Re: [PATCH 4/7] ide: ide_hwgroup_t.rq doesn't need an ide_lock held

[Jens Axboe <jens.axboe@oracle.com>]

On Fri, Oct 10 2008, Elias Oltmanns wrote:
> Jens Axboe <jens.axboe@oracle.com> wrote:
> > On Fri, Oct 10 2008, Elias Oltmanns wrote:
> >> Bartlomiej Zolnierkiewicz <bzolnier@gmail.com> wrote:
> >
> >> > From: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>
> >> > Subject: [PATCH] ide: ide_hwgroup_t.rq doesn't need an ide_lock held
> >> >
> >> > While at it:
> >> > - no need to check for hwgroup presence in ide_dump_opcode()
> >> >
> >> > Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>
> >> > ---
> >> [...]
> >> > Index: b/drivers/ide/ide-io.c
> >> > ===================================================================
> >> > --- a/drivers/ide/ide-io.c
> >> > +++ b/drivers/ide/ide-io.c
> >> [...]
> >> > @@ -274,7 +269,11 @@ static void ide_complete_pm_request (ide
> >> >  		drive->dev_flags &= ~IDE_DFLAG_BLOCKED;
> >> >  		blk_start_queue(drive->queue);
> >> >  	}
> >> > -	HWGROUP(drive)->rq = NULL;
> >> > +	spin_unlock_irqrestore(&ide_lock, flags);
> >> > +
> >> > +	drive->hwif->hwgroup->rq = NULL;
> >> > +
> >> > +	spin_lock_irqsave(&ide_lock, flags);
> >> >  	if (__blk_end_request(rq, 0, 0))
> >> >  		BUG();
> >> >  	spin_unlock_irqrestore(&ide_lock, flags);
> >> 
> >> Is it really an improvement to release the lock here?
> >
> > And more importantly, is it even safe? What serializes ->rq assignments
> > and checks without the ide_lock? Looks fishy.
> 
> Well, I haven't quite made up my mind whether it'll work in all cases,
> but I think the hwgroup->busy flag is supposed to take care of that.

It used to be especially problematic with multi count IO, but my
knowledge and last check on that dates back to pre-2000 I think...

-- 
Jens Axboe