Date: Wed, 19 Sep 2007 18:30:00 +0100
From: Christoph Hellwig <hch@infradead.org>
To: Dave Hansen <haveblue@us.ibm.com>
Cc: akpm@osdl.org, linux-kernel@vger.kernel.org, hch@infradead.org
Subject: Re: [PATCH 05/24] elevate write count open()'d files
Message-ID: <20070919173000.GE20917@infradead.org>
Mail-Followup-To: Christoph Hellwig <hch@infradead.org>,
	Dave Hansen <haveblue@us.ibm.com>, akpm@osdl.org,
	linux-kernel@vger.kernel.org
References: <20070917182718.70494C9B@kernel> <20070917182724.5402E082@kernel>
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On Mon, Sep 17, 2007 at 11:27:24AM -0700, Dave Hansen wrote:
> 
> This is the first really tricky patch in the series.  It
> elevates the writer count on a mount each time a
> non-special file is opened for write.
> 
> This is not completely apparent in the patch because the
> two if() conditions in may_open() above the
> mnt_want_write() call are, combined, equivalent to
> special_file().
> 
> There is also an elevated count around the vfs_create()
> call in open_namei().  The count needs to be kept elevated
> all the way into the may_open() call.  Otherwise, when the
> write is dropped, a ro->rw transisition could occur.  This
> would lead to having rw access on the newly created file,
> while the vfsmount is ro.  That is bad.
> 
> Some filesystems forego the use of normal vfs calls to create
> struct files.  Make sure that these users elevate the mnt writer
> count because they will get __fput(), and we need to make
> sure they're balanced.

Ok.

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