Messages in this thread | | | Date | Wed, 24 Jul 2002 15:25:29 +0200 | From | Jens Axboe <> | Subject | Re: please DON'T run 2.5.27 with IDE! |
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On Wed, Jul 24 2002, Marcin Dalecki wrote: > Jens Axboe wrote: > > >>>>2.5.27:drivers/block/ll_rw_blk.c > >>>>void blk_start_queue(request_queue_t *q) > >>>>{ > >>>> if (test_and_clear_bit(QUEUE_FLAG_STOPPED, &q->queue_flags)) { > >>>> unsigned long flags; > >>>> > >>>> spin_lock_irqsave(q->queue_lock, flags); > >>>> if (!elv_queue_empty(q)) > >>>> q->request_fn(q); > >>>> spin_unlock_irqrestore(q->queue_lock, flags); > >>>> } > >>>>} > > >There were buggy versions at one point, however they may not have made it > >into a full release. In that case it was just bk version of 2.5.19-pre > >effectively. I forget the details :-) > > Naj - it's far more trivial I just looked at wrong tree at hand... > But anyway. What happens if somone does set QUEUE_FLAG_STOPPED > between the test_and_claer_bit and taking the spin_lock? Setting > the QUEUE_FLAG_STOPPED isn't maintaining the spin_lock protection!
It doesn't matter. If QUEUE_FLAG_STOPPED was set when entering blk_start_queue(), it will call into the request_fn. If blk_stop_queue() is called between clearing QUEUE_FLAG_STOPPED in blk_start_queue() and grabbing the spin_lock, the worst that can happen is a spurios extra request_fn call.
> My goal is to make sure that the QUEUE_FLAG_STOPPED has a valid value > *inside* the q->request_fn call.
So you want the queue_lock to protect the flags as well... I don't really see the point of this.
-- Jens Axboe
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