[dm-devel] dm mpath: Fix a dm_blk_ioctl() deadlock

[Mike Snitzer]

On Tue, Jun 28 2016 at  2:29pm -0400,
Bart Van Assche <bart.vanassche at sandisk.com> wrote:

> On 06/28/2016 08:15 PM, Mike Snitzer wrote:
> > This patch doesn't make sense.
> > 
> > In the context of dm-mpath.c:multipath_prepare_ioctl, *bdev is only
> > valid if r == 0.  But r == -ENOTCONN so how can *bdev be valid?
> 
> Sorry but the dm code is not my area of expertise. How about the patch
> below? Please note that so far only the queue-length path selector has
> been tested.

Can we go back to what it is you've experienced?  is it that you have
'queue_if_no_path' enabled and are issuing ioctls to an mpath device
(while removing underlying paths) you'll experience a live-lock (_not_
deadlock) once no valid paths exist?

If that isn't what you're hitting then I'd like to better understand how
a request_queue that is "dying" isn't able to keep itself up enough to
fail IO issued to it (to allow normal error handling to trap the IO
failure).

Mike