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* switch block layer polling to a bio based model v3
@ 2021-05-12 13:15 Christoph Hellwig
  2021-05-12 13:15 ` [PATCH 01/15] direct-io: remove blk_poll support Christoph Hellwig
                   ` (15 more replies)
  0 siblings, 16 replies; 40+ messages in thread
From: Christoph Hellwig @ 2021-05-12 13:15 UTC (permalink / raw)
  To: Jens Axboe
  Cc: Jeffle Xu, Ming Lei, Damien Le Moal, Keith Busch, Sagi Grimberg,
	Wunderlich, Mark, Vasudevan, Anil, linux-block, linux-fsdevel,
	linux-nvme

Hi all,

This series clean up the block polling code a bit and changes the interface
to poll for a specific bio instead of a request_queue and cookie pair.

Polling for the bio itself leads to a few advantages:

  - the cookie construction can made entirely private in blk-mq.c
  - the caller does not need to remember the request_queue and cookie
    separately and thus sidesteps their lifetime issues
  - keeping the device and the cookie inside the bio allows to trivially
    support polling BIOs remapping by stacking drivers
  - a lot of code to propagate the cookie back up the submission path can
    removed entirely

The one major caveat is that this requires RCU freeing polled BIOs to make
sure the bio that contains the polling information is still alive when
io_uring tries to poll it through the iocb. For synchronous polling all the
callers have a bio reference anyway, so this is not an issue.

Git tree:

   git://git.infradead.org/users/hch/block.git bio-poll

Gitweb:

    http://git.infradead.org/users/hch/block.git/shortlog/refs/heads/bio-poll

Chances since v2:
 - remove support for writing to the poll attribute
 - better document the block_device life time assumptions in bio_poll
 - only set QUEUE_FLAG_POLL on nvme-multipath queues where it makes sense

Chances since v1:
 - use SLAB_TYPESAFE_BY_RCU to only free the pages backing the bio
   slabs bio RCU
 - split the spin argument to bio_poll to avoid sleeping under RCU from
   io_uring
 - add support for polling nvme multipath devices

Diffstat:
 arch/m68k/emu/nfblock.c             |    3 
 arch/xtensa/platforms/iss/simdisk.c |    3 
 block/bio.c                         |    4 
 block/blk-core.c                    |  122 ++++++++++++++++++-------
 block/blk-merge.c                   |    2 
 block/blk-mq-debugfs.c              |    2 
 block/blk-mq.c                      |  173 ++++++++++++++----------------------
 block/blk-mq.h                      |    6 -
 block/blk-sysfs.c                   |   23 ----
 drivers/block/brd.c                 |   12 +-
 drivers/block/drbd/drbd_int.h       |    2 
 drivers/block/drbd/drbd_req.c       |    3 
 drivers/block/n64cart.c             |   12 +-
 drivers/block/null_blk/main.c       |    3 
 drivers/block/pktcdvd.c             |    7 -
 drivers/block/ps3vram.c             |    6 -
 drivers/block/rsxx/dev.c            |    7 -
 drivers/block/zram/zram_drv.c       |   10 --
 drivers/lightnvm/pblk-init.c        |    6 -
 drivers/md/bcache/request.c         |   13 +-
 drivers/md/bcache/request.h         |    4 
 drivers/md/dm.c                     |   28 ++---
 drivers/md/md.c                     |   10 --
 drivers/nvdimm/blk.c                |    5 -
 drivers/nvdimm/btt.c                |    5 -
 drivers/nvdimm/pmem.c               |    3 
 drivers/nvme/host/core.c            |    4 
 drivers/nvme/host/multipath.c       |   17 ++-
 drivers/s390/block/dcssblk.c        |    7 -
 drivers/s390/block/xpram.c          |    5 -
 fs/block_dev.c                      |   54 +++--------
 fs/btrfs/inode.c                    |    8 -
 fs/direct-io.c                      |   14 --
 fs/ext4/file.c                      |    2 
 fs/gfs2/file.c                      |    4 
 fs/io_uring.c                       |   14 +-
 fs/iomap/direct-io.c                |   56 ++++++-----
 fs/xfs/xfs_file.c                   |    2 
 fs/zonefs/super.c                   |    2 
 include/linux/bio.h                 |    4 
 include/linux/blk-mq.h              |   15 ---
 include/linux/blk_types.h           |   34 +------
 include/linux/blkdev.h              |   12 +-
 include/linux/bvec.h                |    2 
 include/linux/fs.h                  |    8 -
 include/linux/iomap.h               |    3 
 mm/page_io.c                        |   10 --
 47 files changed, 342 insertions(+), 409 deletions(-)

^ permalink raw reply	[flat|nested] 40+ messages in thread

* [PATCH 01/15] direct-io: remove blk_poll support
  2021-05-12 13:15 switch block layer polling to a bio based model v3 Christoph Hellwig
@ 2021-05-12 13:15 ` Christoph Hellwig
  2021-05-12 13:15 ` [PATCH 02/15] block: don't try to poll multi-bio I/Os in __blkdev_direct_IO Christoph Hellwig
                   ` (14 subsequent siblings)
  15 siblings, 0 replies; 40+ messages in thread
From: Christoph Hellwig @ 2021-05-12 13:15 UTC (permalink / raw)
  To: Jens Axboe
  Cc: Jeffle Xu, Ming Lei, Damien Le Moal, Keith Busch, Sagi Grimberg,
	Wunderlich, Mark, Vasudevan, Anil, linux-block, linux-fsdevel,
	linux-nvme

The polling support in the legacy direct-io support is a little crufty.
It already doesn't support the asynchronous polling needed for io_uring
polling, and is hard to adopt to upcoming changes in the polling
interfaces.  Given that all the major file systems already use the iomap
direct I/O code, just drop the polling support.

Signed-off-by: Christoph Hellwig <hch@lst.de>
---
 fs/direct-io.c | 14 ++++----------
 1 file changed, 4 insertions(+), 10 deletions(-)

diff --git a/fs/direct-io.c b/fs/direct-io.c
index b2e86e739d7a..453dcff0e7f5 100644
--- a/fs/direct-io.c
+++ b/fs/direct-io.c
@@ -119,7 +119,6 @@ struct dio {
 	int flags;			/* doesn't change */
 	int op;
 	int op_flags;
-	blk_qc_t bio_cookie;
 	struct gendisk *bio_disk;
 	struct inode *inode;
 	loff_t i_size;			/* i_size when submitted */
@@ -438,11 +437,10 @@ static inline void dio_bio_submit(struct dio *dio, struct dio_submit *sdio)
 
 	dio->bio_disk = bio->bi_bdev->bd_disk;
 
-	if (sdio->submit_io) {
+	if (sdio->submit_io)
 		sdio->submit_io(bio, dio->inode, sdio->logical_offset_in_bio);
-		dio->bio_cookie = BLK_QC_T_NONE;
-	} else
-		dio->bio_cookie = submit_bio(bio);
+	else
+		submit_bio(bio);
 
 	sdio->bio = NULL;
 	sdio->boundary = 0;
@@ -481,9 +479,7 @@ static struct bio *dio_await_one(struct dio *dio)
 		__set_current_state(TASK_UNINTERRUPTIBLE);
 		dio->waiter = current;
 		spin_unlock_irqrestore(&dio->bio_lock, flags);
-		if (!(dio->iocb->ki_flags & IOCB_HIPRI) ||
-		    !blk_poll(dio->bio_disk->queue, dio->bio_cookie, true))
-			blk_io_schedule();
+		blk_io_schedule();
 		/* wake up sets us TASK_RUNNING */
 		spin_lock_irqsave(&dio->bio_lock, flags);
 		dio->waiter = NULL;
@@ -1214,8 +1210,6 @@ do_blockdev_direct_IO(struct kiocb *iocb, struct inode *inode,
 	} else {
 		dio->op = REQ_OP_READ;
 	}
-	if (iocb->ki_flags & IOCB_HIPRI)
-		dio->op_flags |= REQ_HIPRI;
 
 	/*
 	 * For AIO O_(D)SYNC writes we need to defer completions to a workqueue
-- 
2.30.2


^ permalink raw reply	[flat|nested] 40+ messages in thread

* [PATCH 02/15] block: don't try to poll multi-bio I/Os in __blkdev_direct_IO
  2021-05-12 13:15 switch block layer polling to a bio based model v3 Christoph Hellwig
  2021-05-12 13:15 ` [PATCH 01/15] direct-io: remove blk_poll support Christoph Hellwig
@ 2021-05-12 13:15 ` Christoph Hellwig
  2021-05-12 20:54   ` Sagi Grimberg
  2021-05-16 18:01   ` Kanchan Joshi
  2021-05-12 13:15 ` [PATCH 03/15] iomap: don't try to poll multi-bio I/Os in __iomap_dio_rw Christoph Hellwig
                   ` (13 subsequent siblings)
  15 siblings, 2 replies; 40+ messages in thread
From: Christoph Hellwig @ 2021-05-12 13:15 UTC (permalink / raw)
  To: Jens Axboe
  Cc: Jeffle Xu, Ming Lei, Damien Le Moal, Keith Busch, Sagi Grimberg,
	Wunderlich, Mark, Vasudevan, Anil, linux-block, linux-fsdevel,
	linux-nvme

If an iocb is split into multiple bios we can't poll for both.  So don't
bother to even try to poll in that case.

Signed-off-by: Christoph Hellwig <hch@lst.de>
---
 fs/block_dev.c | 37 ++++++++++++++-----------------------
 1 file changed, 14 insertions(+), 23 deletions(-)

diff --git a/fs/block_dev.c b/fs/block_dev.c
index b8abccd03e5d..0080a3b710b4 100644
--- a/fs/block_dev.c
+++ b/fs/block_dev.c
@@ -375,7 +375,7 @@ static ssize_t __blkdev_direct_IO(struct kiocb *iocb, struct iov_iter *iter,
 	struct blk_plug plug;
 	struct blkdev_dio *dio;
 	struct bio *bio;
-	bool is_poll = (iocb->ki_flags & IOCB_HIPRI) != 0;
+	bool is_poll = (iocb->ki_flags & IOCB_HIPRI), do_poll = false;
 	bool is_read = (iov_iter_rw(iter) == READ), is_sync;
 	loff_t pos = iocb->ki_pos;
 	blk_qc_t qc = BLK_QC_T_NONE;
@@ -437,22 +437,9 @@ static ssize_t __blkdev_direct_IO(struct kiocb *iocb, struct iov_iter *iter,
 		pos += bio->bi_iter.bi_size;
 
 		nr_pages = bio_iov_vecs_to_alloc(iter, BIO_MAX_VECS);
-		if (!nr_pages) {
-			bool polled = false;
-
-			if (iocb->ki_flags & IOCB_HIPRI) {
-				bio_set_polled(bio, iocb);
-				polled = true;
-			}
-
-			qc = submit_bio(bio);
-
-			if (polled)
-				WRITE_ONCE(iocb->ki_cookie, qc);
-			break;
-		}
-
-		if (!dio->multi_bio) {
+		if (dio->multi_bio) {
+			atomic_inc(&dio->ref);
+		} else if (nr_pages) {
 			/*
 			 * AIO needs an extra reference to ensure the dio
 			 * structure which is embedded into the first bio
@@ -462,11 +449,16 @@ static ssize_t __blkdev_direct_IO(struct kiocb *iocb, struct iov_iter *iter,
 				bio_get(bio);
 			dio->multi_bio = true;
 			atomic_set(&dio->ref, 2);
-		} else {
-			atomic_inc(&dio->ref);
+		} else if (is_poll) {
+			bio_set_polled(bio, iocb);
+			do_poll = true;
+		}
+		qc = submit_bio(bio);
+		if (!nr_pages) {
+			if (do_poll)
+				WRITE_ONCE(iocb->ki_cookie, qc);
+			break;
 		}
-
-		submit_bio(bio);
 		bio = bio_alloc(GFP_KERNEL, nr_pages);
 	}
 
@@ -481,8 +473,7 @@ static ssize_t __blkdev_direct_IO(struct kiocb *iocb, struct iov_iter *iter,
 		if (!READ_ONCE(dio->waiter))
 			break;
 
-		if (!(iocb->ki_flags & IOCB_HIPRI) ||
-		    !blk_poll(bdev_get_queue(bdev), qc, true))
+		if (!do_poll || !blk_poll(bdev_get_queue(bdev), qc, true))
 			blk_io_schedule();
 	}
 	__set_current_state(TASK_RUNNING);
-- 
2.30.2


^ permalink raw reply	[flat|nested] 40+ messages in thread

* [PATCH 03/15] iomap: don't try to poll multi-bio I/Os in __iomap_dio_rw
  2021-05-12 13:15 switch block layer polling to a bio based model v3 Christoph Hellwig
  2021-05-12 13:15 ` [PATCH 01/15] direct-io: remove blk_poll support Christoph Hellwig
  2021-05-12 13:15 ` [PATCH 02/15] block: don't try to poll multi-bio I/Os in __blkdev_direct_IO Christoph Hellwig
@ 2021-05-12 13:15 ` Christoph Hellwig
  2021-05-12 21:32   ` Darrick J. Wong
  2021-05-12 13:15 ` [PATCH 04/15] blk-mq: factor out a blk_qc_to_hctx helper Christoph Hellwig
                   ` (12 subsequent siblings)
  15 siblings, 1 reply; 40+ messages in thread
From: Christoph Hellwig @ 2021-05-12 13:15 UTC (permalink / raw)
  To: Jens Axboe
  Cc: Jeffle Xu, Ming Lei, Damien Le Moal, Keith Busch, Sagi Grimberg,
	Wunderlich, Mark, Vasudevan, Anil, linux-block, linux-fsdevel,
	linux-nvme

If an iocb is split into multiple bios we can't poll for both.  So don't
bother to even try to poll in that case.

Signed-off-by: Christoph Hellwig <hch@lst.de>
---
 fs/iomap/direct-io.c | 17 +++++++++++++++++
 1 file changed, 17 insertions(+)

diff --git a/fs/iomap/direct-io.c b/fs/iomap/direct-io.c
index 9398b8c31323..d5637f467109 100644
--- a/fs/iomap/direct-io.c
+++ b/fs/iomap/direct-io.c
@@ -282,6 +282,13 @@ iomap_dio_bio_actor(struct inode *inode, loff_t pos, loff_t length,
 	if (!iov_iter_count(dio->submit.iter))
 		goto out;
 
+	/*
+	 * We can only poll for single bio I/Os.
+	 */
+	if (need_zeroout ||
+	    ((dio->flags & IOMAP_DIO_WRITE) && pos >= i_size_read(inode)))
+		dio->iocb->ki_flags &= ~IOCB_HIPRI;
+
 	if (need_zeroout) {
 		/* zero out from the start of the block to the write offset */
 		pad = pos & (fs_block_size - 1);
@@ -339,6 +346,11 @@ iomap_dio_bio_actor(struct inode *inode, loff_t pos, loff_t length,
 
 		nr_pages = bio_iov_vecs_to_alloc(dio->submit.iter,
 						 BIO_MAX_VECS);
+		/*
+		 * We can only poll for single bio I/Os.
+		 */
+		if (nr_pages)
+			dio->iocb->ki_flags &= ~IOCB_HIPRI;
 		iomap_dio_submit_bio(dio, iomap, bio, pos);
 		pos += n;
 	} while (nr_pages);
@@ -579,6 +591,11 @@ __iomap_dio_rw(struct kiocb *iocb, struct iov_iter *iter,
 			iov_iter_revert(iter, pos - dio->i_size);
 			break;
 		}
+
+		/*
+		 * We can only poll for single bio I/Os.
+		 */
+		iocb->ki_flags &= ~IOCB_HIPRI;
 	} while ((count = iov_iter_count(iter)) > 0);
 	blk_finish_plug(&plug);
 
-- 
2.30.2


^ permalink raw reply	[flat|nested] 40+ messages in thread

* [PATCH 04/15] blk-mq: factor out a blk_qc_to_hctx helper
  2021-05-12 13:15 switch block layer polling to a bio based model v3 Christoph Hellwig
                   ` (2 preceding siblings ...)
  2021-05-12 13:15 ` [PATCH 03/15] iomap: don't try to poll multi-bio I/Os in __iomap_dio_rw Christoph Hellwig
@ 2021-05-12 13:15 ` Christoph Hellwig
  2021-05-12 20:58   ` Sagi Grimberg
  2021-05-12 13:15 ` [PATCH 05/15] blk-mq: factor out a "classic" poll helper Christoph Hellwig
                   ` (11 subsequent siblings)
  15 siblings, 1 reply; 40+ messages in thread
From: Christoph Hellwig @ 2021-05-12 13:15 UTC (permalink / raw)
  To: Jens Axboe
  Cc: Jeffle Xu, Ming Lei, Damien Le Moal, Keith Busch, Sagi Grimberg,
	Wunderlich, Mark, Vasudevan, Anil, linux-block, linux-fsdevel,
	linux-nvme

Add a helper to get the hctx from a request_queue and cookie, and fold
the blk_qc_t_to_queue_num helper into it as no other callers are left.

Signed-off-by: Christoph Hellwig <hch@lst.de>
---
 block/blk-mq.c            | 8 +++++++-
 include/linux/blk_types.h | 5 -----
 2 files changed, 7 insertions(+), 6 deletions(-)

diff --git a/block/blk-mq.c b/block/blk-mq.c
index 466676bc2f0b..04e17d50fb02 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -63,6 +63,12 @@ static int blk_mq_poll_stats_bkt(const struct request *rq)
 	return bucket;
 }
 
+static inline struct blk_mq_hw_ctx *blk_qc_to_hctx(struct request_queue *q,
+		blk_qc_t qc)
+{
+	return q->queue_hw_ctx[(qc & ~BLK_QC_T_INTERNAL) >> BLK_QC_T_SHIFT];
+}
+
 /*
  * Check if any of the ctx, dispatch list or elevator
  * have pending work in this hardware queue.
@@ -3892,7 +3898,7 @@ int blk_poll(struct request_queue *q, blk_qc_t cookie, bool spin)
 	if (current->plug)
 		blk_flush_plug_list(current->plug, false);
 
-	hctx = q->queue_hw_ctx[blk_qc_t_to_queue_num(cookie)];
+	hctx = blk_qc_to_hctx(q, cookie);
 
 	/*
 	 * If we sleep, have the caller restart the poll loop to reset
diff --git a/include/linux/blk_types.h b/include/linux/blk_types.h
index db026b6ec15a..ed71a8d968f2 100644
--- a/include/linux/blk_types.h
+++ b/include/linux/blk_types.h
@@ -515,11 +515,6 @@ static inline bool blk_qc_t_valid(blk_qc_t cookie)
 	return cookie != BLK_QC_T_NONE;
 }
 
-static inline unsigned int blk_qc_t_to_queue_num(blk_qc_t cookie)
-{
-	return (cookie & ~BLK_QC_T_INTERNAL) >> BLK_QC_T_SHIFT;
-}
-
 static inline unsigned int blk_qc_t_to_tag(blk_qc_t cookie)
 {
 	return cookie & ((1u << BLK_QC_T_SHIFT) - 1);
-- 
2.30.2


^ permalink raw reply	[flat|nested] 40+ messages in thread

* [PATCH 05/15] blk-mq: factor out a "classic" poll helper
  2021-05-12 13:15 switch block layer polling to a bio based model v3 Christoph Hellwig
                   ` (3 preceding siblings ...)
  2021-05-12 13:15 ` [PATCH 04/15] blk-mq: factor out a blk_qc_to_hctx helper Christoph Hellwig
@ 2021-05-12 13:15 ` Christoph Hellwig
  2021-05-12 20:59   ` Sagi Grimberg
  2021-05-12 13:15 ` [PATCH 06/15] blk-mq: remove blk_qc_t_to_tag and blk_qc_t_is_internal Christoph Hellwig
                   ` (10 subsequent siblings)
  15 siblings, 1 reply; 40+ messages in thread
From: Christoph Hellwig @ 2021-05-12 13:15 UTC (permalink / raw)
  To: Jens Axboe
  Cc: Jeffle Xu, Ming Lei, Damien Le Moal, Keith Busch, Sagi Grimberg,
	Wunderlich, Mark, Vasudevan, Anil, linux-block, linux-fsdevel,
	linux-nvme

Factor the code to do the classic full metal polling out of blk_poll into
a separate blk_mq_poll_classic helper.

