Re: dm-mq and end_clone_request()

[Mike Snitzer <snitzer@redhat.com>]

On Thu, Jul 21 2016 at  4:58pm -0400,
Bart Van Assche <bart.vanassche@sandisk.com> wrote:

> On 07/20/2016 11:33 AM, Mike Snitzer wrote:
> >Would be interesting to know the error returned from map_request()'s
> >ti->type->clone_and_map_rq().  Really should just be DM_MAPIO_REQUEUE.
> >But the stack you've provided shows map_request calling
> >dm_complete_request(), which implies dm_kill_unmapped_request() is being
> >called due to ti->type->clone_and_map_rq() returning < 0.
> 
> Hello Mike,
> 
> Apparently certain requests fail with -EIO because DM_DEV_SUSPEND
> ioctls are being submitted to the same multipath target. As you know
> DM_DEV_SUSPEND changes QUEUE_IF_NO_PATH from 1 into 0. A WARN_ON()
> statement that I added in driver dm-mpath statement learned me that
> multipathd is submitting these DM_DEV_SUSPEND ioctls. In the output
> of strace -fp$(pidof multipathd) I found the following:
> 
> [pid 13927] ioctl(5, DM_TABLE_STATUS, 0x7fa1000483f0) = 0
> [pid 13927] write(1, "mpathbe: failed to setup multipa"..., 35) = 35
> [pid 13927] write(1, "dm-0: uev_add_map failed\n", 25) = 25
> [pid 13927] write(1, "uevent trigger error\n", 21) = 21
> [pid 13927] write(1, "sdh: remove path (uevent)\n", 26) = 26
> [pid 13927] ioctl(5, DM_TABLE_LOAD, 0x7fa1000483f0) = 0
> [pid 13927] ioctl(5, DM_DEV_SUSPEND, 0x7fa1000483f0) = 0
> 
> I'm still analyzing these and other messages.

The various ioctls you're seeing is just multipathd responding to the
failures.  Part of reloading a table (with revised path info, etc) is to
suspend and then resume the device that is being updated.

But I'm not actually sure on the historic reasoning of why
queue_if_no_path is disabled (and active setting saved) on suspend.

I'll think about this further but maybe others recall why?