From mboxrd@z Thu Jan  1 00:00:00 1970
From: Greg KH <greg@kroah.com>
Date: Thu, 19 Jun 2014 04:49:40 +0000
Subject: Re: Kernel BUG() in block/blk-tag.c:89 causing panic.
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To: linux-hotplug@vger.kernel.org

On Thu, Jun 19, 2014 at 12:42:51AM -0400, Saran Neti wrote:
> Hi,
> 
> I have a many identical looking USB drives in two btrfs multi-device
> configurations. I was unplugging and replugging a few devices to
> identify which physical device belonged to which btrfs filesystem.
> Running "btrfs fi show" during this unplugging/replugging business
> produced the BUG() stack trace shown below. "btrfs fi show" wouldn't
> return and neither would "fdisk -l". When I tried to reboot the
> computer, it panicked forcing me to do a hard reset.
> 
> All hard disks are run-of-the-mill Seagate Expansion or Backup Plus
> drives. They all work fine (data and SMART) when kernel
> detects them at the start. I hit the BUG() twice during
> unplugging/replugging them randomly and I think it could've been when
> I swapped USB ports for identical drives (model/version etc.)
> 
> If more lspci/lsusb information if needed, let me know. I should be
> able to reproduce it again and if needed insert printks and debug on
> mainline.
> 
> # uname -a
> Linux godel 3.15.1-1-ARCH #1 SMP PREEMPT Tue Jun 17 09:32:20 CEST 2014
> x86_64 GNU/Linux

This looks like a scsi bug, can you send this to the
linux-scsi@vger.kernel.org mailing list?

thanks,

greg k-h