Re: [PATCH 5/8] nowait aio: return on congested block device
From: Jens Axboe <hidden>
Date: 2017-03-16 14:33:57
Also in:
linux-block, linux-btrfs, linux-ext4, linux-fsdevel, linux-xfs
On 03/15/2017 03:51 PM, Goldwyn Rodrigues wrote:
quoted hunk ↗ jump to hunk
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.
quoted hunk ↗ jump to hunk
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