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From: Nick Piggin <npiggin@suse.de>
To: Andrew Morton <akpm@osdl.org>
Cc: Hugh Dickins <hugh@veritas.com>,
	Linux Kernel <linux-kernel@vger.kernel.org>,
	Linux Filesystems <linux-fsdevel@vger.kernel.org>,
	Linux Memory Management <linux-mm@kvack.org>
Subject: Re: [patch 0/9] buffered write deadlock fix
Date: Wed, 31 Jan 2007 02:31:58 +0100	[thread overview]
Message-ID: <20070131013157.GA21285@wotan.suse.de> (raw)
In-Reply-To: <20070130152119.e0a18e58.akpm@osdl.org>

On Tue, Jan 30, 2007 at 03:21:19PM -0800, Andrew Morton wrote:
> On Tue, 30 Jan 2007 12:55:58 -0800
> Andrew Morton <akpm@osdl.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.

If you want to go down the path of carrying state around in task_struct,
you can take the mmap_sem and set a flag, then get_user_pages the source
page and lock both source and destination in ascending order, then your
page fault handler checks the flag and skips mmap_sem, and the rest of
your fault path checks both the page locks you're holding.

At which point you arrive at a horrible mess :)


  reply	other threads:[~2007-01-31  1:32 UTC|newest]

Thread overview: 30+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2007-01-29 10:31 Nick Piggin
2007-01-29 10:31 ` [patch 1/9] fs: libfs buffered write leak fix Nick Piggin
2007-02-02 23:52   ` Andrew Morton
2007-02-03  1:33     ` Nick Piggin
2007-02-03  1:58       ` Andrew Morton
2007-02-03  2:09         ` Nick Piggin
2007-02-03  2:19           ` Andrew Morton
2007-02-03  2:28             ` Nick Piggin
2007-02-03 17:49       ` Jörn Engel
2007-02-04  3:55         ` Nick Piggin
2007-01-29 10:31 ` [patch 2/9] mm: revert "generic_file_buffered_write(): handle zero length iovec segments" Nick Piggin
2007-01-29 10:32 ` [patch 3/9] mm: revert "generic_file_buffered_write(): deadlock on vectored write" Nick Piggin
2007-01-29 10:32 ` [patch 4/9] mm: generic_file_buffered_write cleanup Nick Piggin
2007-01-29 10:32 ` [patch 5/9] mm: debug write deadlocks Nick Piggin
2007-01-29 10:32 ` [patch 6/9] mm: be sure to trim blocks Nick Piggin
2007-01-29 10:32 ` [patch 7/9] mm: cleanup pagecache insertion operations Nick Piggin
2007-01-29 10:32 ` [patch 8/9] mm: generic_file_buffered_write iovec cleanup Nick Piggin
2007-01-29 10:33 ` [patch 9/9] mm: fix pagecache write deadlocks Nick Piggin
2007-01-29 11:11   ` Nick Piggin
2007-02-02 23:53   ` Andrew Morton
2007-02-03  1:38     ` Nick Piggin
2007-01-30 20:55 ` [patch 0/9] buffered write deadlock fix Andrew Morton
2007-01-30 23:21   ` Andrew Morton
2007-01-31  1:31     ` Nick Piggin [this message]
2007-01-31  0:32   ` Nick Piggin
2007-02-02 23:52 ` Andrew Morton
2007-02-03  1:22   ` Nick Piggin
2007-02-03  6:43   ` Suparna Bhattacharya
     [not found]   ` <370516630.03363@ustc.edu.cn>
2007-02-03 15:31     ` Fengguang Wu
2007-02-04  8:49 Nick Piggin

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