linux-kernel - Re: [PATCH 25/20] sysfs: Only support removing emtpy sysfs directories.

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Message-ID: <Pine.LNX.4.44L0.0905271736460.2669-100000@iolanthe.rowland.org>
Date:	Wed, 27 May 2009 17:38:50 -0400 (EDT)
From:	Alan Stern <stern@...land.harvard.edu>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>
cc:	Kay Sievers <kay.sievers@...y.org>,
	James Bottomley <James.Bottomley@...senpartnership.com>,
	SCSI development list <linux-scsi@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Greg Kroah-Hartman <gregkh@...e.de>,
	Kernel development list <linux-kernel@...r.kernel.org>,
	Tejun Heo <tj@...nel.org>,
	Cornelia Huck <cornelia.huck@...ibm.com>,
	<linux-fsdevel@...r.kernel.org>,
	"Eric W. Biederman" <ebiederm@...stanetworks.com>
Subject: Re: [PATCH 25/20] sysfs: Only support removing emtpy sysfs  directories.

On Wed, 27 May 2009, Eric W. Biederman wrote:

> Alan Stern <stern@...land.harvard.edu> writes:
> 
> >
> > As fas as I know, they can't.  Instead, they can cause the SCSI layer 
> > to unregister a sysfs directory containing a child directory.  :-)
> >
> > Basically, a user program can delay removal of the child (i.e., the
> > target) directory indefinitely, because currently the target isn't
> > unregistered when all its children are removed -- it's unregistered
> > when all its children are _released_.
> 
> Ok.  Is this opens of /dev/sda1 and the like that are being held open by
> userspace that are potentially causing problems?

Yes, plus any other mechanism for preventing a struct device's refcount 
from going to 0.

> I think I have the fix to that...

The fix is to delete the target when its children are deleted, and not
wait until the children are released.

Alan Stern

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