Signed-off-by: Christoph Hellwig <hch@lst.de>
---
 block/blk-mq.c | 120 +++++++++++++++++++++++--------------------------
 1 file changed, 56 insertions(+), 64 deletions(-)

diff --git a/block/blk-mq.c b/block/blk-mq.c
index 04e17d50fb02..72d5559e4bba 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -69,6 +69,14 @@ static inline struct blk_mq_hw_ctx *blk_qc_to_hctx(struct request_queue *q,
 	return q->queue_hw_ctx[(qc & ~BLK_QC_T_INTERNAL) >> BLK_QC_T_SHIFT];
 }
 
+static inline struct request *blk_qc_to_rq(struct blk_mq_hw_ctx *hctx,
+		blk_qc_t qc)
+{
+	if (blk_qc_t_is_internal(qc))
+		return blk_mq_tag_to_rq(hctx->sched_tags, blk_qc_t_to_tag(qc));
+	return blk_mq_tag_to_rq(hctx->tags, blk_qc_t_to_tag(qc));
+}
+
 /*
  * Check if any of the ctx, dispatch list or elevator
  * have pending work in this hardware queue.
@@ -3796,15 +3804,20 @@ static unsigned long blk_mq_poll_nsecs(struct request_queue *q,
 	return ret;
 }
 
-static bool blk_mq_poll_hybrid_sleep(struct request_queue *q,
-				     struct request *rq)
+static bool blk_mq_poll_hybrid(struct request_queue *q, blk_qc_t qc)
 {
+	struct blk_mq_hw_ctx *hctx = blk_qc_to_hctx(q, qc);
+	struct request *rq = blk_qc_to_rq(hctx, qc);
 	struct hrtimer_sleeper hs;
 	enum hrtimer_mode mode;
 	unsigned int nsecs;
 	ktime_t kt;
 
-	if (rq->rq_flags & RQF_MQ_POLL_SLEPT)
+	/*
+	 * If a request has completed on queue that uses an I/O scheduler, we
+	 * won't get back a request from blk_qc_to_rq.
+	 */
+	if (!rq || (rq->rq_flags & RQF_MQ_POLL_SLEPT))
 		return false;
 
 	/*
@@ -3846,32 +3859,48 @@ static bool blk_mq_poll_hybrid_sleep(struct request_queue *q,
 
 	__set_current_state(TASK_RUNNING);
 	destroy_hrtimer_on_stack(&hs.timer);
+
+	/*
+	 * If we sleep, have the caller restart the poll loop to reset the
+	 * state.  Like for the other success return cases, the caller is
+	 * responsible for checking if the IO completed.  If the IO isn't
+	 * complete, we'll get called again and will go straight to the busy
+	 * poll loop.
+	 */
 	return true;
 }
 
-static bool blk_mq_poll_hybrid(struct request_queue *q,
-			       struct blk_mq_hw_ctx *hctx, blk_qc_t cookie)
+static int blk_mq_poll_classic(struct request_queue *q, blk_qc_t cookie,
+		bool spin)
 {
-	struct request *rq;
+	struct blk_mq_hw_ctx *hctx = blk_qc_to_hctx(q, cookie);
+	long state = current->state;
+	int ret;
 
-	if (q->poll_nsec == BLK_MQ_POLL_CLASSIC)
-		return false;
+	hctx->poll_considered++;
 
-	if (!blk_qc_t_is_internal(cookie))
-		rq = blk_mq_tag_to_rq(hctx->tags, blk_qc_t_to_tag(cookie));
-	else {
-		rq = blk_mq_tag_to_rq(hctx->sched_tags, blk_qc_t_to_tag(cookie));
-		/*
-		 * With scheduling, if the request has completed, we'll
-		 * get a NULL return here, as we clear the sched tag when
-		 * that happens. The request still remains valid, like always,
-		 * so we should be safe with just the NULL check.
-		 */
-		if (!rq)
-			return false;
-	}
+	do {
+		hctx->poll_invoked++;
 
-	return blk_mq_poll_hybrid_sleep(q, rq);
+		ret = q->mq_ops->poll(hctx);
+		if (ret > 0) {
+			hctx->poll_success++;
+			__set_current_state(TASK_RUNNING);
+			return ret;
+		}
+
+		if (signal_pending_state(state, current))
+			__set_current_state(TASK_RUNNING);
+		if (current->state == TASK_RUNNING)
+			return 1;
+
+		if (ret < 0 || !spin)
+			break;
+		cpu_relax();
+	} while (!need_resched());
+
+	__set_current_state(TASK_RUNNING);
+	return 0;
 }
 
 /**
@@ -3888,9 +3917,6 @@ static bool blk_mq_poll_hybrid(struct request_queue *q,
  */
 int blk_poll(struct request_queue *q, blk_qc_t cookie, bool spin)
 {
-	struct blk_mq_hw_ctx *hctx;
-	long state;
-
 	if (!blk_qc_t_valid(cookie) ||
 	    !test_bit(QUEUE_FLAG_POLL, &q->queue_flags))
 		return 0;
@@ -3898,46 +3924,12 @@ int blk_poll(struct request_queue *q, blk_qc_t cookie, bool spin)
 	if (current->plug)
 		blk_flush_plug_list(current->plug, false);
 
-	hctx = blk_qc_to_hctx(q, cookie);
-
-	/*
-	 * If we sleep, have the caller restart the poll loop to reset
-	 * the state. Like for the other success return cases, the
-	 * caller is responsible for checking if the IO completed. If
-	 * the IO isn't complete, we'll get called again and will go
-	 * straight to the busy poll loop. If specified not to spin,
-	 * we also should not sleep.
-	 */
-	if (spin && blk_mq_poll_hybrid(q, hctx, cookie))
-		return 1;
-
-	hctx->poll_considered++;
-
-	state = current->state;
-	do {
-		int ret;
-
-		hctx->poll_invoked++;
-
-		ret = q->mq_ops->poll(hctx);
-		if (ret > 0) {
-			hctx->poll_success++;
-			__set_current_state(TASK_RUNNING);
-			return ret;
-		}
-
-		if (signal_pending_state(state, current))
-			__set_current_state(TASK_RUNNING);
-
-		if (current->state == TASK_RUNNING)
+	/* If specified not to spin, we also should not sleep. */
+	if (spin && q->poll_nsec != BLK_MQ_POLL_CLASSIC) {
+		if (blk_mq_poll_hybrid(q, cookie))
 			return 1;
-		if (ret < 0 || !spin)
-			break;
-		cpu_relax();
-	} while (!need_resched());
-
-	__set_current_state(TASK_RUNNING);
-	return 0;
+	}
+	return blk_mq_poll_classic(q, cookie, spin);
 }
 EXPORT_SYMBOL_GPL(blk_poll);
 
-- 
2.30.2


^ permalink raw reply	[flat|nested] 40+ messages in thread

* [PATCH 06/15] blk-mq: remove blk_qc_t_to_tag and blk_qc_t_is_internal
  2021-05-12 13:15 switch block layer polling to a bio based model v3 Christoph Hellwig
                   ` (4 preceding siblings ...)
  2021-05-12 13:15 ` [PATCH 05/15] blk-mq: factor out a "classic" poll helper Christoph Hellwig
@ 2021-05-12 13:15 ` Christoph Hellwig
  2021-05-12 21:42   ` Sagi Grimberg
  2021-05-12 13:15 ` [PATCH 07/15] blk-mq: remove blk_qc_t_valid Christoph Hellwig
                   ` (9 subsequent siblings)
  15 siblings, 1 reply; 40+ messages in thread
From: Christoph Hellwig @ 2021-05-12 13:15 UTC (permalink / raw)
  To: Jens Axboe
  Cc: Jeffle Xu, Ming Lei, Damien Le Moal, Keith Busch, Sagi Grimberg,
	Wunderlich, Mark, Vasudevan, Anil, linux-block, linux-fsdevel,
	linux-nvme

Merge both functions into their only caller to keep the blk-mq tag to
blk_qc_t mapping as private as possible in blk-mq.c.

Signed-off-by: Christoph Hellwig <hch@lst.de>
---
 block/blk-mq.c            |  8 +++++---
 include/linux/blk_types.h | 10 ----------
 2 files changed, 5 insertions(+), 13 deletions(-)

diff --git a/block/blk-mq.c b/block/blk-mq.c
index 72d5559e4bba..919712e2b34c 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -72,9 +72,11 @@ static inline struct blk_mq_hw_ctx *blk_qc_to_hctx(struct request_queue *q,
 static inline struct request *blk_qc_to_rq(struct blk_mq_hw_ctx *hctx,
 		blk_qc_t qc)
 {
-	if (blk_qc_t_is_internal(qc))
-		return blk_mq_tag_to_rq(hctx->sched_tags, blk_qc_t_to_tag(qc));
-	return blk_mq_tag_to_rq(hctx->tags, blk_qc_t_to_tag(qc));
+	unsigned int tag = qc & ((1U << BLK_QC_T_SHIFT) - 1);
+
+	if (qc & BLK_QC_T_INTERNAL)
+		return blk_mq_tag_to_rq(hctx->sched_tags, tag);
+	return blk_mq_tag_to_rq(hctx->tags, tag);
 }
 
 /*
diff --git a/include/linux/blk_types.h b/include/linux/blk_types.h
index ed71a8d968f2..4c28ab22f93d 100644
--- a/include/linux/blk_types.h
+++ b/include/linux/blk_types.h
@@ -515,16 +515,6 @@ static inline bool blk_qc_t_valid(blk_qc_t cookie)
 	return cookie != BLK_QC_T_NONE;
 }
 
-static inline unsigned int blk_qc_t_to_tag(blk_qc_t cookie)
-{
-	return cookie & ((1u << BLK_QC_T_SHIFT) - 1);
-}
-
-static inline bool blk_qc_t_is_internal(blk_qc_t cookie)
-{
-	return (cookie & BLK_QC_T_INTERNAL) != 0;
-}
-
 struct blk_rq_stat {
 	u64 mean;
 	u64 min;
-- 
2.30.2


^ permalink raw reply	[flat|nested] 40+ messages in thread

* [PATCH 07/15] blk-mq: remove blk_qc_t_valid
  2021-05-12 13:15 switch block layer polling to a bio based model v3 Christoph Hellwig
                   ` (5 preceding siblings ...)
  2021-05-12 13:15 ` [PATCH 06/15] blk-mq: remove blk_qc_t_to_tag and blk_qc_t_is_internal Christoph Hellwig
@ 2021-05-12 13:15 ` Christoph Hellwig
  2021-05-12 21:43   ` Sagi Grimberg
  2021-05-12 13:15 ` [PATCH 08/15] io_uring: don't sleep when polling for I/O Christoph Hellwig
                   ` (8 subsequent siblings)
  15 siblings, 1 reply; 40+ messages in thread
From: Christoph Hellwig @ 2021-05-12 13:15 UTC (permalink / raw)
  To: Jens Axboe
  Cc: Jeffle Xu, Ming Lei, Damien Le Moal, Keith Busch, Sagi Grimberg,
	Wunderlich, Mark, Vasudevan, Anil, linux-block, linux-fsdevel,
	linux-nvme

Move the trivial check into the only caller.

Signed-off-by: Christoph Hellwig <hch@lst.de>
---
 block/blk-mq.c            | 2 +-
 include/linux/blk_types.h | 5 -----
 2 files changed, 1 insertion(+), 6 deletions(-)

diff --git a/block/blk-mq.c b/block/blk-mq.c
index 919712e2b34c..ac0b517c5503 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -3919,7 +3919,7 @@ static int blk_mq_poll_classic(struct request_queue *q, blk_qc_t cookie,
  */
 int blk_poll(struct request_queue *q, blk_qc_t cookie, bool spin)
 {
-	if (!blk_qc_t_valid(cookie) ||
+	if (cookie == BLK_QC_T_NONE ||
 	    !test_bit(QUEUE_FLAG_POLL, &q->queue_flags))
 		return 0;
 
diff --git a/include/linux/blk_types.h b/include/linux/blk_types.h
index 4c28ab22f93d..d0cf835d3b50 100644
--- a/include/linux/blk_types.h
+++ b/include/linux/blk_types.h
@@ -510,11 +510,6 @@ typedef unsigned int blk_qc_t;
 #define BLK_QC_T_SHIFT		16
 #define BLK_QC_T_INTERNAL	(1U << 31)
 
-static inline bool blk_qc_t_valid(blk_qc_t cookie)
-{
-	return cookie != BLK_QC_T_NONE;
-}
-
 struct blk_rq_stat {
 	u64 mean;
 	u64 min;
-- 
2.30.2


^ permalink raw reply	[flat|nested] 40+ messages in thread

* [PATCH 08/15] io_uring: don't sleep when polling for I/O
  2021-05-12 13:15 switch block layer polling to a bio based model v3 Christoph Hellwig
                   ` (6 preceding siblings ...)
  2021-05-12 13:15 ` [PATCH 07/15] blk-mq: remove blk_qc_t_valid Christoph Hellwig
@ 2021-05-12 13:15 ` Christoph Hellwig
  2021-05-12 21:55   ` Sagi Grimberg
  2021-05-12 13:15 ` [PATCH 09/15] block: rename REQ_HIPRI to REQ_POLLED Christoph Hellwig
                   ` (7 subsequent siblings)
  15 siblings, 1 reply; 40+ messages in thread
From: Christoph Hellwig @ 2021-05-12 13:15 UTC (permalink / raw)
  To: Jens Axboe
  Cc: Jeffle Xu, Ming Lei, Damien Le Moal, Keith Busch, Sagi Grimberg,
	Wunderlich, Mark, Vasudevan, Anil, linux-block, linux-fsdevel,
	linux-nvme

There is no point in sleeping for the expected I/O completion timeout
in the io_uring async polling model as we never poll for a specific
I/O.  Split the boolean spin argument to blk_poll into a set of flags
to control sleeping and the oneshot behavior separately.

Signed-off-by: Christoph Hellwig <hch@lst.de>
---
 block/blk-mq.c           | 18 ++++++++----------
 drivers/nvme/host/core.c |  2 +-
 fs/block_dev.c           |  8 ++++----
 fs/io_uring.c            | 14 +++++++-------
 fs/iomap/direct-io.c     |  6 +++---
 include/linux/blkdev.h   |  6 +++++-
 include/linux/fs.h       |  2 +-
 include/linux/iomap.h    |  2 +-
 mm/page_io.c             |  2 +-
 9 files changed, 31 insertions(+), 29 deletions(-)

diff --git a/block/blk-mq.c b/block/blk-mq.c
index ac0b517c5503..164e39d34bf6 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -3873,7 +3873,7 @@ static bool blk_mq_poll_hybrid(struct request_queue *q, blk_qc_t qc)
 }
 
 static int blk_mq_poll_classic(struct request_queue *q, blk_qc_t cookie,
-		bool spin)
+		unsigned int flags)
 {
 	struct blk_mq_hw_ctx *hctx = blk_qc_to_hctx(q, cookie);
 	long state = current->state;
@@ -3896,7 +3896,7 @@ static int blk_mq_poll_classic(struct request_queue *q, blk_qc_t cookie,
 		if (current->state == TASK_RUNNING)
 			return 1;
 
-		if (ret < 0 || !spin)
+		if (ret < 0 || (flags & BLK_POLL_ONESHOT))
 			break;
 		cpu_relax();
 	} while (!need_resched());
@@ -3909,15 +3909,13 @@ static int blk_mq_poll_classic(struct request_queue *q, blk_qc_t cookie,
  * blk_poll - poll for IO completions
  * @q:  the queue
  * @cookie: cookie passed back at IO submission time
- * @spin: whether to spin for completions
+ * @flags: BLK_POLL_* flags that control the behavior
  *
  * Description:
  *    Poll for completions on the passed in queue. Returns number of
- *    completed entries found. If @spin is true, then blk_poll will continue
- *    looping until at least one completion is found, unless the task is
- *    otherwise marked running (or we need to reschedule).
+ *    completed entries found.
  */
-int blk_poll(struct request_queue *q, blk_qc_t cookie, bool spin)
+int blk_poll(struct request_queue *q, blk_qc_t cookie, unsigned int flags)
 {
 	if (cookie == BLK_QC_T_NONE ||
 	    !test_bit(QUEUE_FLAG_POLL, &q->queue_flags))
@@ -3926,12 +3924,12 @@ int blk_poll(struct request_queue *q, blk_qc_t cookie, bool spin)
 	if (current->plug)
 		blk_flush_plug_list(current->plug, false);
 
-	/* If specified not to spin, we also should not sleep. */
-	if (spin && q->poll_nsec != BLK_MQ_POLL_CLASSIC) {
+	if (!(flags & BLK_POLL_NOSLEEP) &&
+	    q->poll_nsec != BLK_MQ_POLL_CLASSIC) {
 		if (blk_mq_poll_hybrid(q, cookie))
 			return 1;
 	}
-	return blk_mq_poll_classic(q, cookie, spin);
+	return blk_mq_poll_classic(q, cookie, flags);
 }
 EXPORT_SYMBOL_GPL(blk_poll);
 
diff --git a/drivers/nvme/host/core.c b/drivers/nvme/host/core.c
index 522c9b229f80..8fa7e90020b0 100644
--- a/drivers/nvme/host/core.c
+++ b/drivers/nvme/host/core.c
@@ -1032,7 +1032,7 @@ static void nvme_execute_rq_polled(struct request_queue *q,
 	blk_execute_rq_nowait(bd_disk, rq, at_head, nvme_end_sync_rq);
 
 	while (!completion_done(&wait)) {
-		blk_poll(q, request_to_qc_t(rq->mq_hctx, rq), true);
+		blk_poll(q, request_to_qc_t(rq->mq_hctx, rq), 0);
 		cond_resched();
 	}
 }
diff --git a/fs/block_dev.c b/fs/block_dev.c
index 0080a3b710b4..fd12a05cb3a9 100644
--- a/fs/block_dev.c
+++ b/fs/block_dev.c
@@ -286,7 +286,7 @@ __blkdev_direct_IO_simple(struct kiocb *iocb, struct iov_iter *iter,
 		if (!READ_ONCE(bio.bi_private))
 			break;
 		if (!(iocb->ki_flags & IOCB_HIPRI) ||
-		    !blk_poll(bdev_get_queue(bdev), qc, true))
+		    !blk_poll(bdev_get_queue(bdev), qc, 0))
 			blk_io_schedule();
 	}
 	__set_current_state(TASK_RUNNING);
@@ -319,12 +319,12 @@ struct blkdev_dio {
 
 static struct bio_set blkdev_dio_pool;
 
-static int blkdev_iopoll(struct kiocb *kiocb, bool wait)
+static int blkdev_iopoll(struct kiocb *kiocb, unsigned int flags)
 {
 	struct block_device *bdev = I_BDEV(kiocb->ki_filp->f_mapping->host);
 	struct request_queue *q = bdev_get_queue(bdev);
 
-	return blk_poll(q, READ_ONCE(kiocb->ki_cookie), wait);
+	return blk_poll(q, READ_ONCE(kiocb->ki_cookie), flags);
 }
 
 static void blkdev_bio_end_io(struct bio *bio)
@@ -473,7 +473,7 @@ static ssize_t __blkdev_direct_IO(struct kiocb *iocb, struct iov_iter *iter,
 		if (!READ_ONCE(dio->waiter))
 			break;
 
-		if (!do_poll || !blk_poll(bdev_get_queue(bdev), qc, true))
+		if (!do_poll || !blk_poll(bdev_get_queue(bdev), qc, 0))
 			blk_io_schedule();
 	}
 	__set_current_state(TASK_RUNNING);
diff --git a/fs/io_uring.c b/fs/io_uring.c
index f46acbbeed57..7baa88abe630 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -2288,18 +2288,18 @@ static void io_iopoll_complete(struct io_ring_ctx *ctx, unsigned int *nr_events,
 static int io_do_iopoll(struct io_ring_ctx *ctx, unsigned int *nr_events,
 			long min)
 {
+	unsigned int poll_flags = BLK_POLL_NOSLEEP;
 	struct io_kiocb *req, *tmp;
 	LIST_HEAD(done);
-	bool spin;
-	int ret;
+	int ret = 0;
 
 	/*
 	 * Only spin for completions if we don't have multiple devices hanging
 	 * off our complete list, and we're under the requested amount.
 	 */
-	spin = !ctx->poll_multi_file && *nr_events < min;
+	if (ctx->poll_multi_file || *nr_events >= min)
+		poll_flags |= BLK_POLL_ONESHOT;
 
-	ret = 0;
 	list_for_each_entry_safe(req, tmp, &ctx->iopoll_list, inflight_entry) {
 		struct kiocb *kiocb = &req->rw.kiocb;
 
@@ -2315,7 +2315,7 @@ static int io_do_iopoll(struct io_ring_ctx *ctx, unsigned int *nr_events,
 		if (!list_empty(&done))
 			break;
 
-		ret = kiocb->ki_filp->f_op->iopoll(kiocb, spin);
+		ret = kiocb->ki_filp->f_op->iopoll(kiocb, poll_flags);
 		if (ret < 0)
 			break;
 
@@ -2323,8 +2323,8 @@ static int io_do_iopoll(struct io_ring_ctx *ctx, unsigned int *nr_events,
 		if (READ_ONCE(req->iopoll_completed))
 			list_move_tail(&req->inflight_entry, &done);
 
-		if (ret && spin)
-			spin = false;
+		if (ret)
+			poll_flags |= BLK_POLL_ONESHOT;
 		ret = 0;
 	}
 
diff --git a/fs/iomap/direct-io.c b/fs/iomap/direct-io.c
index d5637f467109..9b6c26da3a2d 100644
--- a/fs/iomap/direct-io.c
+++ b/fs/iomap/direct-io.c
@@ -49,13 +49,13 @@ struct iomap_dio {
 	};
 };
 
-int iomap_dio_iopoll(struct kiocb *kiocb, bool spin)
+int iomap_dio_iopoll(struct kiocb *kiocb, unsigned int flags)
 {
 	struct request_queue *q = READ_ONCE(kiocb->private);
 
 	if (!q)
 		return 0;
-	return blk_poll(q, READ_ONCE(kiocb->ki_cookie), spin);
+	return blk_poll(q, READ_ONCE(kiocb->ki_cookie), flags);
 }
 EXPORT_SYMBOL_GPL(iomap_dio_iopoll);
 
@@ -640,7 +640,7 @@ __iomap_dio_rw(struct kiocb *iocb, struct iov_iter *iter,
 			if (!(iocb->ki_flags & IOCB_HIPRI) ||
 			    !dio->submit.last_queue ||
 			    !blk_poll(dio->submit.last_queue,
-					 dio->submit.cookie, true))
+					 dio->submit.cookie, 0))
 				blk_io_schedule();
 		}
 		__set_current_state(TASK_RUNNING);
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index 1255823b2bc0..273b86714c7e 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -947,7 +947,11 @@ extern const char *blk_op_str(unsigned int op);
 int blk_status_to_errno(blk_status_t status);
 blk_status_t errno_to_blk_status(int errno);
 
-int blk_poll(struct request_queue *q, blk_qc_t cookie, bool spin);
+/* only poll the hardware once, don't continue until a completion was found */
+#define BLK_POLL_ONESHOT		(1 << 0)
+/* do not sleep to wait for the expected completion time */
+#define BLK_POLL_NOSLEEP		(1 << 1)
+int blk_poll(struct request_queue *q, blk_qc_t cookie, unsigned int flags);
 
 static inline struct request_queue *bdev_get_queue(struct block_device *bdev)
 {
diff --git a/include/linux/fs.h b/include/linux/fs.h
index c3c88fdb9b2a..483fb557d92f 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -2026,7 +2026,7 @@ struct file_operations {
 	ssize_t (*write) (struct file *, const char __user *, size_t, loff_t *);
 	ssize_t (*read_iter) (struct kiocb *, struct iov_iter *);
 	ssize_t (*write_iter) (struct kiocb *, struct iov_iter *);
-	int (*iopoll)(struct kiocb *kiocb, bool spin);
+	int (*iopoll)(struct kiocb *kiocb, unsigned int flags);
 	int (*iterate) (struct file *, struct dir_context *);
 	int (*iterate_shared) (struct file *, struct dir_context *);
 	__poll_t (*poll) (struct file *, struct poll_table_struct *);
diff --git a/include/linux/iomap.h b/include/linux/iomap.h
index c87d0cb0de6d..56e5949ccb60 100644
--- a/include/linux/iomap.h
+++ b/include/linux/iomap.h
@@ -275,7 +275,7 @@ struct iomap_dio *__iomap_dio_rw(struct kiocb *iocb, struct iov_iter *iter,
 		const struct iomap_ops *ops, const struct iomap_dio_ops *dops,
 		unsigned int dio_flags);
 ssize_t iomap_dio_complete(struct iomap_dio *dio);
-int iomap_dio_iopoll(struct kiocb *kiocb, bool spin);
+int iomap_dio_iopoll(struct kiocb *kiocb, unsigned int flags);
 
 #ifdef CONFIG_SWAP
 struct file;
diff --git a/mm/page_io.c b/mm/page_io.c
index c493ce9ebcf5..5d5543fcefa4 100644
--- a/mm/page_io.c
+++ b/mm/page_io.c
@@ -428,7 +428,7 @@ int swap_readpage(struct page *page, bool synchronous)
 		if (!READ_ONCE(bio->bi_private))
 			break;
 
-		if (!blk_poll(disk->queue, qc, true))
+		if (!blk_poll(disk->queue, qc, 0))
 			blk_io_schedule();
 	}
 	__set_current_state(TASK_RUNNING);
-- 
2.30.2


^ permalink raw reply	[flat|nested] 40+ messages in thread

* [PATCH 09/15] block: rename REQ_HIPRI to REQ_POLLED
  2021-05-12 13:15 switch block layer polling to a bio based model v3 Christoph Hellwig
                   ` (7 preceding siblings ...)
  2021-05-12 13:15 ` [PATCH 08/15] io_uring: don't sleep when polling for I/O Christoph Hellwig
@ 2021-05-12 13:15 ` Christoph Hellwig
  2021-05-12 21:56   ` Sagi Grimberg
  2021-05-12 22:43   ` Chaitanya Kulkarni
  2021-05-12 13:15 ` [PATCH 10/15] block: use SLAB_TYPESAFE_BY_RCU for the bio slab Christoph Hellwig
                   ` (6 subsequent siblings)
  15 siblings, 2 replies; 40+ messages in thread
From: Christoph Hellwig @ 2021-05-12 13:15 UTC (permalink / raw)
  To: Jens Axboe
  Cc: Jeffle Xu, Ming Lei, Damien Le Moal, Keith Busch, Sagi Grimberg,
	Wunderlich, Mark, Vasudevan, Anil, linux-block, linux-fsdevel,
	linux-nvme

Unlike the RWF_HIPRI userspace ABI which is intentionally kept vague,
the bio flag is specific to the polling implementation, so rename and
document it properly.

