Re: [PATCH] blk-mq: remap queues when adding/removing hardware queues

[Omar Sandoval <osandov@osandov.com>]

On Fri, Mar 31, 2017 at 11:59:24AM -0700, Omar Sandoval wrote:
> From: Omar Sandoval <osandov@fb.com>
> 
> blk_mq_update_nr_hw_queues() used to remap hardware queues, which is the
> behavior that drivers expect. However, commit 4e68a011428a changed
> blk_mq_queue_reinit() to not remap queues for the case of CPU
> hotplugging, inadvertently making blk_mq_update_nr_hw_queues() not remap
> queues as well. This breaks, for example, NBD's multi-connection mode,
> leaving the added hardware queues unused. Fix it by making
> blk_mq_queue_reinit() optionally remap queues, which we do when updating
> the number of hardware queues but not when hotplugging.
> 
> Fixes: 4e68a011428a ("blk-mq: don't redistribute hardware queues on a CPU hotplug event")
> Signed-off-by: Omar Sandoval <osandov@fb.com>
> ---
> The only callers of blk_mq_update_nr_hw_queues() are nbd and nbd. I *think*
> nbd_dev_add() also wants this remap behavior.

Uh, I meant nbd and nvme, and nvme_dev_add().