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

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Message-ID: <20110701170531.GA3693@tassilo.jf.intel.com>
Date:	Fri, 1 Jul 2011 10:05:31 -0700
From:	Andi Kleen <andi@...stfloor.org>
To:	linux-scsi@...r.kernel.org, linux-kernel@...r.kernel.org
Cc:	axboe@...nel.dk, rjw@...k.pl
Subject: Linux 3.0 oopses when pulling a USB CDROM

Hi,

I found I can reliably crash a 3.0 system by pulling the
USB cable of a mounted USB cdrom (or rather a USB device which
has a builtin fake CD-ROM) 

I suspect it's a regression too.

It ends with a NULL pointer reference on a NULL sdev in 
scsi_prep_state_check. 

Here's a somewhat incomplete backtrace (written down by hand)

scsi_prep_state_check
scsi_setup_blk_pc_cmnd
blk_peek_request
...
scsi_request_fn
...
ioctl_internal_command
...
scsi_set_medium_removal
sr_lock_door
cdrom_release
...
umount

I tried adding a 

	if (!sdev) 
		return BLKPREP_KILL;

to scsi_prep_state_check, but that caused a RCU CPU stall 
and a generally unhappy system instead.

The sdev must be still there in scsi_set_medium_removal because it's 
referenced, so it must get lost somewhere in SCSI or in the block layer.

Any ideas how to fix this?

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