Signed-off-by: Christoph Hellwig <hch@lst.de>
---
 block/blk-core.c          |  2 +-
 block/blk-merge.c         |  2 +-
 block/blk-mq-debugfs.c    |  2 +-
 block/blk-mq.c            |  4 ++--
 block/blk-mq.h            |  4 ++--
 drivers/nvme/host/core.c  |  2 +-
 drivers/scsi/scsi_debug.c | 10 +++++-----
 include/linux/bio.h       |  2 +-
 include/linux/blk_types.h |  4 ++--
 mm/page_io.c              |  2 +-
 10 files changed, 17 insertions(+), 17 deletions(-)

diff --git a/block/blk-core.c b/block/blk-core.c
index 689aac2625d2..94a817532472 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -837,7 +837,7 @@ static noinline_for_stack bool submit_bio_checks(struct bio *bio)
 	}
 
 	if (!test_bit(QUEUE_FLAG_POLL, &q->queue_flags))
-		bio->bi_opf &= ~REQ_HIPRI;
+		bio->bi_opf &= ~REQ_POLLED;
 
 	switch (bio_op(bio)) {
 	case REQ_OP_DISCARD:
diff --git a/block/blk-merge.c b/block/blk-merge.c
index 4d97fb6dd226..5c9d2a4ece86 100644
--- a/block/blk-merge.c
+++ b/block/blk-merge.c
@@ -285,7 +285,7 @@ static struct bio *blk_bio_segment_split(struct request_queue *q,
 	 * iopoll in direct IO routine. Given performance gain of iopoll for
 	 * big IO can be trival, disable iopoll when split needed.
 	 */
-	bio->bi_opf &= ~REQ_HIPRI;
+	bio->bi_opf &= ~REQ_POLLED;
 
 	return bio_split(bio, sectors, GFP_NOIO, bs);
 }
diff --git a/block/blk-mq-debugfs.c b/block/blk-mq-debugfs.c
index 2a75bc7401df..0b821b369ffd 100644
--- a/block/blk-mq-debugfs.c
+++ b/block/blk-mq-debugfs.c
@@ -286,7 +286,7 @@ static const char *const cmd_flag_name[] = {
 	CMD_FLAG_NAME(BACKGROUND),
 	CMD_FLAG_NAME(NOWAIT),
 	CMD_FLAG_NAME(NOUNMAP),
-	CMD_FLAG_NAME(HIPRI),
+	CMD_FLAG_NAME(POLLED),
 };
 #undef CMD_FLAG_NAME
 
diff --git a/block/blk-mq.c b/block/blk-mq.c
index 164e39d34bf6..b0b35473f339 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -667,7 +667,7 @@ bool blk_mq_complete_request_remote(struct request *rq)
 	 * For a polled request, always complete locallly, it's pointless
 	 * to redirect the completion.
 	 */
-	if (rq->cmd_flags & REQ_HIPRI)
+	if (rq->cmd_flags & REQ_POLLED)
 		return false;
 
 	if (blk_mq_complete_need_ipi(rq)) {
@@ -2216,7 +2216,7 @@ blk_qc_t blk_mq_submit_bio(struct bio *bio)
 
 	rq_qos_throttle(q, bio);
 
-	hipri = bio->bi_opf & REQ_HIPRI;
+	hipri = bio->bi_opf & REQ_POLLED;
 
 	data.cmd_flags = bio->bi_opf;
 	rq = __blk_mq_alloc_request(&data);
diff --git a/block/blk-mq.h b/block/blk-mq.h
index 9ce64bc4a6c8..2c1c73e19c89 100644
--- a/block/blk-mq.h
+++ b/block/blk-mq.h
@@ -108,9 +108,9 @@ static inline struct blk_mq_hw_ctx *blk_mq_map_queue(struct request_queue *q,
 	enum hctx_type type = HCTX_TYPE_DEFAULT;
 
 	/*
-	 * The caller ensure that if REQ_HIPRI, poll must be enabled.
+	 * The caller ensure that if REQ_POLLED, poll must be enabled.
 	 */
-	if (flags & REQ_HIPRI)
+	if (flags & REQ_POLLED)
 		type = HCTX_TYPE_POLL;
 	else if ((flags & REQ_OP_MASK) == REQ_OP_READ)
 		type = HCTX_TYPE_READ;
diff --git a/drivers/nvme/host/core.c b/drivers/nvme/host/core.c
index 8fa7e90020b0..c58dde3460e9 100644
--- a/drivers/nvme/host/core.c
+++ b/drivers/nvme/host/core.c
@@ -1027,7 +1027,7 @@ static void nvme_execute_rq_polled(struct request_queue *q,
 
 	WARN_ON_ONCE(!test_bit(QUEUE_FLAG_POLL, &q->queue_flags));
 
-	rq->cmd_flags |= REQ_HIPRI;
+	rq->cmd_flags |= REQ_POLLED;
 	rq->end_io_data = &wait;
 	blk_execute_rq_nowait(bd_disk, rq, at_head, nvme_end_sync_rq);
 
diff --git a/drivers/scsi/scsi_debug.c b/drivers/scsi/scsi_debug.c
index a5d1633b5bd8..81384d28ff90 100644
--- a/drivers/scsi/scsi_debug.c
+++ b/drivers/scsi/scsi_debug.c
@@ -5367,7 +5367,7 @@ static int schedule_resp(struct scsi_cmnd *cmnd, struct sdebug_dev_info *devip,
 {
 	bool new_sd_dp;
 	bool inject = false;
-	bool hipri = (cmnd->request->cmd_flags & REQ_HIPRI);
+	bool polled = (cmnd->request->cmd_flags & REQ_POLLED);
 	int k, num_in_q, qdepth;
 	unsigned long iflags;
 	u64 ns_from_boot = 0;
@@ -5454,7 +5454,7 @@ static int schedule_resp(struct scsi_cmnd *cmnd, struct sdebug_dev_info *devip,
 	if (sdebug_host_max_queue)
 		sd_dp->hc_idx = get_tag(cmnd);
 
-	if (hipri)
+	if (polled)
 		ns_from_boot = ktime_get_boottime_ns();
 
 	/* one of the resp_*() response functions is called here */
@@ -5514,7 +5514,7 @@ static int schedule_resp(struct scsi_cmnd *cmnd, struct sdebug_dev_info *devip,
 				kt -= d;
 			}
 		}
-		if (hipri) {
+		if (polled) {
 			sd_dp->cmpl_ts = ktime_add(ns_to_ktime(ns_from_boot), kt);
 			spin_lock_irqsave(&sqp->qc_lock, iflags);
 			if (!sd_dp->init_poll) {
@@ -5545,7 +5545,7 @@ static int schedule_resp(struct scsi_cmnd *cmnd, struct sdebug_dev_info *devip,
 		if (unlikely((sdebug_opts & SDEBUG_OPT_CMD_ABORT) &&
 			     atomic_read(&sdeb_inject_pending)))
 			sd_dp->aborted = true;
-		if (hipri) {
+		if (polled) {
 			sd_dp->cmpl_ts = ns_to_ktime(ns_from_boot);
 			spin_lock_irqsave(&sqp->qc_lock, iflags);
 			if (!sd_dp->init_poll) {
@@ -7313,7 +7313,7 @@ static int sdebug_blk_mq_poll(struct Scsi_Host *shost, unsigned int queue_num)
 			if (kt_from_boot < sd_dp->cmpl_ts)
 				continue;
 
-		} else		/* ignoring non REQ_HIPRI requests */
+		} else		/* ignoring non REQ_POLLED requests */
 			continue;
 		devip = (struct sdebug_dev_info *)scp->device->hostdata;
 		if (likely(devip))
diff --git a/include/linux/bio.h b/include/linux/bio.h
index a0b4cfdf62a4..439a70bc42e2 100644
--- a/include/linux/bio.h
+++ b/include/linux/bio.h
@@ -817,7 +817,7 @@ static inline int bio_integrity_add_page(struct bio *bio, struct page *page,
  */
 static inline void bio_set_polled(struct bio *bio, struct kiocb *kiocb)
 {
-	bio->bi_opf |= REQ_HIPRI;
+	bio->bi_opf |= REQ_POLLED;
 	if (!is_sync_kiocb(kiocb))
 		bio->bi_opf |= REQ_NOWAIT;
 }
diff --git a/include/linux/blk_types.h b/include/linux/blk_types.h
index d0cf835d3b50..ac60432752e3 100644
--- a/include/linux/blk_types.h
+++ b/include/linux/blk_types.h
@@ -392,7 +392,7 @@ enum req_flag_bits {
 	/* command specific flags for REQ_OP_WRITE_ZEROES: */
 	__REQ_NOUNMAP,		/* do not free blocks when zeroing */
 
-	__REQ_HIPRI,
+	__REQ_POLLED,		/* caller polls for completion using blk_poll */
 
 	/* for driver use */
 	__REQ_DRV,
@@ -417,7 +417,7 @@ enum req_flag_bits {
 #define REQ_CGROUP_PUNT		(1ULL << __REQ_CGROUP_PUNT)
 
 #define REQ_NOUNMAP		(1ULL << __REQ_NOUNMAP)
-#define REQ_HIPRI		(1ULL << __REQ_HIPRI)
+#define REQ_POLLED		(1ULL << __REQ_POLLED)
 
 #define REQ_DRV			(1ULL << __REQ_DRV)
 #define REQ_SWAP		(1ULL << __REQ_SWAP)
diff --git a/mm/page_io.c b/mm/page_io.c
index 5d5543fcefa4..ed2eded74f3a 100644
--- a/mm/page_io.c
+++ b/mm/page_io.c
@@ -416,7 +416,7 @@ int swap_readpage(struct page *page, bool synchronous)
 	 * attempt to access it in the page fault retry time check.
 	 */
 	if (synchronous) {
-		bio->bi_opf |= REQ_HIPRI;
+		bio->bi_opf |= REQ_POLLED;
 		get_task_struct(current);
 		bio->bi_private = current;
 	}
-- 
2.30.2


^ permalink raw reply	[flat|nested] 40+ messages in thread

* [PATCH 10/15] block: use SLAB_TYPESAFE_BY_RCU for the bio slab
  2021-05-12 13:15 switch block layer polling to a bio based model v3 Christoph Hellwig
                   ` (8 preceding siblings ...)
  2021-05-12 13:15 ` [PATCH 09/15] block: rename REQ_HIPRI to REQ_POLLED Christoph Hellwig
@ 2021-05-12 13:15 ` Christoph Hellwig
  2021-05-12 13:15 ` [PATCH 11/15] block: define 'struct bvec_iter' as packed Christoph Hellwig
                   ` (5 subsequent siblings)
  15 siblings, 0 replies; 40+ messages in thread
From: Christoph Hellwig @ 2021-05-12 13:15 UTC (permalink / raw)
  To: Jens Axboe
  Cc: Jeffle Xu, Ming Lei, Damien Le Moal, Keith Busch, Sagi Grimberg,
	Wunderlich, Mark, Vasudevan, Anil, linux-block, linux-fsdevel,
	linux-nvme

This flags ensures that the pages will not be reused for non-bio
allocations before the end of an RCU grace period.  With that we can
safely use a RCU lookup for bio polling as long as we are fine with
occasionally polling the wrong device.

Signed-off-by: Christoph Hellwig <hch@lst.de>
---
 block/bio.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/block/bio.c b/block/bio.c
index 44205dfb6b60..de5505d7018e 100644
--- a/block/bio.c
+++ b/block/bio.c
@@ -82,7 +82,8 @@ static struct bio_slab *create_bio_slab(unsigned int size)
 
 	snprintf(bslab->name, sizeof(bslab->name), "bio-%d", size);
 	bslab->slab = kmem_cache_create(bslab->name, size,
-			ARCH_KMALLOC_MINALIGN, SLAB_HWCACHE_ALIGN, NULL);
+			ARCH_KMALLOC_MINALIGN,
+			SLAB_HWCACHE_ALIGN | SLAB_TYPESAFE_BY_RCU, NULL);
 	if (!bslab->slab)
 		goto fail_alloc_slab;
 
-- 
2.30.2


^ permalink raw reply	[flat|nested] 40+ messages in thread

* [PATCH 11/15] block: define 'struct bvec_iter' as packed
  2021-05-12 13:15 switch block layer polling to a bio based model v3 Christoph Hellwig
                   ` (9 preceding siblings ...)
  2021-05-12 13:15 ` [PATCH 10/15] block: use SLAB_TYPESAFE_BY_RCU for the bio slab Christoph Hellwig
@ 2021-05-12 13:15 ` Christoph Hellwig
  2021-05-12 21:58   ` Sagi Grimberg
  2021-05-12 13:15 ` [PATCH 12/15] block: switch polling to be bio based Christoph Hellwig
                   ` (4 subsequent siblings)
  15 siblings, 1 reply; 40+ messages in thread
From: Christoph Hellwig @ 2021-05-12 13:15 UTC (permalink / raw)
  To: Jens Axboe
  Cc: Jeffle Xu, Ming Lei, Damien Le Moal, Keith Busch, Sagi Grimberg,
	Wunderlich, Mark, Vasudevan, Anil, linux-block, linux-fsdevel,
	linux-nvme, Hannes Reinecke

From: Ming Lei <ming.lei@redhat.com>

'struct bvec_iter' is embedded into 'struct bio', define it as packed
so that we can get one extra 4bytes for other uses without expanding
bio.

'struct bvec_iter' is often allocated on stack, so making it packed
doesn't affect performance. Also I have run io_uring on both
nvme/null_blk, and not observe performance effect in this way.

Suggested-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Ming Lei <ming.lei@redhat.com>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Signed-off-by: Christoph Hellwig <hch@lst.de>
---
 include/linux/bvec.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/linux/bvec.h b/include/linux/bvec.h
index ff832e698efb..a0c4f41dfc83 100644
--- a/include/linux/bvec.h
+++ b/include/linux/bvec.h
@@ -43,7 +43,7 @@ struct bvec_iter {
 
 	unsigned int            bi_bvec_done;	/* number of bytes completed in
 						   current bvec */
-};
+} __packed;
 
 struct bvec_iter_all {
 	struct bio_vec	bv;
-- 
2.30.2


^ permalink raw reply	[flat|nested] 40+ messages in thread

* [PATCH 12/15] block: switch polling to be bio based
  2021-05-12 13:15 switch block layer polling to a bio based model v3 Christoph Hellwig
                   ` (10 preceding siblings ...)
  2021-05-12 13:15 ` [PATCH 11/15] block: define 'struct bvec_iter' as packed Christoph Hellwig
@ 2021-05-12 13:15 ` Christoph Hellwig
  2021-05-12 22:03   ` Sagi Grimberg
  2021-05-13  1:23   ` Ming Lei
  2021-05-12 13:15 ` [PATCH 13/15] block: don't allow writing to the poll queue attribute Christoph Hellwig
                   ` (3 subsequent siblings)
  15 siblings, 2 replies; 40+ messages in thread
From: Christoph Hellwig @ 2021-05-12 13:15 UTC (permalink / raw)
  To: Jens Axboe
  Cc: Jeffle Xu, Ming Lei, Damien Le Moal, Keith Busch, Sagi Grimberg,
	Wunderlich, Mark, Vasudevan, Anil, linux-block, linux-fsdevel,
	linux-nvme

Replace the blk_poll interface that requires the caller to keep a queue
and cookie from the submissions with polling based on the bio.

Polling for the bio itself leads to a few advantages:

 - the cookie construction can made entirely private in blk-mq.c
 - the caller does not need to remember the request_queue and cookie
   separately and thus sidesteps their lifetime issues
 - keeping the device and the cookie inside the bio allows to trivially
   support polling BIOs remapping by stacking drivers
 - a lot of code to propagate the cookie back up the submission path can
   be removed entirely.

Signed-off-by: Christoph Hellwig <hch@lst.de>
---
 arch/m68k/emu/nfblock.c             |   3 +-
 arch/xtensa/platforms/iss/simdisk.c |   3 +-
 block/bio.c                         |   1 +
 block/blk-core.c                    | 120 +++++++++++++++++++++-------
 block/blk-mq.c                      |  73 ++++++-----------
 block/blk-mq.h                      |   2 +
 drivers/block/brd.c                 |  12 ++-
 drivers/block/drbd/drbd_int.h       |   2 +-
 drivers/block/drbd/drbd_req.c       |   3 +-
 drivers/block/n64cart.c             |  12 ++-
 drivers/block/null_blk/main.c       |   3 +-
 drivers/block/pktcdvd.c             |   7 +-
 drivers/block/ps3vram.c             |   6 +-
 drivers/block/rsxx/dev.c            |   7 +-
 drivers/block/zram/zram_drv.c       |  10 +--
 drivers/lightnvm/pblk-init.c        |   6 +-
 drivers/md/bcache/request.c         |  13 ++-
 drivers/md/bcache/request.h         |   4 +-
 drivers/md/dm.c                     |  28 +++----
 drivers/md/md.c                     |  10 +--
 drivers/nvdimm/blk.c                |   5 +-
 drivers/nvdimm/btt.c                |   5 +-
 drivers/nvdimm/pmem.c               |   3 +-
 drivers/nvme/host/core.c            |   2 +-
 drivers/nvme/host/multipath.c       |   6 +-
 drivers/s390/block/dcssblk.c        |   7 +-
 drivers/s390/block/xpram.c          |   5 +-
 fs/block_dev.c                      |  25 ++----
 fs/btrfs/inode.c                    |   8 +-
 fs/ext4/file.c                      |   2 +-
 fs/gfs2/file.c                      |   4 +-
 fs/iomap/direct-io.c                |  39 +++------
 fs/xfs/xfs_file.c                   |   2 +-
 fs/zonefs/super.c                   |   2 +-
 include/linux/bio.h                 |   2 +-
 include/linux/blk-mq.h              |  15 +---
 include/linux/blk_types.h           |  12 ++-
 include/linux/blkdev.h              |   8 +-
 include/linux/fs.h                  |   6 +-
 include/linux/iomap.h               |   3 +-
 mm/page_io.c                        |   8 +-
 41 files changed, 223 insertions(+), 271 deletions(-)

diff --git a/arch/m68k/emu/nfblock.c b/arch/m68k/emu/nfblock.c
index ba808543161a..dd36808f0d5e 100644
--- a/arch/m68k/emu/nfblock.c
+++ b/arch/m68k/emu/nfblock.c
@@ -59,7 +59,7 @@ struct nfhd_device {
 	struct gendisk *disk;
 };
 
-static blk_qc_t nfhd_submit_bio(struct bio *bio)
+static void nfhd_submit_bio(struct bio *bio)
 {
 	struct nfhd_device *dev = bio->bi_bdev->bd_disk->private_data;
 	struct bio_vec bvec;
@@ -77,7 +77,6 @@ static blk_qc_t nfhd_submit_bio(struct bio *bio)
 		sec += len;
 	}
 	bio_endio(bio);
-	return BLK_QC_T_NONE;
 }
 
 static int nfhd_getgeo(struct block_device *bdev, struct hd_geometry *geo)
diff --git a/arch/xtensa/platforms/iss/simdisk.c b/arch/xtensa/platforms/iss/simdisk.c
index fc09be7b1347..182825d639e2 100644
--- a/arch/xtensa/platforms/iss/simdisk.c
+++ b/arch/xtensa/platforms/iss/simdisk.c
@@ -101,7 +101,7 @@ static void simdisk_transfer(struct simdisk *dev, unsigned long sector,
 	spin_unlock(&dev->lock);
 }
 
-static blk_qc_t simdisk_submit_bio(struct bio *bio)
+static void simdisk_submit_bio(struct bio *bio)
 {
 	struct simdisk *dev = bio->bi_bdev->bd_disk->private_data;
 	struct bio_vec bvec;
@@ -119,7 +119,6 @@ static blk_qc_t simdisk_submit_bio(struct bio *bio)
 	}
 
 	bio_endio(bio);
-	return BLK_QC_T_NONE;
 }
 
 static int simdisk_open(struct block_device *bdev, fmode_t mode)
diff --git a/block/bio.c b/block/bio.c
index de5505d7018e..986908cc99d4 100644
--- a/block/bio.c
+++ b/block/bio.c
@@ -250,6 +250,7 @@ void bio_init(struct bio *bio, struct bio_vec *table,
 	memset(bio, 0, sizeof(*bio));
 	atomic_set(&bio->__bi_remaining, 1);
 	atomic_set(&bio->__bi_cnt, 1);
+	bio->bi_cookie = BLK_QC_T_NONE;
 
 	bio->bi_io_vec = table;
 	bio->bi_max_vecs = max_vecs;
diff --git a/block/blk-core.c b/block/blk-core.c
index 94a817532472..c024cba98195 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -910,18 +910,18 @@ static noinline_for_stack bool submit_bio_checks(struct bio *bio)
 	return false;
 }
 
-static blk_qc_t __submit_bio(struct bio *bio)
+static void __submit_bio(struct bio *bio)
 {
 	struct gendisk *disk = bio->bi_bdev->bd_disk;
-	blk_qc_t ret = BLK_QC_T_NONE;
 
 	if (blk_crypto_bio_prep(&bio)) {
-		if (!disk->fops->submit_bio)
-			return blk_mq_submit_bio(bio);
-		ret = disk->fops->submit_bio(bio);
+		if (!disk->fops->submit_bio) {
+			blk_mq_submit_bio(bio);
+			return;
+		}
+		disk->fops->submit_bio(bio);
 	}
 	blk_queue_exit(disk->queue);
-	return ret;
 }
 
