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:

quoted

On Fri, Jun 27, 2014 at 07:57:38AM -0400, Josh Boyer wrote:

quoted

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 [off-list ref]
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