On 07/25/2016 07:53 PM, Mike Snitzer wrote:
On Thu, Jul 21 2016 at 4:58pm -0400,
Bart Van Assche <bart.vanassche@xxxxxxxxxxx> 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?
Yes, originally multipath was using the device-mapper internal queueing
mechanism, which meant that queued I/O was holding a reference to the
table. So you couldn't change the table while I/O was pending/queued,
and you'd have to unset queue_if_no_path to allow the tables to be swapped.
(Or something. That's the reasoning I gave to myself when seeing that
construct. And I found myself pretty convincing. Not that I've ever
tested that.)
So with commit e809917735ebf ("dm mpath: push back requests instead of
queueing") that obviously isn't true anymore, and I'd love to see that
quirk go.
Cheers,
Hannes
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Dr. Hannes Reinecke Teamlead Storage & Networking
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SUSE LINUX GmbH, Maxfeldstr. 5, 90409 Nürnberg
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