 /*
@@ -943,10 +943,9 @@ static blk_qc_t __submit_bio(struct bio *bio)
  * bio_list_on_stack[1] contains bios that were submitted before the current
  *	->submit_bio_bio, but that haven't been processed yet.
  */
-static blk_qc_t __submit_bio_noacct(struct bio *bio)
+static void __submit_bio_noacct(struct bio *bio)
 {
 	struct bio_list bio_list_on_stack[2];
-	blk_qc_t ret = BLK_QC_T_NONE;
 
 	BUG_ON(bio->bi_next);
 
@@ -966,7 +965,7 @@ static blk_qc_t __submit_bio_noacct(struct bio *bio)
 		bio_list_on_stack[1] = bio_list_on_stack[0];
 		bio_list_init(&bio_list_on_stack[0]);
 
-		ret = __submit_bio(bio);
+		__submit_bio(bio);
 
 		/*
 		 * Sort new bios into those for a lower level and those for the
@@ -989,13 +988,11 @@ static blk_qc_t __submit_bio_noacct(struct bio *bio)
 	} while ((bio = bio_list_pop(&bio_list_on_stack[0])));
 
 	current->bio_list = NULL;
-	return ret;
 }
 
-static blk_qc_t __submit_bio_noacct_mq(struct bio *bio)
+static void __submit_bio_noacct_mq(struct bio *bio)
 {
 	struct bio_list bio_list[2] = { };
-	blk_qc_t ret = BLK_QC_T_NONE;
 
 	current->bio_list = bio_list;
 
@@ -1007,15 +1004,13 @@ static blk_qc_t __submit_bio_noacct_mq(struct bio *bio)
 
 		if (!blk_crypto_bio_prep(&bio)) {
 			blk_queue_exit(disk->queue);
-			ret = BLK_QC_T_NONE;
 			continue;
 		}
 
-		ret = blk_mq_submit_bio(bio);
+		blk_mq_submit_bio(bio);
 	} while ((bio = bio_list_pop(&bio_list[0])));
 
 	current->bio_list = NULL;
-	return ret;
 }
 
 /**
@@ -1027,10 +1022,10 @@ static blk_qc_t __submit_bio_noacct_mq(struct bio *bio)
  * systems and other upper level users of the block layer should use
  * submit_bio() instead.
  */
-blk_qc_t submit_bio_noacct(struct bio *bio)
+void submit_bio_noacct(struct bio *bio)
 {
 	if (!submit_bio_checks(bio))
-		return BLK_QC_T_NONE;
+		return;
 
 	/*
 	 * We only want one ->submit_bio to be active at a time, else stack
@@ -1038,14 +1033,12 @@ blk_qc_t submit_bio_noacct(struct bio *bio)
 	 * to collect a list of requests submited by a ->submit_bio method while
 	 * it is active, and then process them after it returned.
 	 */
-	if (current->bio_list) {
+	if (current->bio_list)
 		bio_list_add(&current->bio_list[0], bio);
-		return BLK_QC_T_NONE;
-	}
-
-	if (!bio->bi_bdev->bd_disk->fops->submit_bio)
-		return __submit_bio_noacct_mq(bio);
-	return __submit_bio_noacct(bio);
+	else if (!bio->bi_bdev->bd_disk->fops->submit_bio)
+		__submit_bio_noacct_mq(bio);
+	else
+		__submit_bio_noacct(bio);
 }
 EXPORT_SYMBOL(submit_bio_noacct);
 
@@ -1062,10 +1055,10 @@ EXPORT_SYMBOL(submit_bio_noacct);
  * in @bio.  The bio must NOT be touched by thecaller until ->bi_end_io() has
  * been called.
  */
-blk_qc_t submit_bio(struct bio *bio)
+void submit_bio(struct bio *bio)
 {
 	if (blkcg_punt_bio_submit(bio))
-		return BLK_QC_T_NONE;
+		return;
 
 	/*
 	 * If it's a regular read/write or a barrier with data attached,
@@ -1097,19 +1090,84 @@ blk_qc_t submit_bio(struct bio *bio)
 	if (unlikely(bio_op(bio) == REQ_OP_READ &&
 	    bio_flagged(bio, BIO_WORKINGSET))) {
 		unsigned long pflags;
-		blk_qc_t ret;
 
 		psi_memstall_enter(&pflags);
-		ret = submit_bio_noacct(bio);
+		submit_bio_noacct(bio);
 		psi_memstall_leave(&pflags);
-
-		return ret;
+		return;
 	}
 
-	return submit_bio_noacct(bio);
+	submit_bio_noacct(bio);
 }
 EXPORT_SYMBOL(submit_bio);
 
+/**
+ * bio_poll - poll for BIO completions
+ * @bio: bio to poll for
+ * @flags: BLK_POLL_* flags that control the behavior
+ *
+ * Poll for completions on queue associated with the bio. Returns number of
+ * completed entries found.
+ *
+ * Note: the caller must either be the context that submitted @bio, or
+ * be in a RCU critical section to prevent freeing of @bio.
+ */
+int bio_poll(struct bio *bio, unsigned int flags)
+{
+	struct request_queue *q = bio->bi_bdev->bd_disk->queue;
+	blk_qc_t cookie = READ_ONCE(bio->bi_cookie);
+
+	if (cookie == BLK_QC_T_NONE ||
+	    !test_bit(QUEUE_FLAG_POLL, &q->queue_flags))
+		return 0;
+
+	if (current->plug)
+		blk_flush_plug_list(current->plug, false);
+
+	/* not yet implemented, so this should not happen */
+	if (WARN_ON_ONCE(!queue_is_mq(q)))
+		return 0;
+	return blk_mq_poll(q, cookie, flags);
+}
+EXPORT_SYMBOL_GPL(bio_poll);
+
+/*
+ * Helper to implement file_operations.iopoll.  Requires the bio to be stored
+ * in iocb->private, and cleared before freeing the bio.
+ */
+int iocb_bio_iopoll(struct kiocb *kiocb, unsigned int flags)
+{
+	struct bio *bio;
+	int ret = 0;
+
+	/*
+	 * Note: the bio cache only uses SLAB_TYPESAFE_BY_RCU, so bio can
+	 * point to a freshly allocated bio at this point.  If that happens
+	 * we have a few cases to consider:
+	 *
+	 *  1) the bio is beeing initialized and bi_bdev is NULL.  We can just
+	 *     simply nothing in this case
+	 *  2) the bio points to a not poll enabled device.  bio_poll will catch
+	 *     this and return 0
+	 *  3) the bio points to a poll capable device, including but not
+	 *     limited to the one that the original bio pointed to.  In this
+	 *     case we will call into the actual poll method and poll for I/O,
+	 *     even if we don't need to, but it won't cause harm either.
+	 *
+	 * For cases 2) and 3) above the RCU grace period ensures that the
+	 * bi_bdev is still allocated, and because partitions hold a reference
+	 * to the whole device bdev and thus disk it is still valid.
+	 */
+	rcu_read_lock();
+	bio = READ_ONCE(kiocb->private);
+	if (bio && bio->bi_bdev)
+		ret = bio_poll(bio, flags);
+	rcu_read_unlock();
+
+	return ret;
+}
+EXPORT_SYMBOL_GPL(iocb_bio_iopoll);
+
 /**
  * blk_cloned_rq_check_limits - Helper function to check a cloned request
  *                              for the new queue limits
diff --git a/block/blk-mq.c b/block/blk-mq.c
index b0b35473f339..9769a351f81b 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -63,6 +63,9 @@ static int blk_mq_poll_stats_bkt(const struct request *rq)
 	return bucket;
 }
 
+#define BLK_QC_T_SHIFT		16
+#define BLK_QC_T_INTERNAL	(1U << 31)
+
 static inline struct blk_mq_hw_ctx *blk_qc_to_hctx(struct request_queue *q,
 		blk_qc_t qc)
 {
@@ -79,6 +82,13 @@ static inline struct request *blk_qc_to_rq(struct blk_mq_hw_ctx *hctx,
 	return blk_mq_tag_to_rq(hctx->tags, tag);
 }
 
+static inline blk_qc_t blk_rq_to_qc(struct request *rq)
+{
+	return (rq->mq_hctx->queue_num << BLK_QC_T_SHIFT) |
+		(rq->tag != -1 ?
+		 rq->tag : (rq->internal_tag | BLK_QC_T_INTERNAL));
+}
+
 /*
  * Check if any of the ctx, dispatch list or elevator
  * have pending work in this hardware queue.
@@ -747,6 +757,8 @@ void blk_mq_start_request(struct request *rq)
 	if (blk_integrity_rq(rq) && req_op(rq) == REQ_OP_WRITE)
 		q->integrity.profile->prepare_fn(rq);
 #endif
+	if (rq->bio && rq->bio->bi_opf & REQ_POLLED)
+	        WRITE_ONCE(rq->bio->bi_cookie, blk_rq_to_qc(rq));
 }
 EXPORT_SYMBOL(blk_mq_start_request);
 
@@ -1992,19 +2004,15 @@ static void blk_mq_bio_to_request(struct request *rq, struct bio *bio,
 }
 
 static blk_status_t __blk_mq_issue_directly(struct blk_mq_hw_ctx *hctx,
-					    struct request *rq,
-					    blk_qc_t *cookie, bool last)
+					    struct request *rq, bool last)
 {
 	struct request_queue *q = rq->q;
 	struct blk_mq_queue_data bd = {
 		.rq = rq,
 		.last = last,
 	};
-	blk_qc_t new_cookie;
 	blk_status_t ret;
 
-	new_cookie = request_to_qc_t(hctx, rq);
-
 	/*
 	 * For OK queue, we are done. For error, caller may kill it.
 	 * Any other error (busy), just add it to our list as we
@@ -2014,7 +2022,6 @@ static blk_status_t __blk_mq_issue_directly(struct blk_mq_hw_ctx *hctx,
 	switch (ret) {
 	case BLK_STS_OK:
 		blk_mq_update_dispatch_busy(hctx, false);
-		*cookie = new_cookie;
 		break;
 	case BLK_STS_RESOURCE:
 	case BLK_STS_DEV_RESOURCE:
@@ -2023,7 +2030,6 @@ static blk_status_t __blk_mq_issue_directly(struct blk_mq_hw_ctx *hctx,
 		break;
 	default:
 		blk_mq_update_dispatch_busy(hctx, false);
-		*cookie = BLK_QC_T_NONE;
 		break;
 	}
 
@@ -2032,7 +2038,6 @@ static blk_status_t __blk_mq_issue_directly(struct blk_mq_hw_ctx *hctx,
 
 static blk_status_t __blk_mq_try_issue_directly(struct blk_mq_hw_ctx *hctx,
 						struct request *rq,
-						blk_qc_t *cookie,
 						bool bypass_insert, bool last)
 {
 	struct request_queue *q = rq->q;
@@ -2066,7 +2071,7 @@ static blk_status_t __blk_mq_try_issue_directly(struct blk_mq_hw_ctx *hctx,
 		goto insert;
 	}
 
-	return __blk_mq_issue_directly(hctx, rq, cookie, last);
+	return __blk_mq_issue_directly(hctx, rq, last);
 insert:
 	if (bypass_insert)
 		return BLK_STS_RESOURCE;
@@ -2080,7 +2085,6 @@ static blk_status_t __blk_mq_try_issue_directly(struct blk_mq_hw_ctx *hctx,
  * blk_mq_try_issue_directly - Try to send a request directly to device driver.
  * @hctx: Pointer of the associated hardware queue.
  * @rq: Pointer to request to be sent.
- * @cookie: Request queue cookie.
  *
  * If the device has enough resources to accept a new request now, send the
  * request directly to device driver. Else, insert at hctx->dispatch queue, so
@@ -2088,7 +2092,7 @@ static blk_status_t __blk_mq_try_issue_directly(struct blk_mq_hw_ctx *hctx,
  * queue have higher priority.
  */
 static void blk_mq_try_issue_directly(struct blk_mq_hw_ctx *hctx,
-		struct request *rq, blk_qc_t *cookie)
+		struct request *rq)
 {
 	blk_status_t ret;
 	int srcu_idx;
@@ -2097,7 +2101,7 @@ static void blk_mq_try_issue_directly(struct blk_mq_hw_ctx *hctx,
 
 	hctx_lock(hctx, &srcu_idx);
 
-	ret = __blk_mq_try_issue_directly(hctx, rq, cookie, false, true);
+	ret = __blk_mq_try_issue_directly(hctx, rq, false, true);
 	if (ret == BLK_STS_RESOURCE || ret == BLK_STS_DEV_RESOURCE)
 		blk_mq_request_bypass_insert(rq, false, true);
 	else if (ret != BLK_STS_OK)
@@ -2110,11 +2114,10 @@ blk_status_t blk_mq_request_issue_directly(struct request *rq, bool last)
 {
 	blk_status_t ret;
 	int srcu_idx;
-	blk_qc_t unused_cookie;
 	struct blk_mq_hw_ctx *hctx = rq->mq_hctx;
 
 	hctx_lock(hctx, &srcu_idx);
-	ret = __blk_mq_try_issue_directly(hctx, rq, &unused_cookie, true, last);
+	ret = __blk_mq_try_issue_directly(hctx, rq, true, last);
 	hctx_unlock(hctx, srcu_idx);
 
 	return ret;
@@ -2182,10 +2185,8 @@ static void blk_add_rq_to_plug(struct blk_plug *plug, struct request *rq)
  *
  * It will not queue the request if there is an error with the bio, or at the
  * request creation.
- *
- * Returns: Request queue cookie.
  */
-blk_qc_t blk_mq_submit_bio(struct bio *bio)
+void blk_mq_submit_bio(struct bio *bio)
 {
 	struct request_queue *q = bio->bi_bdev->bd_disk->queue;
 	const int is_sync = op_is_sync(bio->bi_opf);
@@ -2197,9 +2198,7 @@ blk_qc_t blk_mq_submit_bio(struct bio *bio)
 	struct blk_plug *plug;
 	struct request *same_queue_rq = NULL;
 	unsigned int nr_segs;
-	blk_qc_t cookie;
 	blk_status_t ret;
-	bool hipri;
 
 	blk_queue_bounce(q, &bio);
 	__blk_queue_split(&bio, &nr_segs);
@@ -2216,8 +2215,6 @@ blk_qc_t blk_mq_submit_bio(struct bio *bio)
 
 	rq_qos_throttle(q, bio);
 
-	hipri = bio->bi_opf & REQ_POLLED;
-
 	data.cmd_flags = bio->bi_opf;
 	rq = __blk_mq_alloc_request(&data);
 	if (unlikely(!rq)) {
@@ -2231,8 +2228,6 @@ blk_qc_t blk_mq_submit_bio(struct bio *bio)
 
 	rq_qos_track(q, rq, bio);
 
-	cookie = request_to_qc_t(data.hctx, rq);
-
 	blk_mq_bio_to_request(rq, bio, nr_segs);
 
 	ret = blk_crypto_init_request(rq);
@@ -2240,7 +2235,7 @@ blk_qc_t blk_mq_submit_bio(struct bio *bio)
 		bio->bi_status = ret;
 		bio_endio(bio);
 		blk_mq_free_request(rq);
-		return BLK_QC_T_NONE;
+		return;
 	}
 
 	plug = blk_mq_plug(q, bio);
@@ -2295,8 +2290,7 @@ blk_qc_t blk_mq_submit_bio(struct bio *bio)
 		if (same_queue_rq) {
 			data.hctx = same_queue_rq->mq_hctx;
 			trace_block_unplug(q, 1, true);
-			blk_mq_try_issue_directly(data.hctx, same_queue_rq,
-					&cookie);
+			blk_mq_try_issue_directly(data.hctx, same_queue_rq);
 		}
 	} else if ((q->nr_hw_queues > 1 && is_sync) ||
 			!data.hctx->dispatch_busy) {
@@ -2304,18 +2298,15 @@ blk_qc_t blk_mq_submit_bio(struct bio *bio)
 		 * There is no scheduler and we can try to send directly
 		 * to the hardware.
 		 */
-		blk_mq_try_issue_directly(data.hctx, rq, &cookie);
+		blk_mq_try_issue_directly(data.hctx, rq);
 	} else {
 		/* Default case. */
 		blk_mq_sched_insert_request(rq, false, true, true);
 	}
 
-	if (!hipri)
-		return BLK_QC_T_NONE;
-	return cookie;
+	return;
 queue_exit:
 	blk_queue_exit(q);
-	return BLK_QC_T_NONE;
 }
 
 void blk_mq_free_rqs(struct blk_mq_tag_set *set, struct blk_mq_tags *tags,
@@ -3905,25 +3896,8 @@ static int blk_mq_poll_classic(struct request_queue *q, blk_qc_t cookie,
 	return 0;
 }
 
-/**
- * blk_poll - poll for IO completions
- * @q:  the queue
- * @cookie: cookie passed back at IO submission time
- * @flags: BLK_POLL_* flags that control the behavior
- *
- * Description:
- *    Poll for completions on the passed in queue. Returns number of
- *    completed entries found.
- */
-int blk_poll(struct request_queue *q, blk_qc_t cookie, unsigned int flags)
+int blk_mq_poll(struct request_queue *q, blk_qc_t cookie, unsigned int flags)
 {
-	if (cookie == BLK_QC_T_NONE ||
-	    !test_bit(QUEUE_FLAG_POLL, &q->queue_flags))
-		return 0;
-
-	if (current->plug)
-		blk_flush_plug_list(current->plug, false);
-
 	if (!(flags & BLK_POLL_NOSLEEP) &&
 	    q->poll_nsec != BLK_MQ_POLL_CLASSIC) {
 		if (blk_mq_poll_hybrid(q, cookie))
@@ -3931,7 +3905,6 @@ int blk_poll(struct request_queue *q, blk_qc_t cookie, unsigned int flags)
 	}
 	return blk_mq_poll_classic(q, cookie, flags);
 }
-EXPORT_SYMBOL_GPL(blk_poll);
 
 unsigned int blk_mq_rq_cpu(struct request *rq)
 {
diff --git a/block/blk-mq.h b/block/blk-mq.h
index 2c1c73e19c89..f7a0a9489e61 100644
--- a/block/blk-mq.h
+++ b/block/blk-mq.h
@@ -37,6 +37,8 @@ struct blk_mq_ctx {
 	struct kobject		kobj;
 } ____cacheline_aligned_in_smp;
 
+void blk_mq_submit_bio(struct bio *bio);
+int blk_mq_poll(struct request_queue *q, blk_qc_t cookie, unsigned int flags);
 void blk_mq_exit_queue(struct request_queue *q);
 int blk_mq_update_nr_requests(struct request_queue *q, unsigned int nr);
 void blk_mq_wake_waiters(struct request_queue *q);
diff --git a/drivers/block/brd.c b/drivers/block/brd.c
index 7562cf30b14e..7c69ed3765c1 100644
--- a/drivers/block/brd.c
+++ b/drivers/block/brd.c
@@ -287,7 +287,7 @@ static int brd_do_bvec(struct brd_device *brd, struct page *page,
 	return err;
 }
 
-static blk_qc_t brd_submit_bio(struct bio *bio)
+static void brd_submit_bio(struct bio *bio)
 {
 	struct brd_device *brd = bio->bi_bdev->bd_disk->private_data;
 	sector_t sector = bio->bi_iter.bi_sector;
@@ -304,16 +304,14 @@ static blk_qc_t brd_submit_bio(struct bio *bio)
 
 		err = brd_do_bvec(brd, bvec.bv_page, len, bvec.bv_offset,
 				  bio_op(bio), sector);
-		if (err)
-			goto io_error;
+		if (err) {
+			bio_io_error(bio);
+			return;
+		}
 		sector += len >> SECTOR_SHIFT;
 	}
 
 	bio_endio(bio);
-	return BLK_QC_T_NONE;
-io_error:
-	bio_io_error(bio);
-	return BLK_QC_T_NONE;
 }
 
 static int brd_rw_page(struct block_device *bdev, sector_t sector,
diff --git a/drivers/block/drbd/drbd_int.h b/drivers/block/drbd/drbd_int.h
index 5d9181382ce1..6674a0b88341 100644
--- a/drivers/block/drbd/drbd_int.h
+++ b/drivers/block/drbd/drbd_int.h
@@ -1448,7 +1448,7 @@ extern void conn_free_crypto(struct drbd_connection *connection);
 /* drbd_req */
 extern void do_submit(struct work_struct *ws);
 extern void __drbd_make_request(struct drbd_device *, struct bio *);
-extern blk_qc_t drbd_submit_bio(struct bio *bio);
+void drbd_submit_bio(struct bio *bio);
 extern int drbd_read_remote(struct drbd_device *device, struct drbd_request *req);
 extern int is_valid_ar_handle(struct drbd_request *, sector_t);
 
diff --git a/drivers/block/drbd/drbd_req.c b/drivers/block/drbd/drbd_req.c
index 13beb98a7c5a..0a2b3cb7e0bd 100644
--- a/drivers/block/drbd/drbd_req.c
+++ b/drivers/block/drbd/drbd_req.c
@@ -1597,7 +1597,7 @@ void do_submit(struct work_struct *ws)
 	}
 }
 
-blk_qc_t drbd_submit_bio(struct bio *bio)
+void drbd_submit_bio(struct bio *bio)
 {
 	struct drbd_device *device = bio->bi_bdev->bd_disk->private_data;
 
@@ -1610,7 +1610,6 @@ blk_qc_t drbd_submit_bio(struct bio *bio)
 
 	inc_ap_bio(device);
 	__drbd_make_request(device, bio);
-	return BLK_QC_T_NONE;
 }
 
 static bool net_timeout_reached(struct drbd_request *net_req,
diff --git a/drivers/block/n64cart.c b/drivers/block/n64cart.c
index 47bdf324e962..94f3c43d6da2 100644
--- a/drivers/block/n64cart.c
+++ b/drivers/block/n64cart.c
@@ -84,7 +84,7 @@ static bool n64cart_do_bvec(struct device *dev, struct bio_vec *bv, u32 pos)
 	return true;
 }
 
-static blk_qc_t n64cart_submit_bio(struct bio *bio)
+static void n64cart_submit_bio(struct bio *bio)
 {
 	struct bio_vec bvec;
 	struct bvec_iter iter;
@@ -92,16 +92,14 @@ static blk_qc_t n64cart_submit_bio(struct bio *bio)
 	u32 pos = bio->bi_iter.bi_sector << SECTOR_SHIFT;
 
 	bio_for_each_segment(bvec, bio, iter) {
-		if (!n64cart_do_bvec(dev, &bvec, pos))
-			goto io_error;
+		if (!n64cart_do_bvec(dev, &bvec, pos)) {
+			bio_io_error(bio);
+			return;
+		}
 		pos += bvec.bv_len;
 	}
 
 	bio_endio(bio);
-	return BLK_QC_T_NONE;
-io_error:
-	bio_io_error(bio);
-	return BLK_QC_T_NONE;
 }
 
 static const struct block_device_operations n64cart_fops = {
diff --git a/drivers/block/null_blk/main.c b/drivers/block/null_blk/main.c
index 5f006d9e1472..baf3ec7af3d1 100644
--- a/drivers/block/null_blk/main.c
+++ b/drivers/block/null_blk/main.c
@@ -1426,7 +1426,7 @@ static struct nullb_queue *nullb_to_queue(struct nullb *nullb)
 	return &nullb->queues[index];
 }
 
