linux-kernel - Re: [PATCH] Introduce freeze_super and thaw

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Message-ID: <20100323234719.GM30031@ZenIV.linux.org.uk>
Date:	Tue, 23 Mar 2010 23:47:19 +0000
From:	Al Viro <viro@...IV.linux.org.uk>
To:	Nigel Cunningham <ncunningham@...a.org.au>
Cc:	Josef Bacik <josef@...hat.com>, linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org, chris.mason@...cle.com, hch@....de
Subject: Re: [PATCH] Introduce freeze_super and thaw_super for the fsfreeze
 ioctl

On Tue, Mar 23, 2010 at 11:18:03PM +0000, Al Viro wrote:
> [snip the horror]
> 
> 	a) traversing superblock list without any locking whatsoever
> 	b) accessing superblock fields <....>
> 	c) <.........................> without making sure that it's not
> going to disappear
> 	d) calling freeze_bdev() without any warranties that its argument
> is not going to be freed under you
> 	e) layering violations all over the place
> etc.

BTW, superblock can be kept alive by an opened file.  umount -l, for example,
will give that.  So it can get freed whenever the last reference to struct
file can go away (AF_UNIX garbage collection, etc.)
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