Re: [PATCH 2/9] block: Stop abusing rq->csd.list in blk-softirq

Jan Kara
2014-01-30T15:45:26Z

Hi,

On Thu 30-01-14 13:39:18, Frederic Weisbecker wrote:
> I'm currently working on some cleanups on IPI code too and working on top
> of these patches, just have a few comments:
Great, thanks!

> On Mon, Dec 23, 2013 at 09:39:23PM +0100, Jan Kara wrote:
> > Abusing rq->csd.list for a list of requests to complete is rather ugly.
> > Especially since using queuelist should be safe and much cleaner.
>
> It would be nice to have a few more details that explain why doing so is safe
> wrt a block request lifecycle. At least something that tells why rq->queuelist
> can't be ever used concurrently by the time we send the IPI and we trigger/raise
> the softirq.
Sure. Should I send the patch to you with an updated changelog and added
comment you requested?

> > Signed-off-by: Jan Kara <jack@suse.cz>
> > ---
> > block/blk-softirq.c | 12 ++++++------
> > 1 file changed, 6 insertions(+), 6 deletions(-)
> >
> > diff --git a/block/blk-softirq.c b/block/blk-softirq.c
> > index 57790c1a97eb..7ea5534096d5 100644
> > --- a/block/blk-softirq.c
> > +++ b/block/blk-softirq.c
> > @@ -30,8 +30,8 @@ static void blk_done_softirq(struct softirq_action *h)
> > while (!list_empty(&local_list)) {
> > struct request *rq;
> >
> > - rq = list_entry(local_list.next, struct request, csd.list);
> > - list_del_init(&rq->csd.list);
> > + rq = list_entry(local_list.next, struct request, queuelist);
> > + list_del_init(&rq->queuelist);
> > rq->q->softirq_done_fn(rq);
> > }
> > }
> > @@ -45,9 +45,9 @@ static void trigger_softirq(void *data)
> >
> > local_irq_save(flags);
> > list = this_cpu_ptr(&blk_cpu_done);
> > - list_add_tail(&rq->csd.list, list);
> > + list_add_tail(&rq->queuelist, list);
>
> And given that's an alternate use of rq->queuelist, perhaps add a comment
> to unconfuse people.
Good idea, will do.

Honza

> >
> > - if (list->next == &rq->csd.list)
> > + if (list->next == &rq->queuelist)
> > raise_softirq_irqoff(BLOCK_SOFTIRQ);
> >
> > local_irq_restore(flags);
> > @@ -136,7 +136,7 @@ void __blk_complete_request(struct request *req)
> > struct list_head *list;
> > do_local:
> > list = this_cpu_ptr(&blk_cpu_done);
> > - list_add_tail(&req->csd.list, list);
> > + list_add_tail(&req->queuelist, list);
> >
> > /*
> > * if the list only contains our just added request,
> > @@ -144,7 +144,7 @@ do_local:
> > * entries there, someone already raised the irq but it
> > * hasn't run yet.
> > */
> > - if (list->next == &req->csd.list)
> > + if (list->next == &req->queuelist)
> > raise_softirq_irqoff(BLOCK_SOFTIRQ);
> > } else if (raise_blk_irq(ccpu, req))
> > goto do_local;
> > --
> > 1.8.1.4
> >
--
Jan Kara <jack@suse.cz>
SUSE Labs, CR