-static blk_qc_t null_submit_bio(struct bio *bio)
+static void null_submit_bio(struct bio *bio)
 {
 	sector_t sector = bio->bi_iter.bi_sector;
 	sector_t nr_sectors = bio_sectors(bio);
@@ -1438,7 +1438,6 @@ static blk_qc_t null_submit_bio(struct bio *bio)
 	cmd->bio = bio;
 
 	null_handle_cmd(cmd, sector, nr_sectors, bio_op(bio));
-	return BLK_QC_T_NONE;
 }
 
 static bool should_timeout_request(struct request *rq)
diff --git a/drivers/block/pktcdvd.c b/drivers/block/pktcdvd.c
index bd3556585122..628ed0d3f2e4 100644
--- a/drivers/block/pktcdvd.c
+++ b/drivers/block/pktcdvd.c
@@ -2402,7 +2402,7 @@ static void pkt_make_request_write(struct request_queue *q, struct bio *bio)
 	}
 }
 
-static blk_qc_t pkt_submit_bio(struct bio *bio)
+static void pkt_submit_bio(struct bio *bio)
 {
 	struct pktcdvd_device *pd;
 	char b[BDEVNAME_SIZE];
@@ -2425,7 +2425,7 @@ static blk_qc_t pkt_submit_bio(struct bio *bio)
 	 */
 	if (bio_data_dir(bio) == READ) {
 		pkt_make_request_read(pd, bio);
-		return BLK_QC_T_NONE;
+		return;
 	}
 
 	if (!test_bit(PACKET_WRITABLE, &pd->flags)) {
@@ -2457,10 +2457,9 @@ static blk_qc_t pkt_submit_bio(struct bio *bio)
 		pkt_make_request_write(bio->bi_bdev->bd_disk->queue, split);
 	} while (split != bio);
 
-	return BLK_QC_T_NONE;
+	return;
 end_io:
 	bio_io_error(bio);
-	return BLK_QC_T_NONE;
 }
 
 static void pkt_init_queue(struct pktcdvd_device *pd)
diff --git a/drivers/block/ps3vram.c b/drivers/block/ps3vram.c
index 1d738999fb69..382be2f07c49 100644
--- a/drivers/block/ps3vram.c
+++ b/drivers/block/ps3vram.c
@@ -579,7 +579,7 @@ static struct bio *ps3vram_do_bio(struct ps3_system_bus_device *dev,
 	return next;
 }
 
-static blk_qc_t ps3vram_submit_bio(struct bio *bio)
+static void ps3vram_submit_bio(struct bio *bio)
 {
 	struct ps3_system_bus_device *dev = bio->bi_bdev->bd_disk->private_data;
 	struct ps3vram_priv *priv = ps3_system_bus_get_drvdata(dev);
@@ -595,13 +595,11 @@ static blk_qc_t ps3vram_submit_bio(struct bio *bio)
 	spin_unlock_irq(&priv->lock);
 
 	if (busy)
-		return BLK_QC_T_NONE;
+		return;
 
 	do {
 		bio = ps3vram_do_bio(dev, bio);
 	} while (bio);
-
-	return BLK_QC_T_NONE;
 }
 
 static const struct block_device_operations ps3vram_fops = {
diff --git a/drivers/block/rsxx/dev.c b/drivers/block/rsxx/dev.c
index 9a28322a8cd8..a4f5a09d0937 100644
--- a/drivers/block/rsxx/dev.c
+++ b/drivers/block/rsxx/dev.c
@@ -50,7 +50,7 @@ struct rsxx_bio_meta {
 
 static struct kmem_cache *bio_meta_pool;
 
-static blk_qc_t rsxx_submit_bio(struct bio *bio);
+static void rsxx_submit_bio(struct bio *bio);
 
 /*----------------- Block Device Operations -----------------*/
 static int rsxx_blkdev_ioctl(struct block_device *bdev,
@@ -120,7 +120,7 @@ static void bio_dma_done_cb(struct rsxx_cardinfo *card,
 	}
 }
 
-static blk_qc_t rsxx_submit_bio(struct bio *bio)
+static void rsxx_submit_bio(struct bio *bio)
 {
 	struct rsxx_cardinfo *card = bio->bi_bdev->bd_disk->private_data;
 	struct rsxx_bio_meta *bio_meta;
@@ -169,7 +169,7 @@ static blk_qc_t rsxx_submit_bio(struct bio *bio)
 	if (st)
 		goto queue_err;
 
-	return BLK_QC_T_NONE;
+	return;
 
 queue_err:
 	kmem_cache_free(bio_meta_pool, bio_meta);
@@ -177,7 +177,6 @@ static blk_qc_t rsxx_submit_bio(struct bio *bio)
 	if (st)
 		bio->bi_status = st;
 	bio_endio(bio);
-	return BLK_QC_T_NONE;
 }
 
 /*----------------- Device Setup -------------------*/
diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
index cf8deecc39ef..51dab0d4bedf 100644
--- a/drivers/block/zram/zram_drv.c
+++ b/drivers/block/zram/zram_drv.c
@@ -1598,22 +1598,18 @@ static void __zram_make_request(struct zram *zram, struct bio *bio)
 /*
  * Handler function for all zram I/O requests.
  */
-static blk_qc_t zram_submit_bio(struct bio *bio)
+static void zram_submit_bio(struct bio *bio)
 {
 	struct zram *zram = bio->bi_bdev->bd_disk->private_data;
 
 	if (!valid_io_request(zram, bio->bi_iter.bi_sector,
 					bio->bi_iter.bi_size)) {
 		atomic64_inc(&zram->stats.invalid_io);
-		goto error;
+		bio_io_error(bio);
+		return;
 	}
 
 	__zram_make_request(zram, bio);
-	return BLK_QC_T_NONE;
-
-error:
-	bio_io_error(bio);
-	return BLK_QC_T_NONE;
 }
 
 static void zram_slot_free_notify(struct block_device *bdev,
diff --git a/drivers/lightnvm/pblk-init.c b/drivers/lightnvm/pblk-init.c
index 5924f09c217b..6716003d4cb6 100644
--- a/drivers/lightnvm/pblk-init.c
+++ b/drivers/lightnvm/pblk-init.c
@@ -47,7 +47,7 @@ static struct pblk_global_caches pblk_caches = {
 
 struct bio_set pblk_bio_set;
 
-static blk_qc_t pblk_submit_bio(struct bio *bio)
+static void pblk_submit_bio(struct bio *bio)
 {
 	struct pblk *pblk = bio->bi_bdev->bd_disk->queue->queuedata;
 
@@ -55,7 +55,7 @@ static blk_qc_t pblk_submit_bio(struct bio *bio)
 		pblk_discard(pblk, bio);
 		if (!(bio->bi_opf & REQ_PREFLUSH)) {
 			bio_endio(bio);
-			return BLK_QC_T_NONE;
+			return;
 		}
 	}
 
@@ -75,8 +75,6 @@ static blk_qc_t pblk_submit_bio(struct bio *bio)
 
 		pblk_write_to_cache(pblk, bio, PBLK_IOTYPE_USER);
 	}
-
-	return BLK_QC_T_NONE;
 }
 
 static const struct block_device_operations pblk_bops = {
diff --git a/drivers/md/bcache/request.c b/drivers/md/bcache/request.c
index 29c231758293..b549147a567f 100644
--- a/drivers/md/bcache/request.c
+++ b/drivers/md/bcache/request.c
@@ -1169,7 +1169,7 @@ static void quit_max_writeback_rate(struct cache_set *c,
 
 /* Cached devices - read & write stuff */
 
-blk_qc_t cached_dev_submit_bio(struct bio *bio)
+void cached_dev_submit_bio(struct bio *bio)
 {
 	struct search *s;
 	struct block_device *orig_bdev = bio->bi_bdev;
@@ -1182,7 +1182,7 @@ blk_qc_t cached_dev_submit_bio(struct bio *bio)
 		     dc->io_disable)) {
 		bio->bi_status = BLK_STS_IOERR;
 		bio_endio(bio);
-		return BLK_QC_T_NONE;
+		return;
 	}
 
 	if (likely(d->c)) {
@@ -1228,8 +1228,6 @@ blk_qc_t cached_dev_submit_bio(struct bio *bio)
 	} else
 		/* I/O request sent to backing device */
 		detached_dev_do_request(d, bio, orig_bdev, start_time);
-
-	return BLK_QC_T_NONE;
 }
 
 static int cached_dev_ioctl(struct bcache_device *d, fmode_t mode,
@@ -1279,7 +1277,7 @@ static void flash_dev_nodata(struct closure *cl)
 	continue_at(cl, search_free, NULL);
 }
 
-blk_qc_t flash_dev_submit_bio(struct bio *bio)
+void flash_dev_submit_bio(struct bio *bio)
 {
 	struct search *s;
 	struct closure *cl;
@@ -1288,7 +1286,7 @@ blk_qc_t flash_dev_submit_bio(struct bio *bio)
 	if (unlikely(d->c && test_bit(CACHE_SET_IO_DISABLE, &d->c->flags))) {
 		bio->bi_status = BLK_STS_IOERR;
 		bio_endio(bio);
-		return BLK_QC_T_NONE;
+		return;
 	}
 
 	s = search_alloc(bio, d, bio->bi_bdev, bio_start_io_acct(bio));
@@ -1304,7 +1302,7 @@ blk_qc_t flash_dev_submit_bio(struct bio *bio)
 		continue_at_nobarrier(&s->cl,
 				      flash_dev_nodata,
 				      bcache_wq);
-		return BLK_QC_T_NONE;
+		return;
 	} else if (bio_data_dir(bio)) {
 		bch_keybuf_check_overlapping(&s->iop.c->moving_gc_keys,
 					&KEY(d->id, bio->bi_iter.bi_sector, 0),
@@ -1320,7 +1318,6 @@ blk_qc_t flash_dev_submit_bio(struct bio *bio)
 	}
 
 	continue_at(cl, search_free, NULL);
-	return BLK_QC_T_NONE;
 }
 
 static int flash_dev_ioctl(struct bcache_device *d, fmode_t mode,
diff --git a/drivers/md/bcache/request.h b/drivers/md/bcache/request.h
index 82b38366a95d..38ab4856eaab 100644
--- a/drivers/md/bcache/request.h
+++ b/drivers/md/bcache/request.h
@@ -37,10 +37,10 @@ unsigned int bch_get_congested(const struct cache_set *c);
 void bch_data_insert(struct closure *cl);
 
 void bch_cached_dev_request_init(struct cached_dev *dc);
-blk_qc_t cached_dev_submit_bio(struct bio *bio);
+void cached_dev_submit_bio(struct bio *bio);
 
 void bch_flash_dev_request_init(struct bcache_device *d);
-blk_qc_t flash_dev_submit_bio(struct bio *bio);
+void flash_dev_submit_bio(struct bio *bio);
 
 extern struct kmem_cache *bch_search_cache;
 
diff --git a/drivers/md/dm.c b/drivers/md/dm.c
index ca2aedd8ee7d..fe2b5e60f981 100644
--- a/drivers/md/dm.c
+++ b/drivers/md/dm.c
@@ -1292,14 +1292,13 @@ static noinline void __set_swap_bios_limit(struct mapped_device *md, int latch)
 	mutex_unlock(&md->swap_bios_lock);
 }
 
-static blk_qc_t __map_bio(struct dm_target_io *tio)
+static void __map_bio(struct dm_target_io *tio)
 {
 	int r;
 	sector_t sector;
 	struct bio *clone = &tio->clone;
 	struct dm_io *io = tio->io;
 	struct dm_target *ti = tio->ti;
-	blk_qc_t ret = BLK_QC_T_NONE;
 
 	clone->bi_end_io = clone_endio;
 
@@ -1326,7 +1325,7 @@ static blk_qc_t __map_bio(struct dm_target_io *tio)
 	case DM_MAPIO_REMAPPED:
 		/* the bio has been remapped so dispatch it */
 		trace_block_bio_remap(clone, bio_dev(io->orig_bio), sector);
-		ret = submit_bio_noacct(clone);
+		submit_bio_noacct(clone);
 		break;
 	case DM_MAPIO_KILL:
 		if (unlikely(swap_bios_limit(ti, clone))) {
@@ -1348,8 +1347,6 @@ static blk_qc_t __map_bio(struct dm_target_io *tio)
 		DMWARN("unimplemented target map return value: %d", r);
 		BUG();
 	}
-
-	return ret;
 }
 
 static void bio_setup_sector(struct bio *bio, sector_t sector, unsigned len)
@@ -1436,7 +1433,7 @@ static void alloc_multiple_bios(struct bio_list *blist, struct clone_info *ci,
 	}
 }
 
-static blk_qc_t __clone_and_map_simple_bio(struct clone_info *ci,
+static void __clone_and_map_simple_bio(struct clone_info *ci,
 					   struct dm_target_io *tio, unsigned *len)
 {
 	struct bio *clone = &tio->clone;
@@ -1446,8 +1443,7 @@ static blk_qc_t __clone_and_map_simple_bio(struct clone_info *ci,
 	__bio_clone_fast(clone, ci->bio);
 	if (len)
 		bio_setup_sector(clone, ci->sector, *len);
-
-	return __map_bio(tio);
+	__map_bio(tio);
 }
 
 static void __send_duplicate_bios(struct clone_info *ci, struct dm_target *ti,
@@ -1461,7 +1457,7 @@ static void __send_duplicate_bios(struct clone_info *ci, struct dm_target *ti,
 
 	while ((bio = bio_list_pop(&blist))) {
 		tio = container_of(bio, struct dm_target_io, clone);
-		(void) __clone_and_map_simple_bio(ci, tio, len);
+		__clone_and_map_simple_bio(ci, tio, len);
 	}
 }
 
@@ -1505,7 +1501,7 @@ static int __clone_and_map_data_bio(struct clone_info *ci, struct dm_target *ti,
 		free_tio(tio);
 		return r;
 	}
-	(void) __map_bio(tio);
+	__map_bio(tio);
 
 	return 0;
 }
@@ -1620,11 +1616,10 @@ static void init_clone_info(struct clone_info *ci, struct mapped_device *md,
 /*
  * Entry point to split a bio into clones and submit them to the targets.
  */
-static blk_qc_t __split_and_process_bio(struct mapped_device *md,
+static void __split_and_process_bio(struct mapped_device *md,
 					struct dm_table *map, struct bio *bio)
 {
 	struct clone_info ci;
-	blk_qc_t ret = BLK_QC_T_NONE;
 	int error = 0;
 
 	init_clone_info(&ci, md, map, bio);
@@ -1667,19 +1662,17 @@ static blk_qc_t __split_and_process_bio(struct mapped_device *md,
 
 			bio_chain(b, bio);
 			trace_block_split(b, bio->bi_iter.bi_sector);
-			ret = submit_bio_noacct(bio);
+			submit_bio_noacct(bio);
 		}
 	}
 
 	/* drop the extra reference count */
 	dec_pending(ci.io, errno_to_blk_status(error));
-	return ret;
 }
 
-static blk_qc_t dm_submit_bio(struct bio *bio)
+static void dm_submit_bio(struct bio *bio)
 {
 	struct mapped_device *md = bio->bi_bdev->bd_disk->private_data;
-	blk_qc_t ret = BLK_QC_T_NONE;
 	int srcu_idx;
 	struct dm_table *map;
 
@@ -1709,10 +1702,9 @@ static blk_qc_t dm_submit_bio(struct bio *bio)
 	if (is_abnormal_io(bio))
 		blk_queue_split(&bio);
 
-	ret = __split_and_process_bio(md, map, bio);
+	__split_and_process_bio(md, map, bio);
 out:
 	dm_put_live_table(md, srcu_idx);
-	return ret;
 }
 
 /*-----------------------------------------------------------------
diff --git a/drivers/md/md.c b/drivers/md/md.c
index 49f897fbb89b..c9227a73ae86 100644
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -465,19 +465,19 @@ static void md_end_io(struct bio *bio)
 		bio->bi_end_io(bio);
 }
 
-static blk_qc_t md_submit_bio(struct bio *bio)
+static void md_submit_bio(struct bio *bio)
 {
 	const int rw = bio_data_dir(bio);
 	struct mddev *mddev = bio->bi_bdev->bd_disk->private_data;
 
 	if (mddev == NULL || mddev->pers == NULL) {
 		bio_io_error(bio);
-		return BLK_QC_T_NONE;
+		return;
 	}
 
 	if (unlikely(test_bit(MD_BROKEN, &mddev->flags)) && (rw == WRITE)) {
 		bio_io_error(bio);
-		return BLK_QC_T_NONE;
+		return;
 	}
 
 	blk_queue_split(&bio);
@@ -486,7 +486,7 @@ static blk_qc_t md_submit_bio(struct bio *bio)
 		if (bio_sectors(bio) != 0)
 			bio->bi_status = BLK_STS_IOERR;
 		bio_endio(bio);
-		return BLK_QC_T_NONE;
+		return;
 	}
 
 	if (bio->bi_end_io != md_end_io) {
@@ -508,8 +508,6 @@ static blk_qc_t md_submit_bio(struct bio *bio)
 	bio->bi_opf &= ~REQ_NOMERGE;
 
 	md_handle_request(mddev, bio);
-
-	return BLK_QC_T_NONE;
 }
 
 /* mddev_suspend makes sure no new requests are submitted
diff --git a/drivers/nvdimm/blk.c b/drivers/nvdimm/blk.c
index 7b9556291eb1..90c202cd39dd 100644
--- a/drivers/nvdimm/blk.c
+++ b/drivers/nvdimm/blk.c
@@ -162,7 +162,7 @@ static int nsblk_do_bvec(struct nd_namespace_blk *nsblk,
 	return err;
 }
 
-static blk_qc_t nd_blk_submit_bio(struct bio *bio)
+static void nd_blk_submit_bio(struct bio *bio)
 {
 	struct bio_integrity_payload *bip;
 	struct nd_namespace_blk *nsblk = bio->bi_bdev->bd_disk->private_data;
@@ -173,7 +173,7 @@ static blk_qc_t nd_blk_submit_bio(struct bio *bio)
 	bool do_acct;
 
 	if (!bio_integrity_prep(bio))
-		return BLK_QC_T_NONE;
+		return;
 
 	bip = bio_integrity(bio);
 	rw = bio_data_dir(bio);
@@ -199,7 +199,6 @@ static blk_qc_t nd_blk_submit_bio(struct bio *bio)
 		bio_end_io_acct(bio, start);
 
 	bio_endio(bio);
-	return BLK_QC_T_NONE;
 }
 
 static int nsblk_rw_bytes(struct nd_namespace_common *ndns,
diff --git a/drivers/nvdimm/btt.c b/drivers/nvdimm/btt.c
index 18a267d5073f..be739e701f79 100644
--- a/drivers/nvdimm/btt.c
+++ b/drivers/nvdimm/btt.c
@@ -1440,7 +1440,7 @@ static int btt_do_bvec(struct btt *btt, struct bio_integrity_payload *bip,
 	return ret;
 }
 
-static blk_qc_t btt_submit_bio(struct bio *bio)
+static void btt_submit_bio(struct bio *bio)
 {
 	struct bio_integrity_payload *bip = bio_integrity(bio);
 	struct btt *btt = bio->bi_bdev->bd_disk->private_data;
@@ -1451,7 +1451,7 @@ static blk_qc_t btt_submit_bio(struct bio *bio)
 	bool do_acct;
 
 	if (!bio_integrity_prep(bio))
-		return BLK_QC_T_NONE;
+		return;
 
 	do_acct = blk_queue_io_stat(bio->bi_bdev->bd_disk->queue);
 	if (do_acct)
@@ -1483,7 +1483,6 @@ static blk_qc_t btt_submit_bio(struct bio *bio)
 		bio_end_io_acct(bio, start);
 
 	bio_endio(bio);
-	return BLK_QC_T_NONE;
 }
 
 static int btt_rw_page(struct block_device *bdev, sector_t sector,
diff --git a/drivers/nvdimm/pmem.c b/drivers/nvdimm/pmem.c
index ed10a8b66068..488312effaa8 100644
--- a/drivers/nvdimm/pmem.c
+++ b/drivers/nvdimm/pmem.c
@@ -190,7 +190,7 @@ static blk_status_t pmem_do_write(struct pmem_device *pmem,
 	return rc;
 }
 
-static blk_qc_t pmem_submit_bio(struct bio *bio)
+static void pmem_submit_bio(struct bio *bio)
 {
 	int ret = 0;
 	blk_status_t rc = 0;
@@ -229,7 +229,6 @@ static blk_qc_t pmem_submit_bio(struct bio *bio)
 		bio->bi_status = errno_to_blk_status(ret);
 
 	bio_endio(bio);
-	return BLK_QC_T_NONE;
 }
 
 static int pmem_rw_page(struct block_device *bdev, sector_t sector,
diff --git a/drivers/nvme/host/core.c b/drivers/nvme/host/core.c
index c58dde3460e9..a47e705dafa9 100644
--- a/drivers/nvme/host/core.c
+++ b/drivers/nvme/host/core.c
@@ -1032,7 +1032,7 @@ static void nvme_execute_rq_polled(struct request_queue *q,
 	blk_execute_rq_nowait(bd_disk, rq, at_head, nvme_end_sync_rq);
 
 	while (!completion_done(&wait)) {
-		blk_poll(q, request_to_qc_t(rq->mq_hctx, rq), 0);
+		bio_poll(rq->bio, 0);
 		cond_resched();
 	}
 }
diff --git a/drivers/nvme/host/multipath.c b/drivers/nvme/host/multipath.c
index 0551796517e6..74455960337b 100644
--- a/drivers/nvme/host/multipath.c
+++ b/drivers/nvme/host/multipath.c
@@ -297,12 +297,11 @@ static bool nvme_available_path(struct nvme_ns_head *head)
 	return false;
 }
 
-static blk_qc_t nvme_ns_head_submit_bio(struct bio *bio)
+static void nvme_ns_head_submit_bio(struct bio *bio)
 {
 	struct nvme_ns_head *head = bio->bi_bdev->bd_disk->private_data;
 	struct device *dev = disk_to_dev(head->disk);
 	struct nvme_ns *ns;
-	blk_qc_t ret = BLK_QC_T_NONE;
 	int srcu_idx;
 
