linux-kernel - Re: [linux-usb-devel] 2.6.19-rc5-mm1

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Date:	Thu, 9 Nov 2006 16:58:31 -0500 (EST)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Andrew Morton <akpm@...l.org>,
	Benoit Boissinot <bboissin@...il.com>,
	Mattia Dongili <malattia@...ux.it>
cc:	USB development list <linux-usb-devel@...ts.sourceforge.net>,
	Kernel development list <linux-kernel@...r.kernel.org>,
	SCSI development list <linux-scsi@...r.kernel.org>
Subject: Re: [linux-usb-devel] 2.6.19-rc5-mm1

On Thu, 9 Nov 2006, Mattia Dongili wrote:

> On Thu, Nov 09, 2006 at 11:04:53AM -0800, Andrew Morton wrote:
> > 
> > (added linux-scsi)
> [...]
> > > [27526.232000] EIP: [<e8074e26>]
> > > scsi_device_dev_release_usercontext+0x36/0x100 [scsi_mod] SS:ESP
> > > 0068:dfdb1e3c
> > > 
> > > full dmesg attached, I can test patches and provide any useful
> > > information if needed (just not now because the dock is at work).
> > 
> > You're the second or third person to report this (to no effect, btw). 
> 
> oh, great. I was going to report the same (had with usb key unplug).
> Linux version 2.6.19-rc5-mm1-1 (mattia@...amune) (gcc version 4.1.2 20060901 (prerelease) (Debian 4.1.1-13)) #4 SMP Wed Nov 8 22:46:11 CET 2006

I don't know exactly where the problem lies, but I have narrowed it down.

In drivers/scsi/sd.c:sd_probe(), the call to add_disk() increases the 
device's refcount by 1.  However in sd_remove(), the call to del_gendisk() 
decreases the device's refcount by 2.  Consequently the structure is 
deallocated too early, causing the oops.

Somebody who knows more than I do about add_disk() and del_gendisk() will 
have to figure what's going wrong.

Alan Stern

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