[PATCH] Revert "nvme: remove the .stop_ctrl callout"

[Sagi Grimberg]

> We encountered a problem that the disconnect command hangs.
> After analyzing the log and stack, we found that the triggering
> process is as follows:
> CPU0                          CPU1
> 				nvme_rdma_error_recovery_work
>    				  nvme_rdma_teardown_io_queues
> nvme_do_delete_ctrl                 nvme_stop_queues
>    nvme_remove_namespaces
>    --clear ctrl->namespaces
> 				    nvme_start_queues
> 				    --no ns in ctrl->namespaces
>      nvme_ns_remove		    return(because ctrl is deleting)
>        blk_freeze_queue
> 	blk_mq_freeze_queue_wait
>          --wait for ns to unquiesce to clean infligt IO, hang forever
> 
> This problem was not found in older kernels because we will flush
> err work in nvme_stop_ctrl before nvme_remove_namespaces.It does not
> seem to be modified for functional reasons, the patch can be revert
> to solve the problem.
> 
> Revert commit 794a4cb3d2f7 ("nvme: remove the .stop_ctrl callout")

Indeed this analysis is correct.

Reviewed-by: Sagi Grimberg <sagi at grimberg.me>

Couldn't retrieve the discussion that led to this patch
or the submission of it, but it does add a regression.
Perhaps you should have the title reflect that this is a regression so
stable kernels can pick it up.