linux-kernel - Re: [PATCH] nfs: clear_commit_release incorrectly handle truncated page

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Date:	Tue, 02 Feb 2010 18:17:07 +0300
From:	Dmitry Monakhov <dmonakhov@...nvz.org>
To:	Trond Myklebust <trond.myklebust@....uio.no>
Cc:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	linux-nfs@...r.kernel.org
Subject: Re: [PATCH] nfs: clear_commit_release incorrectly handle truncated page

Trond Myklebust <trond.myklebust@....uio.no> writes:

> On Tue, 2010-02-02 at 13:36 +0300, Dmitry Monakhov wrote: 
>> After page was truncated it lost it's mapping, this result in null
>> pointer dereference on bdi_stat update. In fact we have to decrement
>> bdi_stat even for truncated pages, so let's pass correct mapping in
>> function arguments. Patch against linux-2.6
>> ##TEST_CASE
>> /*
>> Tast case for bug in nfs_clear_request_commit()
>> caused by null pointer dereference in case of truncated page.
>> It takes less than 10 minutes to reproduce the bug.
>
> Something is wrong here. nfs_release_page() returns '0' if the 
> page has an associated write request (i.e. PagePrivate is set), and so
> both invalidate_complete_page() and invalidate_complete_page2() will
> fail.
>
> So what is truncating the page?
truncate_inode_page()
  truncate_complete_page()
    if (page_has_private(page))
       do_invalidatepage()
         ->nfs_invalidate_page()
>
> Trond
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