On Mon, Oct 07, 2019 at 08:27:38AM +0200, Hannes Reinecke wrote:
> On 10/6/19 4:45 AM, Ming Lei wrote:
> > When all CPUs in one hctx are offline, we shouldn't run this hw queue
> > for completing request any more.
> >
> > So steal bios from the request, and resubmit them, and finally free
> > the request in blk_mq_hctx_notify_dead().
> >
> > Cc: Bart Van Assche <bvanassche@xxxxxxx>
> > Cc: Hannes Reinecke <hare@xxxxxxxx>
> > Cc: Christoph Hellwig <hch@xxxxxx>
> > Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> > Cc: Keith Busch <keith.busch@xxxxxxxxx>
> > Signed-off-by: Ming Lei <ming.lei@xxxxxxxxxx>
> > ---
> > block/blk-mq.c | 48 +++++++++++++++++++++++++++++++++++++++++-------
> > 1 file changed, 41 insertions(+), 7 deletions(-)
> >
> > diff --git a/block/blk-mq.c b/block/blk-mq.c
> > index d991c122abf2..0b35fdbd1f17 100644
> > --- a/block/blk-mq.c
> > +++ b/block/blk-mq.c
> > @@ -2280,10 +2280,30 @@ static int blk_mq_hctx_notify_online(unsigned int cpu, struct hlist_node *node)
> > return 0;
> > }
> >
> > +static void blk_mq_resubmit_io(struct request *rq)
> > +{
> > + struct bio_list list;
> > + struct bio *bio;
> > +
> > + bio_list_init(&list);
> > + blk_steal_bios(&list, rq);
> > +
> > + while (true) {
> > + bio = bio_list_pop(&list);
> > + if (!bio)
> > + break;
> > +
> > + generic_make_request(bio);
> > + }
> > +
> > + blk_mq_cleanup_rq(rq);
> > + blk_mq_end_request(rq, 0);
> > +}
> > +
> Hmm. Not sure if this is a good idea.
> Shouldn't we call 'blk_mq_end_request()' before calling
> generic_make_request()?
> otherwise the cloned request might be completed before original one,
> which looks a bit dodgy to me; and might lead to quite a recursion if we
> have several dead cpus to content with ...
Good catch, we should have freed the old empty request before calling
generic_make_request(), will fix it in V3.
Thanks,
Ming
