[PATCH] nvme-multipath: fix possible hang in live ns resize with ANA access

[Daniel Wagner]

On Wed, Sep 28, 2022 at 04:58:16PM +0300, Sagi Grimberg wrote:
> When we revalidate paths as part of ns size change (as of commit e7d65803e2bb),
> 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 at lightbitslabs.com>
> Fixes: e7d65803e2bb ("nvme-multipath: revalidate paths during rescan")
> Signed-off-by: Sagi Grimberg <sagi at grimberg.me>

Reviewed-by: Daniel Wagner <dwagner at suse.de>