix

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Message-Id: <20070130152119.e0a18e58.akpm@osdl.org>
Date:	Tue, 30 Jan 2007 15:21:19 -0800
From:	Andrew Morton <akpm@...l.org>
To:	Nick Piggin <npiggin@...e.de>, Hugh Dickins <hugh@...itas.com>,
	Linux Kernel <linux-kernel@...r.kernel.org>,
	Linux Filesystems <linux-fsdevel@...r.kernel.org>,
	Linux Memory Management <linux-mm@...ck.org>
Subject: Re: [patch 0/9] buffered write deadlock fix

On Tue, 30 Jan 2007 12:55:58 -0800
Andrew Morton <akpm@...l.org> wrote:

> y'know, four or five years back I fixed this bug by doing
> 
> 	current->locked_page = page;
> 
> in the write() code, and then teaching the pagefault code to avoid locking
> the same page.  Patch below.
> 
> But then evil mean Hugh pointed out that the patch is still vulnerable to
> ab/ba deadlocking so I dropped it.

And he was right, of course.  Task A holds file a's i_mutex and takes a
fault against file b's page.  Task B holds file b's i_mutex and takes a
fault against file a's page.  Drat.

I wonder if there's a sane way of preventing that.
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