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

[Christoph Hellwig <hch@lst.de>]

On Wed, Jun 01, 2022 at 03:09:26PM +0800, Ming Lei wrote:
> > Yes, we probably need a blk_mq_quiesce_queue call like in the incremental
> > patch below.  Do you have any good reproducer, though?
> 
> blktests block/027 should cover this.

That did not trigger the problem for me.

> >  	if (q->elevator) {
> > +		blk_mq_quiesce_queue(q);
> > +
> >  		mutex_lock(&q->sysfs_lock);
> >  		elevator_exit(q);
> >  		mutex_unlock(&q->sysfs_lock);
> > +
> > +		blk_mq_unquiesce_queue(q);
> >  	}
> >  
> 
> 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.