Subject: Re: [patch 2/2] r/o bind mounts: Accept passing a mnt NULL pointer
	to mnt_drop_write()
From: Dave Hansen <haveblue@us.ibm.com>
To: Jan Blunck <jblunck@suse.de>
Cc: Linux-Kernel Mailinglist <linux-kernel@vger.kernel.org>,
       Andrew Morton <akpm@osdl.org>, Christoph Hellwig <hch@lst.de>
In-Reply-To: <20071012155020.197228145@hasse.suse.de>
References: <20071012155019.747515889@hasse.suse.de>
	 <20071012155020.197228145@hasse.suse.de>
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Date: Fri, 12 Oct 2007 09:10:11 -0700
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On Fri, 2007-10-12 at 17:50 +0200, Jan Blunck wrote:
> In case of somebody opens a file with dentry_open(dentry, NULL, ...) we don't
> want to stumble on the NULL pointer mnt in struct file. 
...
> +++ b/fs/namespace.c
> @@ -253,6 +253,9 @@ void mnt_drop_write(struct vfsmount *mnt
>         int must_check_underflow = 0;
>         struct mnt_writer *cpu_writer;
> 
> +       if (!mnt)
> +               return;

I kinda wish we'd fix these in the callers.  I know we do something
similar to this with mntput(), but I worry a bit that this just
discourages people from using the right interfaces.

Do you have a case where we're actually getting a NULL mount in here?
We had at least one in reiser4 that really revealed some nastiness in
the fs that needed fixing.

-- Dave

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