Re: [PATCH] Fix aic7xxx del_timer_sync() deadlock

[Jens Axboe <axboe@suse.de>]

On Sun, Feb 29 2004, Jeff Garzik wrote:
> Jens Axboe wrote:
> >On Sun, Feb 29 2004, Jeff Garzik wrote:
> >>If you call blk_start_queue() from io completion -- as you should -- 
> >>then it gets called unconditionally, regardless of whether there is IO 
> >>pending or not.  The LLD should only care if it can accept more 
> >>requests.  The opportunity seems to be there, to me...
> >
> >
> >You are still assuming you have io pending when you call
> >blk_stop_queue(). If some condition prevents you from queueing the first
> >request, you call blk_stop_queue() without having anything to start the
> >queue again.
> 
> ok, I got it.  I thought your "io pending" was referring to requests in 
> the request_queue, not requests active in the LLD.
> 
> Still, this is the responsibility of the LLD, right?  For example, 
> before any requests are ever sent to the request_queue, the LLD may 
> choose to call blk_stop_queue() to prevent queueing while it probes or 
> resets the bus.  That would be a case where there is no io pending, for 
> both definitions of the phrase :)  And it would be up to the LLD to call 
> blk_start_queue() again.  Right?

Yeah that's precisely right. So right now it means that the LLD has to
arm some sort of timer to trigger a blk_start_queue(), _or_ call
blk_plug_device() instead of blk_stop_queue() for this particular case.

-- 
Jens Axboe