Re: [PATCH] blk: start bypass mode in blk_unregister_queue

[Tejun Heo <tj@kernel.org>]

On Thu, Apr 04, 2013 at 10:01:14PM +0800, Aaron Lu wrote:
> In blk_register_queue, we will end bypass mode for the queue; but in
> blk_unregister_queue, we didn't start bypass mode for it. This would
> cause the WARN_ON_ONCE(q->bypass_depth < 0) to trigger if the queue gets
> registered, unregistered and then again registered, e.g. unload scsi
> cdrom module driver sr_mod and then reload it will trigger such a
> warning.
> 
> Signed-off-by: Aaron Lu <aaron.lu@intel.com>

Is this something which actually happens?  Why would an unregistered
queue registered again?  Do we even support that?

Starting a bypass mode can be very expensive and some drivers create
and destroy a lot of queues during probing.  We don't want a call to
blk_queue_bypass_start() on every queue creation / destruction cycle.

Thanks.

-- 
tejun