On Tue, Feb 14, 2017 at 10:46 AM, Goldwyn Rodrigues <rgoldwyn@xxxxxxx> wrote:
> 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;
> + }
There are other places in which blocking may be triggered, such
as allocating for bio clone, wbt_wait(), and sleep in .make_request(),
like md, dm and bcache's.
IMO it should be hard to deal with all, so what is the expection for
flag of BIO_NONBLOCKING?
>
> 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
>
--
Ming Lei
