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

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Message-ID: <20110703011630.GA15637@one.firstfloor.org>
Date:	Sun, 3 Jul 2011 03:16:30 +0200
From:	Andi Kleen <andi@...stfloor.org>
To:	Alan Stern <stern@...land.harvard.edu>
Cc:	Andi Kleen <andi@...stfloor.org>,
	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

> > if (trace_scsi && dev->type == &scsi_dev_type &&
> >      trace_scsi_dev[0] == 0 || !strcmp(dev_name(dev), trace_scsi_dev))) {
> > 	dev_printk ...
> 
> These extra puts could be coming from deep inside the device-model
> core, where they operate directly on the underlying kobject instead of
> going through put_device().  For example, removal of sysfs symlinks
> could have this effect.

Ok I could move it to kobject with some complications (need a real
back trace then)

> On my system, at least, the scsi_device's refcount dropped to 0 at the 
> right time.  That wasn't the problem.  The NULL pointer occurs because 
> the request_queue is used after the scsi_device has been removed from 
> visibility; among other things, __scsi_remove_device() sets 
> sdev->request_queue->queuedata to NULL.
> 
> As the comment says, this causes the request function to reject all I/O 
> requests -- but not before trying to dereference the NULL pointer!

Your explanation completely contradicts what James wrote earlier.

Maybe it's good if you guys come up with a common avenue of debugging
before I try further.

-Andi

-- 
ak@...ux.intel.com -- Speaking for myself only.
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