[PATCH v2] nvme: fix reconnection fail due to reserved tag allocation

[Chaitanya Kulkarni]

On 3/7/24 03:06, brookxu.cn wrote:
> From: Chunguang Xu <chunguang.xu at shopee.com>
>
> We found a issue on production environment while using NVMe
> over RDMA, admin_q reconnect failed forever while remote
> target and network is ok. After dig into it, we found it
> may caused by a ABBA deadlock due to tag allocation. In my
> case, the tag was hold by a keep alive request waiting
> inside admin_q, as we quiesced admin_q while reset ctrl,
> so the request maked as idle and will not process before
> reset success. As fabric_q shares tagset with admin_q,
> while reconnect remote target, we need a tag for connect
> command, but the only one reserved tag was held by keep
> alive command which waiting inside admin_q. As a result,
> we failed to reconnect admin_q forever. In order to fix
> this issue, I think we should keep two reserved tags for
> admin queue.

plz consider rearranged line length, no change in wording to use the
full length :-

We found a issue on production environment while using NVMe over RDMA,
admin_q reconnect failed forever while remote target and network is ok.
After dig into it, we found it may caused by a ABBA deadlock due to tag
allocation. In my case, the tag was hold by a keep alive request
waiting inside admin_q, as we quiesced admin_q while reset ctrl, so the
request maked as idle and will not process before reset success. As
fabric_q shares tagset with admin_q, while reconnect remote target, we
need a tag for connect command, but the only one reserved tag was held
by keep alive command which waiting inside admin_q. As a result, we
failed to reconnect admin_q forever. In order to fix this issue, I think
we should keep two reserved tags for admin queue.

Rest of the patch looks good and follows the discussion on V1.

Reviewed-by: Chaitanya Kulkarni <kch at nvidia.com>

-ck