Re: [PATCH 1/2] block: move queue quiesce into elevator_change()

[Ming Lei <ming.lei@redhat.com>]

On Thu, May 08, 2025 at 07:03:17AM +0200, Christoph Hellwig wrote:
> On Wed, May 07, 2025 at 10:28:24PM +0800, Ming Lei wrote:
> > On Wed, May 07, 2025 at 03:53:49PM +0200, Christoph Hellwig wrote:
> > > On Wed, May 07, 2025 at 08:04:02PM +0800, Ming Lei wrote:
> > > > blk_mq_freeze_queue() can't be called on quiesced queue, otherwise it may
> > > > never return if there is any queued requests.
> > > > 
> > > > Fix it by moving queue quiesce int elevator_change() by adding one flag to
> > > > 'struct elv_change_ctx' for controlling this behavior.
> > > 
> > > Why do we even need to quiesce the queue here, and not anywhere else?
> > 
> > Quiesce is for draining the in-progress critical area, which can't be
> > covered by queue freeze.
> 
> I know.  But why do we care about that for removing a scheduler, but
> not for changing it?

Actually elevator_switch() does quiesce queue, so we can just remove the
queue quiesce around elevator_set_none().


Thanks, 
Ming