From: Jens Axboe Subject: Re: [PATCH 5/8] nowait aio: return on congested block device Date: Thu, 16 Mar 2017 08:33:38 -0600 Message-ID: References: <20170315215107.5628-1-rgoldwyn@suse.de> <20170315215107.5628-6-rgoldwyn@suse.de> Mime-Version: 1.0 Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Cc: jack-IBi9RG/b67k@public.gmane.org, hch-wEGCiKHe2LqWVfeAwA7xHQ@public.gmane.org, linux-block-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-btrfs-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-ext4-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-xfs-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, sagi-NQWnxTmZq1alnMjI0IkVqw@public.gmane.org, avi-VrcmuVmyx1hWk0Htik3J/w@public.gmane.org, linux-api-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, willy-wEGCiKHe2LqWVfeAwA7xHQ@public.gmane.org, Goldwyn Rodrigues To: Goldwyn Rodrigues , linux-fsdevel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org Return-path: In-Reply-To: <20170315215107.5628-6-rgoldwyn-l3A5Bk7waGM@public.gmane.org> Sender: linux-api-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org List-Id: linux-ext4.vger.kernel.org On 03/15/2017 03:51 PM, Goldwyn Rodrigues wrote: > diff --git a/block/blk-core.c b/block/blk-core.c > index 0eeb99e..2e5cba2 100644 > --- a/block/blk-core.c > +++ b/block/blk-core.c > @@ -2014,7 +2019,7 @@ blk_qc_t generic_make_request(struct bio *bio) > do { > struct request_queue *q = bdev_get_queue(bio->bi_bdev); > > - if (likely(blk_queue_enter(q, false) == 0)) { > + if (likely(blk_queue_enter(q, bio_flagged(bio, BIO_NOWAIT)) == 0)) { > struct bio_list hold; > struct bio_list lower, same; > > @@ -2040,7 +2045,10 @@ blk_qc_t generic_make_request(struct bio *bio) > bio_list_merge(&bio_list_on_stack, &same); > bio_list_merge(&bio_list_on_stack, &hold); > } else { > - bio_io_error(bio); > + if (unlikely(bio_flagged(bio, BIO_NOWAIT))) > + bio_wouldblock_error(bio); > + else > + bio_io_error(bio); This doesn't look right. What if the queue is dying, and BIO_NOWAIT just happened to be set? And you're missing wbt_wait() as well as a blocking point. Ditto in blk-mq. > diff --git a/block/blk-mq.c b/block/blk-mq.c > index 159187a..942ce8c 100644 > --- a/block/blk-mq.c > +++ b/block/blk-mq.c > @@ -1518,6 +1518,8 @@ static blk_qc_t blk_mq_make_request(struct request_queue *q, struct bio *bio) > rq = blk_mq_sched_get_request(q, bio, bio->bi_opf, &data); > if (unlikely(!rq)) { > __wbt_done(q->rq_wb, wb_acct); > + if (bio && bio_flagged(bio, BIO_NOWAIT)) > + bio_wouldblock_error(bio); > return BLK_QC_T_NONE; > } > This seems a little fragile now, since not both paths free the bio. -- Jens Axboe