[PATCH 4/7] nonblocking aio: return on congested block device

[Goldwyn Rodrigues <rgoldwyn@xxxxxxx>]

From: Goldwyn Rodrigues <rgoldwyn@xxxxxxxx>

A new flag BIO_NONBLOCKING is introduced to identify bio's
orignating from iocb with IOCB_NONBLOCKING. struct request
are requested using BLK_MQ_REQ_NOWAIT if BIO_NONBLOCKING is set.

Signed-off-by: Goldwyn Rodrigues <rgoldwyn@xxxxxxxx>
---
 block/blk-core.c          | 13 +++++++++++--
 block/blk-mq.c            | 18 ++++++++++++++++--
 fs/direct-io.c            | 11 +++++++++--
 include/linux/blk_types.h |  1 +
 4 files changed, 37 insertions(+), 6 deletions(-)

diff --git a/block/blk-core.c b/block/blk-core.c
index 14d7c07..9767573 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -1257,6 +1257,11 @@ static struct request *get_request(struct request_queue *q, int op,
 	if (!IS_ERR(rq))
 		return rq;
 
+	if (bio_flagged(bio, BIO_NONBLOCKING)) {
+		blk_put_rl(rl);
+		return ERR_PTR(-EAGAIN);
+	}
+
 	if (!gfpflags_allow_blocking(gfp_mask) || unlikely(blk_queue_dying(q))) {
 		blk_put_rl(rl);
 		return rq;
@@ -2035,7 +2040,7 @@ 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_NONBLOCKING)) == 0)) {
 			ret = q->make_request_fn(q, bio);
 
 			blk_queue_exit(q);
@@ -2044,7 +2049,11 @@ blk_qc_t generic_make_request(struct bio *bio)
 		} else {
 			struct bio *bio_next = bio_list_pop(current->bio_list);
 
-			bio_io_error(bio);
+			if (unlikely(bio_flagged(bio, BIO_NONBLOCKING))) {
+				bio->bi_error = -EAGAIN;
+				bio_endio(bio);
+			} else
+				bio_io_error(bio);
 			bio = bio_next;
 		}
 	} while (bio);
diff --git a/block/blk-mq.c b/block/blk-mq.c
index 81caceb..7a7c674 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -1213,6 +1213,8 @@ static struct request *blk_mq_map_request(struct request_queue *q,
 
 	trace_block_getrq(q, bio, op);
 	blk_mq_set_alloc_data(&alloc_data, q, 0, ctx, hctx);
+	if (bio_flagged(bio, BIO_NONBLOCKING))
+		alloc_data.flags |= BLK_MQ_REQ_NOWAIT;
 	rq = __blk_mq_alloc_request(&alloc_data, op, op_flags);
 
 	data->hctx = alloc_data.hctx;
@@ -1286,8 +1288,14 @@ static blk_qc_t blk_mq_make_request(struct request_queue *q, struct bio *bio)
 		return BLK_QC_T_NONE;
 
 	rq = blk_mq_map_request(q, bio, &data);
-	if (unlikely(!rq))
+	if (unlikely(!rq)) {
+		if (bio_flagged(bio, BIO_NONBLOCKING))
+			bio->bi_error = -EAGAIN;
+		else
+			bio->bi_error = -EIO;
+		bio_endio(bio);
 		return BLK_QC_T_NONE;
+	}
 
 	cookie = blk_tag_to_qc_t(rq->tag, data.hctx->queue_num);
 
@@ -1381,8 +1389,14 @@ static blk_qc_t blk_sq_make_request(struct request_queue *q, struct bio *bio)
 		request_count = blk_plug_queued_count(q);
 
 	rq = blk_mq_map_request(q, bio, &data);
-	if (unlikely(!rq))
+	if (unlikely(!rq)) {
+		if (bio_flagged(bio, BIO_NONBLOCKING))
+			bio->bi_error = -EAGAIN;
+		else
+			bio->bi_error = -EIO;
+		bio_endio(bio);
 		return BLK_QC_T_NONE;
+	}
 
 	cookie = blk_tag_to_qc_t(rq->tag, data.hctx->queue_num);
 
diff --git a/fs/direct-io.c b/fs/direct-io.c
index fb9aa16..9997fed 100644
--- a/fs/direct-io.c
+++ b/fs/direct-io.c
@@ -386,6 +386,9 @@ dio_bio_alloc(struct dio *dio, struct dio_submit *sdio,
 	else
 		bio->bi_end_io = dio_bio_end_io;
 
+	if (dio->iocb->ki_flags & IOCB_NONBLOCKING)
+		bio_set_flag(bio, BIO_NONBLOCKING);
+
 	sdio->bio = bio;
 	sdio->logical_offset_in_bio = sdio->cur_page_fs_offset;
 }
@@ -480,8 +483,12 @@ static int dio_bio_complete(struct dio *dio, struct bio *bio)
 	unsigned i;
 	int err;
 
-	if (bio->bi_error)
-		dio->io_error = -EIO;
+	if (bio->bi_error) {
+		if (bio_flagged(bio, BIO_NONBLOCKING))
+			dio->io_error = bio->bi_error;
+		else
+			dio->io_error = -EIO;
+	}
 
 	if (dio->is_async && dio->op == REQ_OP_READ && dio->should_dirty) {
 		err = bio->bi_error;
diff --git a/include/linux/blk_types.h b/include/linux/blk_types.h
index cd395ec..94855cf 100644
--- a/include/linux/blk_types.h
+++ b/include/linux/blk_types.h
@@ -119,6 +119,7 @@ struct bio {
 #define BIO_QUIET	6	/* Make BIO Quiet */
 #define BIO_CHAIN	7	/* chained bio, ->bi_remaining in effect */
 #define BIO_REFFED	8	/* bio has elevated ->bi_cnt */
+#define BIO_NONBLOCKING 9	/* don't block over blk device congestion */
 
 /*
  * Flags starting here get preserved by bio_reset() - this includes
-- 
2.10.2