linux-kernel - Re: virt_blk BUG: sleeping function called from invalid context

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Date:	Sun, 29 Jun 2014 21:32:22 +0200
From:	Christoph Hellwig <hch@....de>
To:	"Michael S. Tsirkin" <mst@...hat.com>
Cc:	Josh Boyer <jwboyer@...oraproject.org>,
	Rusty Russell <rusty@...tcorp.com.au>,
	virtualization@...ts.linux-foundation.org,
	"Linux-Kernel@...r. Kernel. Org" <linux-kernel@...r.kernel.org>,
	Brian Lane <bcl@...hat.com>, Jens Axboe <axboe@...nel.dk>,
	Christoph Hellwig <hch@....de>
Subject: Re: virt_blk BUG: sleeping function called from invalid context

On Sun, Jun 29, 2014 at 11:26:37AM +0300, Michael S. Tsirkin wrote:
> On Fri, Jun 27, 2014 at 07:57:38AM -0400, Josh Boyer wrote:
> > Hi All,
> > 
> > We've had a report[1] of the virt_blk driver causing a lot of spew
> > because it's calling a sleeping function from an invalid context.  The
> > backtrace is below.  This is with kernel v3.16-rc2-69-gd91d66e88ea9.
> 
> Hi Jens, pls see below - it looks like the call to blk_mq_end_io
> from IRQ context is causing the issue.
> IIUC you switched virtio to this from __blk_end_request_all in
> 
> commit 1cf7e9c68fe84248174e998922b39e508375e7c1
>     virtio_blk: blk-mq support
> 
> Is this always safe?
> I note that at least one other driver is doing this:
> drivers/block/mtip32xx/mtip32xx.c

Just like __blk_end_request_all blk_mq_end_io is supposed to be called
from irq context.  The problem is that the MD bio end_io handler is calling
a sleeping function.  Not sure if that's a bug in MD though given the
kernfs symbols in the all trace and the recent churn in that area.

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