linux-kernel - Re: Revoking filesystems [was Re: Sysfs attributes racing with unregistration]

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Message-ID: <20120105171157.GA18486@google.com>
Date:	Thu, 5 Jan 2012 09:11:57 -0800
From:	Tejun Heo <tj@...nel.org>
To:	Alan Stern <stern@...land.harvard.edu>
Cc:	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Theodore Ts'o <tytso@....edu>,
	Kernel development list <linux-kernel@...r.kernel.org>,
	Greg Kroah-Hartman <gregkh@...e.de>,
	Kay Sievers <kay.sievers@...y.org>
Subject: Re: Revoking filesystems [was Re: Sysfs attributes racing with
 unregistration]

Hello,

On Thu, Jan 05, 2012 at 11:47:54AM -0500, Alan Stern wrote:
> One problem (which was reported by a user last spring) is that
> del_gendisk() calls device_del() for the disk and bdi_unregister() for
> the disk's backing_dev_info structure.  Now, del_gendisk will leave the
> data structure in memory until the disk's refcount drops to 0, but
> bdi_unregister ignores refcounts and simply erases the bdi->dev
> pointer.  Once this happens, any attempt to call mark_buffer_dirty()
> (for example, by ext4_commit_super) will cause an oops.

Yeah, there were multiple bugs in block device hot-removal path.  I
got some of them fixed recently but didn't get to the bdi one yet.
It's a bug and needs to be fixed regardless of fs revoke support.

Thanks.

-- 
tejun
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