Re: [for-4.16 PATCH v4 3/4] block: allow gendisk's request_queue registration to be deferred

[Mike Snitzer <snitzer@redhat.com>]

On Thu, Jan 11 2018 at  7:37pm -0500,
Bart Van Assche <Bart.VanAssche@wdc.com> wrote:

> On Thu, 2018-01-11 at 15:14 -0500, Mike Snitzer wrote:
> > -void device_add_disk(struct device *parent, struct gendisk *disk)
> > +void device_add_disk_no_queue_reg(struct device *parent, struct gendisk *disk)
> >  {
> >  	dev_t devt;
> >  	int retval;
> > @@ -682,7 +682,6 @@ void device_add_disk(struct device *parent, struct gendisk *disk)
> >  				    exact_match, exact_lock, disk);
> >  	}
> >  	register_disk(parent, disk);
> > -	blk_register_queue(disk);
> >  
> >  	/*
> >  	 * Take an extra ref on queue which will be put on disk_release()
> > @@ -693,6 +692,21 @@ void device_add_disk(struct device *parent, struct gendisk *disk)
> >  	disk_add_events(disk);
> >  	blk_integrity_add(disk);
> >  }
> > +EXPORT_SYMBOL(device_add_disk_no_queue_reg);
> 
> Hello Mike,
> 
> This change can increase the time between the generation of the disk uevent
> and the registration of the request queue sysfs attributes. Can this cause
> any udev rules to fail?

Certainly not for DM (DM has very sophisticated udev rules that wait for
the final dm generated "CHANGE" event before considering a device to be
"ready").

But are you asking about non-DM devices?  I cannot see, what amounts to,
moving blk_register_queue() to the end of device_add_disk() as reason for
concern.  If it were there technically would already be that race.

Mike