[dm-devel] dm-mq and end_clone_request()

[Hannes Reinecke]

On 08/03/2016 06:55 PM, Bart Van Assche wrote:
> On 08/02/2016 05:40 PM, Mike Snitzer wrote:
>> But I asked you to run the v4.7 kernel patches I
>> pointed to _without_ any of your debug patches.
> 
> I need several patches to fix bugs that are not related to the device
> mapper, e.g. "sched: Avoid that __wait_on_bit_lock() hangs"
> (https://lkml.org/lkml/2016/8/3/289).
> 
Hmm. Can you test with this patch?

diff --git a/drivers/md/dm-mpath.c b/drivers/md/dm-mpath.c
index 7790a70..9daed03 100644
--- a/drivers/md/dm-mpath.c
+++ b/drivers/md/dm-mpath.c
@@ -439,8 +439,7 @@ static int must_push_back(struct multipath *m)
 {
        return (test_bit(MPATHF_QUEUE_IF_NO_PATH, &m->flags) ||
                ((test_bit(MPATHF_QUEUE_IF_NO_PATH, &m->flags) !=
-                 test_bit(MPATHF_SAVED_QUEUE_IF_NO_PATH, &m->flags)) &&
-                dm_noflush_suspending(m->ti)));
+                 test_bit(MPATHF_SAVED_QUEUE_IF_NO_PATH, &m->flags)));
 }

 /*

Reasoning:
The original check for dm_noflush_suspending() was for bio-based
drivers, which needed to queue I/O within the device-mapper core.
So during suspend this I/O would keep a reference to the device-mapper
core and the table couldn't be swapped.
For request-based multipathing, however, the I/O is _never_ held within
the device-mapper core but rather pushed back to the request queue.
IE even for pushback the I/O will never hold a reference to the
device-mapper core, and the tables can be swapped irrespective of the
'dm_noflush_suspend()' setting.

Or that's the idea, at least :-)

Yes Mike, I know, it's not going to work with bio-based multipathing.
But this is just for figuring out where the real issue is.

Cheers,

Hannes
-- 
Dr. Hannes Reinecke		   Teamlead Storage & Networking
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