linux-kernel - Re: [PATCH 05/24] elevate write count open()'d files

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Date:	Wed, 19 Sep 2007 18:30:00 +0100
From:	Christoph Hellwig <hch@...radead.org>
To:	Dave Hansen <haveblue@...ibm.com>
Cc:	akpm@...l.org, linux-kernel@...r.kernel.org, hch@...radead.org
Subject: Re: [PATCH 05/24] elevate write count open()'d files

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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