Re: [PATCH] block: disable the elevator int del_gendisk

[Christoph Hellwig <hch@lst.de>]

On Wed, Jun 01, 2022 at 05:07:53PM +0800, Ming Lei wrote:
> > > I am afraid the above way may slow down disk shutdown a lot, see
> > > the following commit, that is also the reason why I moved it into disk
> > > release handler, when any sync io submission are done.
> > 
> > SCSI devices that are just probed and never had a disk attached will
> > not have q->elevator set and not hit this quiesce at all.
> 
> Yes, but host with hundreds of real LUNs may be shutdown slowly too
> since sd_remove() won't be called in async way.

So maybe teardown will slow down.  But we fix a reproducable bug, and
do get the lifetimes right.  The sched request are enabled in add_disk
(or when a scheduler is enabled if there was none after that) so we
should tear it down in del_gendisk.  The fact that we've been playing
so lose with these lifetime rules in the block layer has been a constant
source of bugs.