When we revalidate paths as part of ns size change (as of commit
e7d65803), it is possible that during the path revalidation, the
only paths that is IO capable (i.e. optimized/non-optimized) are the
ones that ns resize was not yet informed to the host, which will cause
inflight requests to be requeued (as we have available paths but none
are IO capable). These requests on the requeue list are waiting for
someone to resubmit them at some point.

The IO capable paths will eventually notify the ns resize change to the
host, but there is nothing that will kick the requeue list to resubmit
the queued requests.

Fix this by always kicking the requeue list, and if no IO capable path
exists, these requests will be queued again.

A typical log that indicates that IOs are requeued:
--
nvme nvme1: creating 4 I/O queues.
nvme nvme1: new ctrl: "testnqn1"
nvme nvme2: creating 4 I/O queues.
nvme nvme2: mapped 4/0/0 default/read/poll queues.
nvme nvme2: new ctrl: NQN "testnqn1", addr 127.0.0.1:8009
nvme nvme1: rescanning namespaces.
nvme1n1: detected capacity change from 2097152 to 4194304
block nvme1n1: no usable path - requeuing I/O
block nvme1n1: no usable path - requeuing I/O
block nvme1n1: no usable path - requeuing I/O
block nvme1n1: no usable path - requeuing I/O
block nvme1n1: no usable path - requeuing I/O
block nvme1n1: no usable path - requeuing I/O
block nvme1n1: no usable path - requeuing I/O
block nvme1n1: no usable path - requeuing I/O
block nvme1n1: no usable path - requeuing I/O
block nvme1n1: no usable path - requeuing I/O
nvme nvme2: rescanning namespaces.
--
Reported-by: Yogev Cohen <yogev@lightbitslabs.com>
Fixes: e7d65803 ("nvme-multipath: revalidate paths during rescan")
Signed-off-by: Sagi Grimberg <sagi@grimberg.me>
Cc: <stable@vger.kernel.org> # v5.15+
Signed-off-by: Christoph Hellwig <hch@lst.de>