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

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Date:	Sun, 29 Jun 2014 23:47:10 +0300
From:	"Michael S. Tsirkin" <mst@...hat.com>
To:	Christoph Hellwig <hch@....de>
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>,
	Tejun Heo <tj@...nel.org>,
	John McCutchan <john@...nmccutchan.com>,
	Robert Love <rlove@...ve.org>,
	Eric Paris <eparis@...isplace.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: Re: virt_blk BUG: sleeping function called from invalid context

On Sun, Jun 29, 2014 at 09:32:22PM +0200, Christoph Hellwig wrote:
> 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.

My understanding is this:

bitmap_endwrite -> calls sysfs_notify_dirent_safe under spinlock
 -> calls kernfs_notify which takes a mutex.

So I am guessing it is this commit:

commit d911d98748018f7c8facc035ba39c30f5cce6f9c
Author: Tejun Heo <tj@...nel.org>
Date:   Wed Apr 9 11:07:31 2014 -0400

    kernfs: make kernfs_notify() trigger inotify events too

Tejun, what do you think?

Josh, Brian, could you try reverting that commit to see if it helps?

-- 
MST
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