 	/*
@@ -319,7 +318,7 @@ static blk_qc_t nvme_ns_head_submit_bio(struct bio *bio)
 		bio->bi_opf |= REQ_NVME_MPATH;
 		trace_block_bio_remap(bio, disk_devt(ns->head->disk),
 				      bio->bi_iter.bi_sector);
-		ret = submit_bio_noacct(bio);
+		submit_bio_noacct(bio);
 	} else if (nvme_available_path(head)) {
 		dev_warn_ratelimited(dev, "no usable path - requeuing I/O\n");
 
@@ -334,7 +333,6 @@ static blk_qc_t nvme_ns_head_submit_bio(struct bio *bio)
 	}
 
 	srcu_read_unlock(&head->srcu, srcu_idx);
-	return ret;
 }
 
 static int nvme_ns_head_open(struct block_device *bdev, fmode_t mode)
diff --git a/drivers/s390/block/dcssblk.c b/drivers/s390/block/dcssblk.c
index da33cb4cba28..f17582ade60b 100644
--- a/drivers/s390/block/dcssblk.c
+++ b/drivers/s390/block/dcssblk.c
@@ -31,7 +31,7 @@
 
 static int dcssblk_open(struct block_device *bdev, fmode_t mode);
 static void dcssblk_release(struct gendisk *disk, fmode_t mode);
-static blk_qc_t dcssblk_submit_bio(struct bio *bio);
+static void dcssblk_submit_bio(struct bio *bio);
 static long dcssblk_dax_direct_access(struct dax_device *dax_dev, pgoff_t pgoff,
 		long nr_pages, void **kaddr, pfn_t *pfn);
 
@@ -865,7 +865,7 @@ dcssblk_release(struct gendisk *disk, fmode_t mode)
 	up_write(&dcssblk_devices_sem);
 }
 
-static blk_qc_t
+static void
 dcssblk_submit_bio(struct bio *bio)
 {
 	struct dcssblk_dev_info *dev_info;
@@ -919,10 +919,9 @@ dcssblk_submit_bio(struct bio *bio)
 		bytes_done += bvec.bv_len;
 	}
 	bio_endio(bio);
-	return BLK_QC_T_NONE;
+	return;
 fail:
 	bio_io_error(bio);
-	return BLK_QC_T_NONE;
 }
 
 static long
diff --git a/drivers/s390/block/xpram.c b/drivers/s390/block/xpram.c
index d1ed39162943..bb129e31df77 100644
--- a/drivers/s390/block/xpram.c
+++ b/drivers/s390/block/xpram.c
@@ -182,7 +182,7 @@ static unsigned long xpram_highest_page_index(void)
 /*
  * Block device make request function.
  */
-static blk_qc_t xpram_submit_bio(struct bio *bio)
+static void xpram_submit_bio(struct bio *bio)
 {
 	xpram_device_t *xdev = bio->bi_bdev->bd_disk->private_data;
 	struct bio_vec bvec;
@@ -224,10 +224,9 @@ static blk_qc_t xpram_submit_bio(struct bio *bio)
 		}
 	}
 	bio_endio(bio);
-	return BLK_QC_T_NONE;
+	return;
 fail:
 	bio_io_error(bio);
-	return BLK_QC_T_NONE;
 }
 
 static int xpram_getgeo(struct block_device *bdev, struct hd_geometry *geo)
diff --git a/fs/block_dev.c b/fs/block_dev.c
index fd12a05cb3a9..e722a4e86e35 100644
--- a/fs/block_dev.c
+++ b/fs/block_dev.c
@@ -239,7 +239,6 @@ __blkdev_direct_IO_simple(struct kiocb *iocb, struct iov_iter *iter,
 	bool should_dirty = false;
 	struct bio bio;
 	ssize_t ret;
-	blk_qc_t qc;
 
 	if ((pos | iov_iter_alignment(iter)) &
 	    (bdev_logical_block_size(bdev) - 1))
@@ -280,13 +279,12 @@ __blkdev_direct_IO_simple(struct kiocb *iocb, struct iov_iter *iter,
 	if (iocb->ki_flags & IOCB_HIPRI)
 		bio_set_polled(&bio, iocb);
 
-	qc = submit_bio(&bio);
+	submit_bio(&bio);
 	for (;;) {
 		set_current_state(TASK_UNINTERRUPTIBLE);
 		if (!READ_ONCE(bio.bi_private))
 			break;
-		if (!(iocb->ki_flags & IOCB_HIPRI) ||
-		    !blk_poll(bdev_get_queue(bdev), qc, 0))
+		if (!(iocb->ki_flags & IOCB_HIPRI) || !bio_poll(&bio, 0))
 			blk_io_schedule();
 	}
 	__set_current_state(TASK_RUNNING);
@@ -319,14 +317,6 @@ struct blkdev_dio {
 
 static struct bio_set blkdev_dio_pool;
 
-static int blkdev_iopoll(struct kiocb *kiocb, unsigned int flags)
-{
-	struct block_device *bdev = I_BDEV(kiocb->ki_filp->f_mapping->host);
-	struct request_queue *q = bdev_get_queue(bdev);
-
-	return blk_poll(q, READ_ONCE(kiocb->ki_cookie), flags);
-}
-
 static void blkdev_bio_end_io(struct bio *bio)
 {
 	struct blkdev_dio *dio = bio->bi_private;
@@ -340,6 +330,8 @@ static void blkdev_bio_end_io(struct bio *bio)
 			struct kiocb *iocb = dio->iocb;
 			ssize_t ret;
 
+			WRITE_ONCE(iocb->private, NULL);
+
 			if (likely(!dio->bio.bi_status)) {
 				ret = dio->size;
 				iocb->ki_pos += ret;
@@ -378,7 +370,6 @@ static ssize_t __blkdev_direct_IO(struct kiocb *iocb, struct iov_iter *iter,
 	bool is_poll = (iocb->ki_flags & IOCB_HIPRI), do_poll = false;
 	bool is_read = (iov_iter_rw(iter) == READ), is_sync;
 	loff_t pos = iocb->ki_pos;
-	blk_qc_t qc = BLK_QC_T_NONE;
 	int ret = 0;
 
 	if ((pos | iov_iter_alignment(iter)) &
@@ -453,10 +444,10 @@ static ssize_t __blkdev_direct_IO(struct kiocb *iocb, struct iov_iter *iter,
 			bio_set_polled(bio, iocb);
 			do_poll = true;
 		}
-		qc = submit_bio(bio);
+		submit_bio(bio);
 		if (!nr_pages) {
 			if (do_poll)
-				WRITE_ONCE(iocb->ki_cookie, qc);
+				WRITE_ONCE(iocb->private, bio);
 			break;
 		}
 		bio = bio_alloc(GFP_KERNEL, nr_pages);
@@ -473,7 +464,7 @@ static ssize_t __blkdev_direct_IO(struct kiocb *iocb, struct iov_iter *iter,
 		if (!READ_ONCE(dio->waiter))
 			break;
 
-		if (!do_poll || !blk_poll(bdev_get_queue(bdev), qc, 0))
+		if (!do_poll || !bio_poll(bio, 0))
 			blk_io_schedule();
 	}
 	__set_current_state(TASK_RUNNING);
@@ -1832,7 +1823,7 @@ const struct file_operations def_blk_fops = {
 	.llseek		= block_llseek,
 	.read_iter	= blkdev_read_iter,
 	.write_iter	= blkdev_write_iter,
-	.iopoll		= blkdev_iopoll,
+	.iopoll		= iocb_bio_iopoll,
 	.mmap		= generic_file_mmap,
 	.fsync		= blkdev_fsync,
 	.unlocked_ioctl	= block_ioctl,
diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index 4af336008b12..60ef00dfec8b 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -8103,7 +8103,7 @@ static struct btrfs_dio_private *btrfs_create_dio_private(struct bio *dio_bio,
 	return dip;
 }
 
-static blk_qc_t btrfs_submit_direct(struct inode *inode, struct iomap *iomap,
+static void btrfs_submit_direct(struct inode *inode, struct iomap *iomap,
 		struct bio *dio_bio, loff_t file_offset)
 {
 	const bool write = (btrfs_op(dio_bio) == BTRFS_MAP_WRITE);
@@ -8132,7 +8132,7 @@ static blk_qc_t btrfs_submit_direct(struct inode *inode, struct iomap *iomap,
 		}
 		dio_bio->bi_status = BLK_STS_RESOURCE;
 		bio_endio(dio_bio);
-		return BLK_QC_T_NONE;
+		return;
 	}
 
 	if (!write) {
@@ -8226,15 +8226,13 @@ static blk_qc_t btrfs_submit_direct(struct inode *inode, struct iomap *iomap,
 
 		free_extent_map(em);
 	} while (submit_len > 0);
-	return BLK_QC_T_NONE;
+	return;
 
 out_err_em:
 	free_extent_map(em);
 out_err:
 	dip->dio_bio->bi_status = status;
 	btrfs_dio_private_put(dip);
-
-	return BLK_QC_T_NONE;
 }
 
 const struct iomap_ops btrfs_dio_iomap_ops = {
diff --git a/fs/ext4/file.c b/fs/ext4/file.c
index 816dedcbd541..6146c4203fda 100644
--- a/fs/ext4/file.c
+++ b/fs/ext4/file.c
@@ -913,7 +913,7 @@ const struct file_operations ext4_file_operations = {
 	.llseek		= ext4_llseek,
 	.read_iter	= ext4_file_read_iter,
 	.write_iter	= ext4_file_write_iter,
-	.iopoll		= iomap_dio_iopoll,
+	.iopoll		= iocb_bio_iopoll,
 	.unlocked_ioctl = ext4_ioctl,
 #ifdef CONFIG_COMPAT
 	.compat_ioctl	= ext4_compat_ioctl,
diff --git a/fs/gfs2/file.c b/fs/gfs2/file.c
index a0b542d84cd9..d51d0c663bde 100644
--- a/fs/gfs2/file.c
+++ b/fs/gfs2/file.c
@@ -1334,7 +1334,7 @@ const struct file_operations gfs2_file_fops = {
 	.llseek		= gfs2_llseek,
 	.read_iter	= gfs2_file_read_iter,
 	.write_iter	= gfs2_file_write_iter,
-	.iopoll		= iomap_dio_iopoll,
+	.iopoll		= iocb_bio_iopoll,
 	.unlocked_ioctl	= gfs2_ioctl,
 	.compat_ioctl	= gfs2_compat_ioctl,
 	.mmap		= gfs2_mmap,
@@ -1367,7 +1367,7 @@ const struct file_operations gfs2_file_fops_nolock = {
 	.llseek		= gfs2_llseek,
 	.read_iter	= gfs2_file_read_iter,
 	.write_iter	= gfs2_file_write_iter,
-	.iopoll		= iomap_dio_iopoll,
+	.iopoll		= iocb_bio_iopoll,
 	.unlocked_ioctl	= gfs2_ioctl,
 	.compat_ioctl	= gfs2_compat_ioctl,
 	.mmap		= gfs2_mmap,
diff --git a/fs/iomap/direct-io.c b/fs/iomap/direct-io.c
index 9b6c26da3a2d..76bc7c4b0deb 100644
--- a/fs/iomap/direct-io.c
+++ b/fs/iomap/direct-io.c
@@ -38,8 +38,7 @@ struct iomap_dio {
 		struct {
 			struct iov_iter		*iter;
 			struct task_struct	*waiter;
-			struct request_queue	*last_queue;
-			blk_qc_t		cookie;
+			struct bio		*poll_bio;
 		} submit;
 
 		/* used for aio completion: */
@@ -49,31 +48,21 @@ struct iomap_dio {
 	};
 };
 
-int iomap_dio_iopoll(struct kiocb *kiocb, unsigned int flags)
-{
-	struct request_queue *q = READ_ONCE(kiocb->private);
-
-	if (!q)
-		return 0;
-	return blk_poll(q, READ_ONCE(kiocb->ki_cookie), flags);
-}
-EXPORT_SYMBOL_GPL(iomap_dio_iopoll);
-
 static void iomap_dio_submit_bio(struct iomap_dio *dio, struct iomap *iomap,
 		struct bio *bio, loff_t pos)
 {
 	atomic_inc(&dio->ref);
 
-	if (dio->iocb->ki_flags & IOCB_HIPRI)
+	if (dio->iocb->ki_flags & IOCB_HIPRI) {
 		bio_set_polled(bio, dio->iocb);
+		dio->submit.poll_bio = bio;
+	}
 
-	dio->submit.last_queue = bdev_get_queue(iomap->bdev);
 	if (dio->dops && dio->dops->submit_io)
-		dio->submit.cookie = dio->dops->submit_io(
-				file_inode(dio->iocb->ki_filp),
-				iomap, bio, pos);
+		dio->dops->submit_io(file_inode(dio->iocb->ki_filp), iomap, bio,
+				     pos);
 	else
-		dio->submit.cookie = submit_bio(bio);
+		submit_bio(bio);
 }
 
 ssize_t iomap_dio_complete(struct iomap_dio *dio)
@@ -166,9 +155,11 @@ static void iomap_dio_bio_end_io(struct bio *bio)
 		} else if (dio->flags & IOMAP_DIO_WRITE) {
 			struct inode *inode = file_inode(dio->iocb->ki_filp);
 
+			WRITE_ONCE(dio->iocb->private, NULL);
 			INIT_WORK(&dio->aio.work, iomap_dio_complete_work);
 			queue_work(inode->i_sb->s_dio_done_wq, &dio->aio.work);
 		} else {
+			WRITE_ONCE(dio->iocb->private, NULL);
 			iomap_dio_complete_work(&dio->aio.work);
 		}
 	}
@@ -492,8 +483,7 @@ __iomap_dio_rw(struct kiocb *iocb, struct iov_iter *iter,
 
 	dio->submit.iter = iter;
 	dio->submit.waiter = current;
-	dio->submit.cookie = BLK_QC_T_NONE;
-	dio->submit.last_queue = NULL;
+	dio->submit.poll_bio = NULL;
 
 	if (iov_iter_rw(iter) == READ) {
 		if (pos >= dio->i_size)
@@ -609,8 +599,7 @@ __iomap_dio_rw(struct kiocb *iocb, struct iov_iter *iter,
 	if (dio->flags & IOMAP_DIO_WRITE_FUA)
 		dio->flags &= ~IOMAP_DIO_NEED_SYNC;
 
-	WRITE_ONCE(iocb->ki_cookie, dio->submit.cookie);
-	WRITE_ONCE(iocb->private, dio->submit.last_queue);
+	WRITE_ONCE(iocb->private, dio->submit.poll_bio);
 
 	/*
 	 * We are about to drop our additional submission reference, which
@@ -637,10 +626,8 @@ __iomap_dio_rw(struct kiocb *iocb, struct iov_iter *iter,
 			if (!READ_ONCE(dio->submit.waiter))
 				break;
 
-			if (!(iocb->ki_flags & IOCB_HIPRI) ||
-			    !dio->submit.last_queue ||
-			    !blk_poll(dio->submit.last_queue,
-					 dio->submit.cookie, 0))
+			if (!dio->submit.poll_bio ||
+			    !bio_poll(dio->submit.poll_bio, 0))
 				blk_io_schedule();
 		}
 		__set_current_state(TASK_RUNNING);
diff --git a/fs/xfs/xfs_file.c b/fs/xfs/xfs_file.c
index 396ef36dcd0a..d33f6e8bd313 100644
--- a/fs/xfs/xfs_file.c
+++ b/fs/xfs/xfs_file.c
@@ -1429,7 +1429,7 @@ const struct file_operations xfs_file_operations = {
 	.write_iter	= xfs_file_write_iter,
 	.splice_read	= generic_file_splice_read,
 	.splice_write	= iter_file_splice_write,
-	.iopoll		= iomap_dio_iopoll,
+	.iopoll		= iocb_bio_iopoll,
 	.unlocked_ioctl	= xfs_file_ioctl,
 #ifdef CONFIG_COMPAT
 	.compat_ioctl	= xfs_file_compat_ioctl,
diff --git a/fs/zonefs/super.c b/fs/zonefs/super.c
index cd145d318b17..2db3ba568bcf 100644
--- a/fs/zonefs/super.c
+++ b/fs/zonefs/super.c
@@ -1143,7 +1143,7 @@ static const struct file_operations zonefs_file_operations = {
 	.write_iter	= zonefs_file_write_iter,
 	.splice_read	= generic_file_splice_read,
 	.splice_write	= iter_file_splice_write,
-	.iopoll		= iomap_dio_iopoll,
+	.iopoll		= iocb_bio_iopoll,
 };
 
 static struct kmem_cache *zonefs_inode_cachep;
diff --git a/include/linux/bio.h b/include/linux/bio.h
index 439a70bc42e2..37a63c0b5c39 100644
--- a/include/linux/bio.h
+++ b/include/linux/bio.h
@@ -426,7 +426,7 @@ static inline struct bio *bio_alloc(gfp_t gfp_mask, unsigned short nr_iovecs)
 	return bio_alloc_bioset(gfp_mask, nr_iovecs, &fs_bio_set);
 }
 
-extern blk_qc_t submit_bio(struct bio *);
+void submit_bio(struct bio *bio);
 
 extern void bio_endio(struct bio *);
 
diff --git a/include/linux/blk-mq.h b/include/linux/blk-mq.h
index 359486940fa0..8a3be0c65d8e 100644
--- a/include/linux/blk-mq.h
+++ b/include/linux/blk-mq.h
@@ -148,9 +148,9 @@ struct blk_mq_hw_ctx {
 	/** @kobj: Kernel object for sysfs. */
 	struct kobject		kobj;
 
-	/** @poll_considered: Count times blk_poll() was called. */
+	/** @poll_considered: Count times blk_mq_poll() was called. */
 	unsigned long		poll_considered;
-	/** @poll_invoked: Count how many requests blk_poll() polled. */
+	/** @poll_invoked: Count how many requests blk_mq_poll() polled. */
 	unsigned long		poll_invoked;
 	/** @poll_success: Count how many polled requests were completed. */
 	unsigned long		poll_success;
@@ -595,16 +595,6 @@ static inline void *blk_mq_rq_to_pdu(struct request *rq)
 	for ((i) = 0; (i) < (hctx)->nr_ctx &&				\
 	     ({ ctx = (hctx)->ctxs[(i)]; 1; }); (i)++)
 
-static inline blk_qc_t request_to_qc_t(struct blk_mq_hw_ctx *hctx,
-		struct request *rq)
-{
-	if (rq->tag != -1)
-		return rq->tag | (hctx->queue_num << BLK_QC_T_SHIFT);
-
-	return rq->internal_tag | (hctx->queue_num << BLK_QC_T_SHIFT) |
-			BLK_QC_T_INTERNAL;
-}
-
 static inline void blk_mq_cleanup_rq(struct request *rq)
 {
 	if (rq->q->mq_ops->cleanup_rq)
@@ -623,7 +613,6 @@ static inline void blk_rq_bio_prep(struct request *rq, struct bio *bio,
 		rq->rq_disk = bio->bi_bdev->bd_disk;
 }
 
-blk_qc_t blk_mq_submit_bio(struct bio *bio);
 void blk_mq_hctx_set_fq_lock_class(struct blk_mq_hw_ctx *hctx,
 		struct lock_class_key *key);
 
diff --git a/include/linux/blk_types.h b/include/linux/blk_types.h
index ac60432752e3..8a232ea17820 100644
--- a/include/linux/blk_types.h
+++ b/include/linux/blk_types.h
@@ -216,6 +216,9 @@ static inline void bio_issue_init(struct bio_issue *issue,
 			((u64)size << BIO_ISSUE_SIZE_SHIFT));
 }
 
+typedef unsigned int blk_qc_t;
+#define BLK_QC_T_NONE		-1U
+
 /*
  * main unit of I/O for the block layer and lower layers (ie drivers and
  * stacking drivers)
@@ -235,8 +238,8 @@ struct bio {
 
 	struct bvec_iter	bi_iter;
 
+	blk_qc_t		bi_cookie;
 	bio_end_io_t		*bi_end_io;
-
 	void			*bi_private;
 #ifdef CONFIG_BLK_CGROUP
 	/*
@@ -392,7 +395,7 @@ enum req_flag_bits {
 	/* command specific flags for REQ_OP_WRITE_ZEROES: */
 	__REQ_NOUNMAP,		/* do not free blocks when zeroing */
 
-	__REQ_POLLED,		/* caller polls for completion using blk_poll */
+	__REQ_POLLED,		/* caller polls for completion using bio_poll */
 
 	/* for driver use */
 	__REQ_DRV,
@@ -505,11 +508,6 @@ static inline int op_stat_group(unsigned int op)
 	return op_is_write(op);
 }
 
-typedef unsigned int blk_qc_t;
-#define BLK_QC_T_NONE		-1U
-#define BLK_QC_T_SHIFT		16
-#define BLK_QC_T_INTERNAL	(1U << 31)
-
 struct blk_rq_stat {
 	u64 mean;
 	u64 min;
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index 273b86714c7e..b5a5d747614b 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -37,6 +37,7 @@ struct sg_io_hdr;
 struct bsg_job;
 struct blkcg_gq;
 struct blk_flush_queue;
+struct kiocb;
 struct pr_ops;
 struct rq_qos;
 struct blk_queue_stats;
@@ -901,7 +902,7 @@ static inline void rq_flush_dcache_pages(struct request *rq)
 
 extern int blk_register_queue(struct gendisk *disk);
 extern void blk_unregister_queue(struct gendisk *disk);
-blk_qc_t submit_bio_noacct(struct bio *bio);
+void submit_bio_noacct(struct bio *bio);
 extern void blk_rq_init(struct request_queue *q, struct request *rq);
 extern void blk_put_request(struct request *);
 extern struct request *blk_get_request(struct request_queue *, unsigned int op,
@@ -951,7 +952,8 @@ blk_status_t errno_to_blk_status(int errno);
 #define BLK_POLL_ONESHOT		(1 << 0)
 /* do not sleep to wait for the expected completion time */
 #define BLK_POLL_NOSLEEP		(1 << 1)
-int blk_poll(struct request_queue *q, blk_qc_t cookie, unsigned int flags);
+int bio_poll(struct bio *bio, unsigned int flags);
+int iocb_bio_iopoll(struct kiocb *kiocb, unsigned int flags);
 
 static inline struct request_queue *bdev_get_queue(struct block_device *bdev)
 {
@@ -1856,7 +1858,7 @@ static inline void blk_ksm_unregister(struct request_queue *q) { }
 
 
 struct block_device_operations {
-	blk_qc_t (*submit_bio) (struct bio *bio);
+	void (*submit_bio)(struct bio *bio);
 	int (*open) (struct block_device *, fmode_t);
 	void (*release) (struct gendisk *, fmode_t);
 	int (*rw_page)(struct block_device *, sector_t, struct page *, unsigned int);
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 483fb557d92f..876ec2b11a7d 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -332,11 +332,7 @@ struct kiocb {
 	int			ki_flags;
 	u16			ki_hint;
 	u16			ki_ioprio; /* See linux/ioprio.h */
-	union {
-		unsigned int		ki_cookie; /* for ->iopoll */
-		struct wait_page_queue	*ki_waitq; /* for async buffered IO */
-	};
-
+	struct wait_page_queue	*ki_waitq; /* for async buffered IO */
 	randomized_struct_fields_end
 };
 
diff --git a/include/linux/iomap.h b/include/linux/iomap.h
index 56e5949ccb60..ac825a498816 100644
--- a/include/linux/iomap.h
+++ b/include/linux/iomap.h
@@ -251,7 +251,7 @@ int iomap_writepages(struct address_space *mapping,
 struct iomap_dio_ops {
 	int (*end_io)(struct kiocb *iocb, ssize_t size, int error,
 		      unsigned flags);
-	blk_qc_t (*submit_io)(struct inode *inode, struct iomap *iomap,
+	void (*submit_io)(struct inode *inode, struct iomap *iomap,
 			struct bio *bio, loff_t file_offset);
 };
 
