linux-kernel - Re: Linux 3.0 oopses when pulling a USB CDROM

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Message-ID: <Pine.LNX.4.44L0.1107031201200.28411-100000@netrider.rowland.org>
Date:	Sun, 3 Jul 2011 12:06:40 -0400 (EDT)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Andi Kleen <andi@...stfloor.org>
cc:	James Bottomley <James.Bottomley@...senPartnership.com>,
	Dave Jones <davej@...hat.com>, <linux-scsi@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>, <axboe@...nel.dk>, <rjw@...k.pl>,
	<linux-usb@...r.kernel.org>
Subject: Re: Linux 3.0 oopses when pulling a USB CDROM

On Sun, 3 Jul 2011, Alan Stern wrote:

> > Your explanation completely contradicts what James wrote earlier.
> 
> Yes, it does.  I'm claiming that James was on a wrong track or looking
> in the wrong direction.

To amplify: James wrote:

> Right, that wouldn't work.  The sdev in question comes from
> request_queue->queuedata.  That only goes to null when the last
> reference to the sdev has been released.  So the root cause is something
> in sd holding a reference to sdev without actually getting an additional
> refcount.

The third sentence is clearly wrong, because queuedata is set to NULL
when sdev is removed from visibility, not when the last reference to it
has been released, i.e., in __scsi_remove_device() rather than
scsi_device_dev_release_usercontext().

Maybe this means the assignment to queuedata should be moved.  I don't 
know; unlike James, I'm not an expert on the details of the SCSI stack.

Alan Stern

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