linux-kernel - Re: [patch 2/2] r/o bind mounts: Accept passing a mnt NULL pointer to mnt_drop

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Date:	Fri, 12 Oct 2007 09:10:11 -0700
From:	Dave Hansen <haveblue@...ibm.com>
To:	Jan Blunck <jblunck@...e.de>
Cc:	Linux-Kernel Mailinglist <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...l.org>, Christoph Hellwig <hch@....de>
Subject: Re: [patch 2/2] r/o bind mounts: Accept passing a mnt NULL pointer
	to mnt_drop_write()

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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