@@ -275,7 +275,6 @@ struct iomap_dio *__iomap_dio_rw(struct kiocb *iocb, struct iov_iter *iter,
 		const struct iomap_ops *ops, const struct iomap_dio_ops *dops,
 		unsigned int dio_flags);
 ssize_t iomap_dio_complete(struct iomap_dio *dio);
-int iomap_dio_iopoll(struct kiocb *kiocb, unsigned int flags);
 
 #ifdef CONFIG_SWAP
 struct file;
diff --git a/mm/page_io.c b/mm/page_io.c
index ed2eded74f3a..a68faab5b310 100644
--- a/mm/page_io.c
+++ b/mm/page_io.c
@@ -358,8 +358,6 @@ int swap_readpage(struct page *page, bool synchronous)
 	struct bio *bio;
 	int ret = 0;
 	struct swap_info_struct *sis = page_swap_info(page);
-	blk_qc_t qc;
-	struct gendisk *disk;
 	unsigned long pflags;
 
 	VM_BUG_ON_PAGE(!PageSwapCache(page) && !synchronous, page);
@@ -409,8 +407,6 @@ int swap_readpage(struct page *page, bool synchronous)
 	bio->bi_iter.bi_sector = swap_page_sector(page);
 	bio->bi_end_io = end_swap_bio_read;
 	bio_add_page(bio, page, thp_size(page), 0);
-
-	disk = bio->bi_bdev->bd_disk;
 	/*
 	 * Keep this task valid during swap readpage because the oom killer may
 	 * attempt to access it in the page fault retry time check.
@@ -422,13 +418,13 @@ int swap_readpage(struct page *page, bool synchronous)
 	}
 	count_vm_event(PSWPIN);
 	bio_get(bio);
-	qc = submit_bio(bio);
+	submit_bio(bio);
 	while (synchronous) {
 		set_current_state(TASK_UNINTERRUPTIBLE);
 		if (!READ_ONCE(bio->bi_private))
 			break;
 
-		if (!blk_poll(disk->queue, qc, 0))
+		if (!bio_poll(bio, 0))
 			blk_io_schedule();
 	}
 	__set_current_state(TASK_RUNNING);
-- 
2.30.2


^ permalink raw reply	[flat|nested] 40+ messages in thread

* [PATCH 13/15] block: don't allow writing to the poll queue attribute
  2021-05-12 13:15 switch block layer polling to a bio based model v3 Christoph Hellwig
                   ` (11 preceding siblings ...)
  2021-05-12 13:15 ` [PATCH 12/15] block: switch polling to be bio based Christoph Hellwig
@ 2021-05-12 13:15 ` Christoph Hellwig
  2021-05-12 22:04   ` Sagi Grimberg
  2021-05-12 13:15 ` [PATCH 14/15] nvme-multipath: set QUEUE_FLAG_NOWAIT Christoph Hellwig
                   ` (2 subsequent siblings)
  15 siblings, 1 reply; 40+ messages in thread
From: Christoph Hellwig @ 2021-05-12 13:15 UTC (permalink / raw)
  To: Jens Axboe
  Cc: Jeffle Xu, Ming Lei, Damien Le Moal, Keith Busch, Sagi Grimberg,
	Wunderlich, Mark, Vasudevan, Anil, linux-block, linux-fsdevel,
	linux-nvme

The poll attribute is a historic artefact from before when we had
explicit poll queues that require driver specific configuration.
Just print a warning when writing to the attribute.

Signed-off-by: Christoph Hellwig <hch@lst.de>
---
 block/blk-sysfs.c | 23 ++++-------------------
 1 file changed, 4 insertions(+), 19 deletions(-)

diff --git a/block/blk-sysfs.c b/block/blk-sysfs.c
index f89e2fc3963b..f78e73ca6091 100644
--- a/block/blk-sysfs.c
+++ b/block/blk-sysfs.c
@@ -428,26 +428,11 @@ static ssize_t queue_poll_show(struct request_queue *q, char *page)
 static ssize_t queue_poll_store(struct request_queue *q, const char *page,
 				size_t count)
 {
-	unsigned long poll_on;
-	ssize_t ret;
-
-	if (!q->tag_set || q->tag_set->nr_maps <= HCTX_TYPE_POLL ||
-	    !q->tag_set->map[HCTX_TYPE_POLL].nr_queues)
+	if (!test_bit(QUEUE_FLAG_POLL, &q->queue_flags))
 		return -EINVAL;
-
-	ret = queue_var_store(&poll_on, page, count);
-	if (ret < 0)
-		return ret;
-
-	if (poll_on) {
-		blk_queue_flag_set(QUEUE_FLAG_POLL, q);
-	} else {
-		blk_mq_freeze_queue(q);
-		blk_queue_flag_clear(QUEUE_FLAG_POLL, q);
-		blk_mq_unfreeze_queue(q);
-	}
-
-	return ret;
+	pr_info_ratelimited("writes to the poll attribute are ignored.\n");
+	pr_info_ratelimited("please use driver specific parameters instead.\n");
+	return count;
 }
 
 static ssize_t queue_io_timeout_show(struct request_queue *q, char *page)
-- 
2.30.2


^ permalink raw reply	[flat|nested] 40+ messages in thread

* [PATCH 14/15] nvme-multipath: set QUEUE_FLAG_NOWAIT
  2021-05-12 13:15 switch block layer polling to a bio based model v3 Christoph Hellwig
                   ` (12 preceding siblings ...)
  2021-05-12 13:15 ` [PATCH 13/15] block: don't allow writing to the poll queue attribute Christoph Hellwig
@ 2021-05-12 13:15 ` Christoph Hellwig
  2021-05-12 13:15 ` [PATCH 15/15] nvme-multipath: enable polled I/O Christoph Hellwig
  2021-05-13 23:33 ` switch block layer polling to a bio based model v3 Wunderlich, Mark
  15 siblings, 0 replies; 40+ messages in thread
From: Christoph Hellwig @ 2021-05-12 13:15 UTC (permalink / raw)
  To: Jens Axboe
  Cc: Jeffle Xu, Ming Lei, Damien Le Moal, Keith Busch, Sagi Grimberg,
	Wunderlich, Mark, Vasudevan, Anil, linux-block, linux-fsdevel,
	linux-nvme

The nvme multipathing code just dispatches bios to one of the blk-mq
based paths and never blocks on its own, so set QUEUE_FLAG_NOWAIT
to support REQ_NOWAIT bios.

Signed-off-by: Christoph Hellwig <hch@lst.de>
---
 drivers/nvme/host/multipath.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/nvme/host/multipath.c b/drivers/nvme/host/multipath.c
index 74455960337b..516fe977606d 100644
--- a/drivers/nvme/host/multipath.c
+++ b/drivers/nvme/host/multipath.c
@@ -445,6 +445,8 @@ int nvme_mpath_alloc_disk(struct nvme_ctrl *ctrl, struct nvme_ns_head *head)
 	if (!q)
 		goto out;
 	blk_queue_flag_set(QUEUE_FLAG_NONROT, q);
+	blk_queue_flag_set(QUEUE_FLAG_NOWAIT, q);
+
 	/* set to a default value for 512 until disk is validated */
 	blk_queue_logical_block_size(q, 512);
 	blk_set_stacking_limits(&q->limits);
-- 
2.30.2


^ permalink raw reply	[flat|nested] 40+ messages in thread

* [PATCH 15/15] nvme-multipath: enable polled I/O
  2021-05-12 13:15 switch block layer polling to a bio based model v3 Christoph Hellwig
                   ` (13 preceding siblings ...)
  2021-05-12 13:15 ` [PATCH 14/15] nvme-multipath: set QUEUE_FLAG_NOWAIT Christoph Hellwig
@ 2021-05-12 13:15 ` Christoph Hellwig
  2021-05-12 22:10   ` Sagi Grimberg
  2021-05-13 23:33 ` switch block layer polling to a bio based model v3 Wunderlich, Mark
  15 siblings, 1 reply; 40+ messages in thread
From: Christoph Hellwig @ 2021-05-12 13:15 UTC (permalink / raw)
  To: Jens Axboe
  Cc: Jeffle Xu, Ming Lei, Damien Le Moal, Keith Busch, Sagi Grimberg,
	Wunderlich, Mark, Vasudevan, Anil, linux-block, linux-fsdevel,
	linux-nvme

Set the poll queue flag to enable polling, given that the multipath
node just dispatches the bios to a lower queue.

Signed-off-by: Christoph Hellwig <hch@lst.de>
---
 drivers/nvme/host/multipath.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/drivers/nvme/host/multipath.c b/drivers/nvme/host/multipath.c
index 516fe977606d..e95b93655d06 100644
--- a/drivers/nvme/host/multipath.c
+++ b/drivers/nvme/host/multipath.c
@@ -446,6 +446,15 @@ int nvme_mpath_alloc_disk(struct nvme_ctrl *ctrl, struct nvme_ns_head *head)
 		goto out;
 	blk_queue_flag_set(QUEUE_FLAG_NONROT, q);
 	blk_queue_flag_set(QUEUE_FLAG_NOWAIT, q);
+	/*
+	 * This assumes all controllers that refer to a namespace either
+	 * support poll queues or not.  That is not a strict guarantee,
+	 * but if the assumption is wrong the effect is only suboptimal
+	 * performance but not correctness problem.
+	 */
+	if (ctrl->tagset->nr_maps > HCTX_TYPE_POLL &&
+	    ctrl->tagset->map[HCTX_TYPE_POLL].nr_queues)
+		blk_queue_flag_set(QUEUE_FLAG_POLL, q);
 
 	/* set to a default value for 512 until disk is validated */
 	blk_queue_logical_block_size(q, 512);
-- 
2.30.2


^ permalink raw reply	[flat|nested] 40+ messages in thread

* Re: [PATCH 02/15] block: don't try to poll multi-bio I/Os in __blkdev_direct_IO
  2021-05-12 13:15 ` [PATCH 02/15] block: don't try to poll multi-bio I/Os in __blkdev_direct_IO Christoph Hellwig
@ 2021-05-12 20:54   ` Sagi Grimberg
  2021-05-16 18:01   ` Kanchan Joshi
  1 sibling, 0 replies; 40+ messages in thread
From: Sagi Grimberg @ 2021-05-12 20:54 UTC (permalink / raw)
  To: Christoph Hellwig, Jens Axboe
  Cc: Jeffle Xu, Ming Lei, Damien Le Moal, Keith Busch, Wunderlich,
	Mark, Vasudevan, Anil, linux-block, linux-fsdevel, linux-nvme

Reviewed-by: Sagi Grimberg <sagi@grimberg.me>

^ permalink raw reply	[flat|nested] 40+ messages in thread

* Re: [PATCH 04/15] blk-mq: factor out a blk_qc_to_hctx helper
  2021-05-12 13:15 ` [PATCH 04/15] blk-mq: factor out a blk_qc_to_hctx helper Christoph Hellwig
@ 2021-05-12 20:58   ` Sagi Grimberg
  0 siblings, 0 replies; 40+ messages in thread
From: Sagi Grimberg @ 2021-05-12 20:58 UTC (permalink / raw)
  To: Christoph Hellwig, Jens Axboe
  Cc: Jeffle Xu, Ming Lei, Damien Le Moal, Keith Busch, Wunderlich,
	Mark, Vasudevan, Anil, linux-block, linux-fsdevel, linux-nvme

Reviewed-by: Sagi Grimberg <sagi@grimberg.me>

^ permalink raw reply	[flat|nested] 40+ messages in thread

* Re: [PATCH 05/15] blk-mq: factor out a "classic" poll helper
  2021-05-12 13:15 ` [PATCH 05/15] blk-mq: factor out a "classic" poll helper Christoph Hellwig
@ 2021-05-12 20:59   ` Sagi Grimberg
  0 siblings, 0 replies; 40+ messages in thread
From: Sagi Grimberg @ 2021-05-12 20:59 UTC (permalink / raw)
  To: Christoph Hellwig, Jens Axboe
  Cc: Jeffle Xu, Ming Lei, Damien Le Moal, Keith Busch, Wunderlich,
	Mark, Vasudevan, Anil, linux-block, linux-fsdevel, linux-nvme

A bit convoluted diff, but looks ok,

Reviewed-by: Sagi Grimberg <sagi@grimberg.me>

^ permalink raw reply	[flat|nested] 40+ messages in thread

* Re: [PATCH 03/15] iomap: don't try to poll multi-bio I/Os in __iomap_dio_rw
  2021-05-12 13:15 ` [PATCH 03/15] iomap: don't try to poll multi-bio I/Os in __iomap_dio_rw Christoph Hellwig
@ 2021-05-12 21:32   ` Darrick J. Wong
  0 siblings, 0 replies; 40+ messages in thread
From: Darrick J. Wong @ 2021-05-12 21:32 UTC (permalink / raw)
  To: Christoph Hellwig
  Cc: Jens Axboe, Jeffle Xu, Ming Lei, Damien Le Moal, Keith Busch,
	Sagi Grimberg, Wunderlich, Mark, Vasudevan, Anil, linux-block,
	linux-fsdevel, linux-nvme

On Wed, May 12, 2021 at 03:15:33PM +0200, Christoph Hellwig wrote:
> If an iocb is split into multiple bios we can't poll for both.  So don't
> bother to even try to poll in that case.
> 
> Signed-off-by: Christoph Hellwig <hch@lst.de>

Ahh the fun of reviewing things like iopoll that I'm not all /that/
familiar with...

> ---
>  fs/iomap/direct-io.c | 17 +++++++++++++++++
>  1 file changed, 17 insertions(+)
> 
> diff --git a/fs/iomap/direct-io.c b/fs/iomap/direct-io.c
> index 9398b8c31323..d5637f467109 100644
> --- a/fs/iomap/direct-io.c
> +++ b/fs/iomap/direct-io.c
> @@ -282,6 +282,13 @@ iomap_dio_bio_actor(struct inode *inode, loff_t pos, loff_t length,
>  	if (!iov_iter_count(dio->submit.iter))
>  		goto out;
>  
> +	/*
> +	 * We can only poll for single bio I/Os.
> +	 */
> +	if (need_zeroout ||
> +	    ((dio->flags & IOMAP_DIO_WRITE) && pos >= i_size_read(inode)))

Hm, is this logic here to catch the second iomap_dio_zero below the
zero_tail: label?  What happens if we have an unaligned direct write
that starts below EOF but (for whatever reason) ends the loop with pos
now above EOF but not on a block boundary?

> +		dio->iocb->ki_flags &= ~IOCB_HIPRI;
> +
>  	if (need_zeroout) {
>  		/* zero out from the start of the block to the write offset */
>  		pad = pos & (fs_block_size - 1);
> @@ -339,6 +346,11 @@ iomap_dio_bio_actor(struct inode *inode, loff_t pos, loff_t length,
>  
>  		nr_pages = bio_iov_vecs_to_alloc(dio->submit.iter,
>  						 BIO_MAX_VECS);
> +		/*
> +		 * We can only poll for single bio I/Os.
> +		 */
> +		if (nr_pages)
> +			dio->iocb->ki_flags &= ~IOCB_HIPRI;
>  		iomap_dio_submit_bio(dio, iomap, bio, pos);
>  		pos += n;
>  	} while (nr_pages);
> @@ -579,6 +591,11 @@ __iomap_dio_rw(struct kiocb *iocb, struct iov_iter *iter,
>  			iov_iter_revert(iter, pos - dio->i_size);
>  			break;
>  		}
> +
> +		/*
> +		 * We can only poll for single bio I/Os.
> +		 */
> +		iocb->ki_flags &= ~IOCB_HIPRI;

Hmm, why is this here?  Won't this clear IOCB_HIPRI even if the first
iomap_apply call successfully creates a polled bio for the entire iovec
such that we exit the loop one line later because count becomes zero?
How does the upper layer (io_uring, I surmise?) know that there's
a bio that it should poll for?

<shrug> Unless the only effect that this has is making it so that the
subsequent calls to iomap_apply don't have the polling mode set?  I see
enough places in io_uring.c that check (iocb->ki_flags & IOCB_HIPRI) to
make me wonder if the lifetime of that flag ends as soon as we get to
->{read,write}_iter?

--D

>  	} while ((count = iov_iter_count(iter)) > 0);
>  	blk_finish_plug(&plug);
>  
> -- 
> 2.30.2
> 

^ permalink raw reply	[flat|nested] 40+ messages in thread

* Re: [PATCH 06/15] blk-mq: remove blk_qc_t_to_tag and blk_qc_t_is_internal
  2021-05-12 13:15 ` [PATCH 06/15] blk-mq: remove blk_qc_t_to_tag and blk_qc_t_is_internal Christoph Hellwig
@ 2021-05-12 21:42   ` Sagi Grimberg
  0 siblings, 0 replies; 40+ messages in thread
From: Sagi Grimberg @ 2021-05-12 21:42 UTC (permalink / raw)
  To: Christoph Hellwig, Jens Axboe
  Cc: Jeffle Xu, Ming Lei, Damien Le Moal, Keith Busch, Wunderlich,
	Mark, Vasudevan, Anil, linux-block, linux-fsdevel, linux-nvme

Reviewed-by: Sagi Grimberg <sagi@grimberg.me>

^ permalink raw reply	[flat|nested] 40+ messages in thread

* Re: [PATCH 07/15] blk-mq: remove blk_qc_t_valid
  2021-05-12 13:15 ` [PATCH 07/15] blk-mq: remove blk_qc_t_valid Christoph Hellwig
@ 2021-05-12 21:43   ` Sagi Grimberg
  0 siblings, 0 replies; 40+ messages in thread
From: Sagi Grimberg @ 2021-05-12 21:43 UTC (permalink / raw)
  To: Christoph Hellwig, Jens Axboe
  Cc: Jeffle Xu, Ming Lei, Damien Le Moal, Keith Busch, Wunderlich,
	Mark, Vasudevan, Anil, linux-block, linux-fsdevel, linux-nvme

Reviewed-by: Sagi Grimberg <sagi@grimberg.me>

^ permalink raw reply	[flat|nested] 40+ messages in thread

* Re: [PATCH 08/15] io_uring: don't sleep when polling for I/O
  2021-05-12 13:15 ` [PATCH 08/15] io_uring: don't sleep when polling for I/O Christoph Hellwig
@ 2021-05-12 21:55   ` Sagi Grimberg
  2021-05-19 13:02     ` Christoph Hellwig
  0 siblings, 1 reply; 40+ messages in thread
From: Sagi Grimberg @ 2021-05-12 21:55 UTC (permalink / raw)
  To: Christoph Hellwig, Jens Axboe
  Cc: Jeffle Xu, Ming Lei, Damien Le Moal, Keith Busch, Wunderlich,
	Mark, Vasudevan, Anil, linux-block, linux-fsdevel, linux-nvme



On 5/12/21 6:15 AM, Christoph Hellwig wrote:
> There is no point in sleeping for the expected I/O completion timeout
> in the io_uring async polling model as we never poll for a specific
> I/O.  Split the boolean spin argument to blk_poll into a set of flags
> to control sleeping and the oneshot behavior separately.
> 
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> ---
>   block/blk-mq.c           | 18 ++++++++----------
>   drivers/nvme/host/core.c |  2 +-
>   fs/block_dev.c           |  8 ++++----
>   fs/io_uring.c            | 14 +++++++-------
>   fs/iomap/direct-io.c     |  6 +++---
>   include/linux/blkdev.h   |  6 +++++-
>   include/linux/fs.h       |  2 +-
>   include/linux/iomap.h    |  2 +-
>   mm/page_io.c             |  2 +-
>   9 files changed, 31 insertions(+), 29 deletions(-)
> 
> diff --git a/block/blk-mq.c b/block/blk-mq.c
> index ac0b517c5503..164e39d34bf6 100644
> --- a/block/blk-mq.c
> +++ b/block/blk-mq.c
> @@ -3873,7 +3873,7 @@ static bool blk_mq_poll_hybrid(struct request_queue *q, blk_qc_t qc)
>   }
>   
>   static int blk_mq_poll_classic(struct request_queue *q, blk_qc_t cookie,
> -		bool spin)
> +		unsigned int flags)
>   {
>   	struct blk_mq_hw_ctx *hctx = blk_qc_to_hctx(q, cookie);
>   	long state = current->state;
> @@ -3896,7 +3896,7 @@ static int blk_mq_poll_classic(struct request_queue *q, blk_qc_t cookie,
>   		if (current->state == TASK_RUNNING)
>   			return 1;
>   
> -		if (ret < 0 || !spin)
> +		if (ret < 0 || (flags & BLK_POLL_ONESHOT))
>   			break;
>   		cpu_relax();
>   	} while (!need_resched());
> @@ -3909,15 +3909,13 @@ static int blk_mq_poll_classic(struct request_queue *q, blk_qc_t cookie,
>    * blk_poll - poll for IO completions
>    * @q:  the queue
>    * @cookie: cookie passed back at IO submission time
> - * @spin: whether to spin for completions
> + * @flags: BLK_POLL_* flags that control the behavior
>    *
>    * Description:
>    *    Poll for completions on the passed in queue. Returns number of
> - *    completed entries found. If @spin is true, then blk_poll will continue
> - *    looping until at least one completion is found, unless the task is
> - *    otherwise marked running (or we need to reschedule).
> + *    completed entries found.
>    */
> -int blk_poll(struct request_queue *q, blk_qc_t cookie, bool spin)
> +int blk_poll(struct request_queue *q, blk_qc_t cookie, unsigned int flags)
>   {
>   	if (cookie == BLK_QC_T_NONE ||
>   	    !test_bit(QUEUE_FLAG_POLL, &q->queue_flags))
> @@ -3926,12 +3924,12 @@ int blk_poll(struct request_queue *q, blk_qc_t cookie, bool spin)
>   	if (current->plug)
>   		blk_flush_plug_list(current->plug, false);
>   
> -	/* If specified not to spin, we also should not sleep. */
> -	if (spin && q->poll_nsec != BLK_MQ_POLL_CLASSIC) {
> +	if (!(flags & BLK_POLL_NOSLEEP) &&
> +	    q->poll_nsec != BLK_MQ_POLL_CLASSIC) {
>   		if (blk_mq_poll_hybrid(q, cookie))
>   			return 1;
>   	}
> -	return blk_mq_poll_classic(q, cookie, spin);
> +	return blk_mq_poll_classic(q, cookie, flags);

I think that the combination of oneshot and nosleep flags to replace
a boolen spin is a little hard to follow (especially that spin doesn't
mean spinning without sleeping).

Maybe we should break it to:
1. replace spin to flags with ONESHOT passed from io_uring (direct
    replacement)
2. add NOSLEEP passed from io_uring as there is no need for it.

Just a suggestion though that would help (me at least) to follow
this more easily.

^ permalink raw reply	[flat|nested] 40+ messages in thread

* Re: [PATCH 09/15] block: rename REQ_HIPRI to REQ_POLLED
  2021-05-12 13:15 ` [PATCH 09/15] block: rename REQ_HIPRI to REQ_POLLED Christoph Hellwig
@ 2021-05-12 21:56   ` Sagi Grimberg
  2021-05-12 22:43   ` Chaitanya Kulkarni
  1 sibling, 0 replies; 40+ messages in thread
From: Sagi Grimberg @ 2021-05-12 21:56 UTC (permalink / raw)
  To: Christoph Hellwig, Jens Axboe
  Cc: Jeffle Xu, Ming Lei, Damien Le Moal, Keith Busch, Wunderlich,
	Mark, Vasudevan, Anil, linux-block, linux-fsdevel, linux-nvme

Reviewed-by: Sagi Grimberg <sagi@grimberg.me>

^ permalink raw reply	[flat|nested] 40+ messages in thread

* Re: [PATCH 11/15] block: define 'struct bvec_iter' as packed
  2021-05-12 13:15 ` [PATCH 11/15] block: define 'struct bvec_iter' as packed Christoph Hellwig
@ 2021-05-12 21:58   ` Sagi Grimberg
  0 siblings, 0 replies; 40+ messages in thread
From: Sagi Grimberg @ 2021-05-12 21:58 UTC (permalink / raw)
  To: Christoph Hellwig, Jens Axboe
  Cc: Jeffle Xu, Ming Lei, Damien Le Moal, Keith Busch, Wunderlich,
	Mark, Vasudevan, Anil, linux-block, linux-fsdevel, linux-nvme,
	Hannes Reinecke

Reviewed-by: Sagi Grimberg <sagi@grimberg.me>

^ permalink raw reply	[flat|nested] 40+ messages in thread

* Re: [PATCH 12/15] block: switch polling to be bio based
  2021-05-12 13:15 ` [PATCH 12/15] block: switch polling to be bio based Christoph Hellwig
@ 2021-05-12 22:03   ` Sagi Grimberg
  2021-05-12 22:12     ` Keith Busch
  2021-05-13  1:26     ` Ming Lei
  2021-05-13  1:23   ` Ming Lei
  1 sibling, 2 replies; 40+ messages in thread
From: Sagi Grimberg @ 2021-05-12 22:03 UTC (permalink / raw)
  To: Christoph Hellwig, Jens Axboe
  Cc: Jeffle Xu, Ming Lei, Damien Le Moal, Keith Busch, Wunderlich,
	Mark, Vasudevan, Anil, linux-block, linux-fsdevel, linux-nvme



On 5/12/21 6:15 AM, Christoph Hellwig wrote:
> Replace the blk_poll interface that requires the caller to keep a queue
> and cookie from the submissions with polling based on the bio.
> 
> Polling for the bio itself leads to a few advantages:
> 
>   - the cookie construction can made entirely private in blk-mq.c
>   - the caller does not need to remember the request_queue and cookie
>     separately and thus sidesteps their lifetime issues
>   - keeping the device and the cookie inside the bio allows to trivially
>     support polling BIOs remapping by stacking drivers
>   - a lot of code to propagate the cookie back up the submission path can
>     be removed entirely.
> 
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> ---
>   arch/m68k/emu/nfblock.c             |   3 +-
>   arch/xtensa/platforms/iss/simdisk.c |   3 +-
>   block/bio.c                         |   1 +
>   block/blk-core.c                    | 120 +++++++++++++++++++++-------
>   block/blk-mq.c                      |  73 ++++++-----------
>   block/blk-mq.h                      |   2 +
>   drivers/block/brd.c                 |  12 ++-
>   drivers/block/drbd/drbd_int.h       |   2 +-
>   drivers/block/drbd/drbd_req.c       |   3 +-
>   drivers/block/n64cart.c             |  12 ++-
>   drivers/block/null_blk/main.c       |   3 +-
>   drivers/block/pktcdvd.c             |   7 +-
>   drivers/block/ps3vram.c             |   6 +-
>   drivers/block/rsxx/dev.c            |   7 +-
>   drivers/block/zram/zram_drv.c       |  10 +--
>   drivers/lightnvm/pblk-init.c        |   6 +-
>   drivers/md/bcache/request.c         |  13 ++-
>   drivers/md/bcache/request.h         |   4 +-
>   drivers/md/dm.c                     |  28 +++----
>   drivers/md/md.c                     |  10 +--
>   drivers/nvdimm/blk.c                |   5 +-
>   drivers/nvdimm/btt.c                |   5 +-
>   drivers/nvdimm/pmem.c               |   3 +-
>   drivers/nvme/host/core.c            |   2 +-
>   drivers/nvme/host/multipath.c       |   6 +-
>   drivers/s390/block/dcssblk.c        |   7 +-
>   drivers/s390/block/xpram.c          |   5 +-
>   fs/block_dev.c                      |  25 ++----
>   fs/btrfs/inode.c                    |   8 +-
>   fs/ext4/file.c                      |   2 +-
>   fs/gfs2/file.c                      |   4 +-
>   fs/iomap/direct-io.c                |  39 +++------
>   fs/xfs/xfs_file.c                   |   2 +-
>   fs/zonefs/super.c                   |   2 +-
>   include/linux/bio.h                 |   2 +-
>   include/linux/blk-mq.h              |  15 +---
>   include/linux/blk_types.h           |  12 ++-
>   include/linux/blkdev.h              |   8 +-
>   include/linux/fs.h                  |   6 +-
>   include/linux/iomap.h               |   3 +-
>   mm/page_io.c                        |   8 +-
>   41 files changed, 223 insertions(+), 271 deletions(-)
> 
> diff --git a/arch/m68k/emu/nfblock.c b/arch/m68k/emu/nfblock.c
> index ba808543161a..dd36808f0d5e 100644
> --- a/arch/m68k/emu/nfblock.c
> +++ b/arch/m68k/emu/nfblock.c
> @@ -59,7 +59,7 @@ struct nfhd_device {
>   	struct gendisk *disk;
>   };
>   
> -static blk_qc_t nfhd_submit_bio(struct bio *bio)
> +static void nfhd_submit_bio(struct bio *bio)
>   {
>   	struct nfhd_device *dev = bio->bi_bdev->bd_disk->private_data;
>   	struct bio_vec bvec;
> @@ -77,7 +77,6 @@ static blk_qc_t nfhd_submit_bio(struct bio *bio)
>   		sec += len;
>   	}
>   	bio_endio(bio);
> -	return BLK_QC_T_NONE;
>   }
>   
>   static int nfhd_getgeo(struct block_device *bdev, struct hd_geometry *geo)
> diff --git a/arch/xtensa/platforms/iss/simdisk.c b/arch/xtensa/platforms/iss/simdisk.c
> index fc09be7b1347..182825d639e2 100644
> --- a/arch/xtensa/platforms/iss/simdisk.c
> +++ b/arch/xtensa/platforms/iss/simdisk.c
> @@ -101,7 +101,7 @@ static void simdisk_transfer(struct simdisk *dev, unsigned long sector,
>   	spin_unlock(&dev->lock);
>   }
>   
> -static blk_qc_t simdisk_submit_bio(struct bio *bio)
> +static void simdisk_submit_bio(struct bio *bio)
>   {
>   	struct simdisk *dev = bio->bi_bdev->bd_disk->private_data;
>   	struct bio_vec bvec;
> @@ -119,7 +119,6 @@ static blk_qc_t simdisk_submit_bio(struct bio *bio)
>   	}
>   
>   	bio_endio(bio);
> -	return BLK_QC_T_NONE;
>   }
>   
>   static int simdisk_open(struct block_device *bdev, fmode_t mode)
> diff --git a/block/bio.c b/block/bio.c
> index de5505d7018e..986908cc99d4 100644
> --- a/block/bio.c
> +++ b/block/bio.c
> @@ -250,6 +250,7 @@ void bio_init(struct bio *bio, struct bio_vec *table,
>   	memset(bio, 0, sizeof(*bio));
>   	atomic_set(&bio->__bi_remaining, 1);
>   	atomic_set(&bio->__bi_cnt, 1);
> +	bio->bi_cookie = BLK_QC_T_NONE;
>   
>   	bio->bi_io_vec = table;
>   	bio->bi_max_vecs = max_vecs;
> diff --git a/block/blk-core.c b/block/blk-core.c
> index 94a817532472..c024cba98195 100644
> --- a/block/blk-core.c
> +++ b/block/blk-core.c
> @@ -910,18 +910,18 @@ static noinline_for_stack bool submit_bio_checks(struct bio *bio)
>   	return false;
>   }
>   
> -static blk_qc_t __submit_bio(struct bio *bio)
> +static void __submit_bio(struct bio *bio)
>   {
>   	struct gendisk *disk = bio->bi_bdev->bd_disk;
> -	blk_qc_t ret = BLK_QC_T_NONE;
>   
>   	if (blk_crypto_bio_prep(&bio)) {
> -		if (!disk->fops->submit_bio)
> -			return blk_mq_submit_bio(bio);
> -		ret = disk->fops->submit_bio(bio);
> +		if (!disk->fops->submit_bio) {
> +			blk_mq_submit_bio(bio);
> +			return;
> +		}
> +		disk->fops->submit_bio(bio);
>   	}
>   	blk_queue_exit(disk->queue);
> -	return ret;
>   }
>   
>   /*
> @@ -943,10 +943,9 @@ static blk_qc_t __submit_bio(struct bio *bio)
>    * bio_list_on_stack[1] contains bios that were submitted before the current
>    *	->submit_bio_bio, but that haven't been processed yet.
>    */
> -static blk_qc_t __submit_bio_noacct(struct bio *bio)
> +static void __submit_bio_noacct(struct bio *bio)
>   {
>   	struct bio_list bio_list_on_stack[2];
> -	blk_qc_t ret = BLK_QC_T_NONE;
>   
>   	BUG_ON(bio->bi_next);
>   
> @@ -966,7 +965,7 @@ static blk_qc_t __submit_bio_noacct(struct bio *bio)
>   		bio_list_on_stack[1] = bio_list_on_stack[0];
>   		bio_list_init(&bio_list_on_stack[0]);
>   
> -		ret = __submit_bio(bio);
> +		__submit_bio(bio);
>   
>   		/*
>   		 * Sort new bios into those for a lower level and those for the
> @@ -989,13 +988,11 @@ static blk_qc_t __submit_bio_noacct(struct bio *bio)
>   	} while ((bio = bio_list_pop(&bio_list_on_stack[0])));
>   
>   	current->bio_list = NULL;
> -	return ret;
>   }
>   
> -static blk_qc_t __submit_bio_noacct_mq(struct bio *bio)
> +static void __submit_bio_noacct_mq(struct bio *bio)
>   {
>   	struct bio_list bio_list[2] = { };
> -	blk_qc_t ret = BLK_QC_T_NONE;
>   
>   	current->bio_list = bio_list;
>   
> @@ -1007,15 +1004,13 @@ static blk_qc_t __submit_bio_noacct_mq(struct bio *bio)
>   
>   		if (!blk_crypto_bio_prep(&bio)) {
>   			blk_queue_exit(disk->queue);
> -			ret = BLK_QC_T_NONE;
>   			continue;
>   		}
>   
> -		ret = blk_mq_submit_bio(bio);
> +		blk_mq_submit_bio(bio);
>   	} while ((bio = bio_list_pop(&bio_list[0])));
>   
>   	current->bio_list = NULL;
> -	return ret;
>   }
>   
>   /**
> @@ -1027,10 +1022,10 @@ static blk_qc_t __submit_bio_noacct_mq(struct bio *bio)
>    * systems and other upper level users of the block layer should use
>    * submit_bio() instead.
>    */
> -blk_qc_t submit_bio_noacct(struct bio *bio)
> +void submit_bio_noacct(struct bio *bio)
>   {
>   	if (!submit_bio_checks(bio))
> -		return BLK_QC_T_NONE;
> +		return;
>   
>   	/*
>   	 * We only want one ->submit_bio to be active at a time, else stack
> @@ -1038,14 +1033,12 @@ blk_qc_t submit_bio_noacct(struct bio *bio)
>   	 * to collect a list of requests submited by a ->submit_bio method while
>   	 * it is active, and then process them after it returned.
>   	 */
> -	if (current->bio_list) {
> +	if (current->bio_list)
>   		bio_list_add(&current->bio_list[0], bio);
> -		return BLK_QC_T_NONE;
> -	}
> -
> -	if (!bio->bi_bdev->bd_disk->fops->submit_bio)
> -		return __submit_bio_noacct_mq(bio);
> -	return __submit_bio_noacct(bio);
> +	else if (!bio->bi_bdev->bd_disk->fops->submit_bio)
> +		__submit_bio_noacct_mq(bio);
> +	else
> +		__submit_bio_noacct(bio);
>   }
>   EXPORT_SYMBOL(submit_bio_noacct);
>   
> @@ -1062,10 +1055,10 @@ EXPORT_SYMBOL(submit_bio_noacct);
>    * in @bio.  The bio must NOT be touched by thecaller until ->bi_end_io() has
>    * been called.
>    */
> -blk_qc_t submit_bio(struct bio *bio)
> +void submit_bio(struct bio *bio)
>   {
>   	if (blkcg_punt_bio_submit(bio))
> -		return BLK_QC_T_NONE;
> +		return;
>   
>   	/*
>   	 * If it's a regular read/write or a barrier with data attached,
> @@ -1097,19 +1090,84 @@ blk_qc_t submit_bio(struct bio *bio)
>   	if (unlikely(bio_op(bio) == REQ_OP_READ &&
>   	    bio_flagged(bio, BIO_WORKINGSET))) {
>   		unsigned long pflags;
> -		blk_qc_t ret;
>   
>   		psi_memstall_enter(&pflags);
> -		ret = submit_bio_noacct(bio);
> +		submit_bio_noacct(bio);
>   		psi_memstall_leave(&pflags);
> -
> -		return ret;
> +		return;
>   	}
>   
> -	return submit_bio_noacct(bio);
> +	submit_bio_noacct(bio);
>   }
>   EXPORT_SYMBOL(submit_bio);
>   
> +/**
> + * bio_poll - poll for BIO completions
> + * @bio: bio to poll for
> + * @flags: BLK_POLL_* flags that control the behavior
> + *
> + * Poll for completions on queue associated with the bio. Returns number of
> + * completed entries found.
> + *
> + * Note: the caller must either be the context that submitted @bio, or
> + * be in a RCU critical section to prevent freeing of @bio.
> + */
> +int bio_poll(struct bio *bio, unsigned int flags)
> +{
> +	struct request_queue *q = bio->bi_bdev->bd_disk->queue;
> +	blk_qc_t cookie = READ_ONCE(bio->bi_cookie);
> +
> +	if (cookie == BLK_QC_T_NONE ||
> +	    !test_bit(QUEUE_FLAG_POLL, &q->queue_flags))
> +		return 0;
> +
> +	if (current->plug)
> +		blk_flush_plug_list(current->plug, false);
> +
> +	/* not yet implemented, so this should not happen */
> +	if (WARN_ON_ONCE(!queue_is_mq(q)))

What happens if the I/O wasn't (yet) queued to the bottom device
(i.e. no available path in nvme-mpath)?

In this case the disk would be the mpath device node (which is
not mq...)

^ permalink raw reply	[flat|nested] 40+ messages in thread

* Re: [PATCH 13/15] block: don't allow writing to the poll queue attribute
  2021-05-12 13:15 ` [PATCH 13/15] block: don't allow writing to the poll queue attribute Christoph Hellwig
@ 2021-05-12 22:04   ` Sagi Grimberg
  0 siblings, 0 replies; 40+ messages in thread
From: Sagi Grimberg @ 2021-05-12 22:04 UTC (permalink / raw)
  To: Christoph Hellwig, Jens Axboe
  Cc: Jeffle Xu, Ming Lei, Damien Le Moal, Keith Busch, Wunderlich,
	Mark, Vasudevan, Anil, linux-block, linux-fsdevel, linux-nvme

Reviewed-by: Sagi Grimberg <sagi@grimberg.me>

^ permalink raw reply	[flat|nested] 40+ messages in thread

* Re: [PATCH 15/15] nvme-multipath: enable polled I/O
  2021-05-12 13:15 ` [PATCH 15/15] nvme-multipath: enable polled I/O Christoph Hellwig
@ 2021-05-12 22:10   ` Sagi Grimberg
  2021-05-12 22:16     ` Keith Busch
  0 siblings, 1 reply; 40+ messages in thread
From: Sagi Grimberg @ 2021-05-12 22:10 UTC (permalink / raw)
  To: Christoph Hellwig, Jens Axboe
  Cc: Jeffle Xu, Ming Lei, Damien Le Moal, Keith Busch, Wunderlich,
	Mark, Vasudevan, Anil, linux-block, linux-fsdevel, linux-nvme


> Set the poll queue flag to enable polling, given that the multipath
> node just dispatches the bios to a lower queue.
> 
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> ---
>   drivers/nvme/host/multipath.c | 9 +++++++++
>   1 file changed, 9 insertions(+)
> 
> diff --git a/drivers/nvme/host/multipath.c b/drivers/nvme/host/multipath.c
> index 516fe977606d..e95b93655d06 100644
> --- a/drivers/nvme/host/multipath.c
> +++ b/drivers/nvme/host/multipath.c
> @@ -446,6 +446,15 @@ int nvme_mpath_alloc_disk(struct nvme_ctrl *ctrl, struct nvme_ns_head *head)
>   		goto out;
>   	blk_queue_flag_set(QUEUE_FLAG_NONROT, q);
>   	blk_queue_flag_set(QUEUE_FLAG_NOWAIT, q);
> +	/*
> +	 * This assumes all controllers that refer to a namespace either
> +	 * support poll queues or not.  That is not a strict guarantee,
> +	 * but if the assumption is wrong the effect is only suboptimal
> +	 * performance but not correctness problem.
> +	 */
> +	if (ctrl->tagset->nr_maps > HCTX_TYPE_POLL &&
> +	    ctrl->tagset->map[HCTX_TYPE_POLL].nr_queues)
> +		blk_queue_flag_set(QUEUE_FLAG_POLL, q);

If one controller does not support polling and the other does, won't
the block layer fail to map a queue for REQ_POLLED requests?

Maybe clear in the else case here?

^ permalink raw reply	[flat|nested] 40+ messages in thread

* Re: [PATCH 12/15] block: switch polling to be bio based
  2021-05-12 22:03   ` Sagi Grimberg
@ 2021-05-12 22:12     ` Keith Busch
  2021-05-14  2:50       ` Keith Busch
  2021-05-13  1:26     ` Ming Lei
  1 sibling, 1 reply; 40+ messages in thread
From: Keith Busch @ 2021-05-12 22:12 UTC (permalink / raw)
  To: Sagi Grimberg
  Cc: Christoph Hellwig, Jens Axboe, Jeffle Xu, Ming Lei,
	Damien Le Moal, Wunderlich, Mark, Vasudevan, Anil, linux-block,
	linux-fsdevel, linux-nvme

On Wed, May 12, 2021 at 03:03:40PM -0700, Sagi Grimberg wrote:
> On 5/12/21 6:15 AM, Christoph Hellwig wrote:
> > + *
> > + * Note: the caller must either be the context that submitted @bio, or
> > + * be in a RCU critical section to prevent freeing of @bio.
> > + */
> > +int bio_poll(struct bio *bio, unsigned int flags)
> > +{
> > +	struct request_queue *q = bio->bi_bdev->bd_disk->queue;
> > +	blk_qc_t cookie = READ_ONCE(bio->bi_cookie);
> > +
> > +	if (cookie == BLK_QC_T_NONE ||
> > +	    !test_bit(QUEUE_FLAG_POLL, &q->queue_flags))
> > +		return 0;
> > +
> > +	if (current->plug)
> > +		blk_flush_plug_list(current->plug, false);
> > +
> > +	/* not yet implemented, so this should not happen */
> > +	if (WARN_ON_ONCE(!queue_is_mq(q)))
> 
> What happens if the I/O wasn't (yet) queued to the bottom device
> (i.e. no available path in nvme-mpath)?
> 
> In this case the disk would be the mpath device node (which is
> not mq...)

The bi_cookie should remain BLK_QC_T_NONE in that case, so we wouldn't
get to the warning. But if that does happen, it doesn't appear that
anyone is going to wake up thread that needs to poll for this bio's
completion when a path becomes available for dispatch. I think it would
make sense for nvme-mpath to just clear the REQ_POLLED flag if it
doesn't immediately have viable path.

^ permalink raw reply	[flat|nested] 40+ messages in thread

* Re: [PATCH 15/15] nvme-multipath: enable polled I/O
  2021-05-12 22:10   ` Sagi Grimberg
@ 2021-05-12 22:16     ` Keith Busch
  0 siblings, 0 replies; 40+ messages in thread
From: Keith Busch @ 2021-05-12 22:16 UTC (permalink / raw)
  To: Sagi Grimberg
  Cc: Christoph Hellwig, Jens Axboe, Jeffle Xu, Ming Lei,
	Damien Le Moal, Wunderlich, Mark, Vasudevan, Anil, linux-block,
	linux-fsdevel, linux-nvme

On Wed, May 12, 2021 at 03:10:58PM -0700, Sagi Grimberg wrote:
> 
> > Set the poll queue flag to enable polling, given that the multipath
> > node just dispatches the bios to a lower queue.
> > 
> > Signed-off-by: Christoph Hellwig <hch@lst.de>
> > ---
> >   drivers/nvme/host/multipath.c | 9 +++++++++
> >   1 file changed, 9 insertions(+)
> > 
> > diff --git a/drivers/nvme/host/multipath.c b/drivers/nvme/host/multipath.c
> > index 516fe977606d..e95b93655d06 100644
> > --- a/drivers/nvme/host/multipath.c
> > +++ b/drivers/nvme/host/multipath.c
> > @@ -446,6 +446,15 @@ int nvme_mpath_alloc_disk(struct nvme_ctrl *ctrl, struct nvme_ns_head *head)
> >   		goto out;
> >   	blk_queue_flag_set(QUEUE_FLAG_NONROT, q);
> >   	blk_queue_flag_set(QUEUE_FLAG_NOWAIT, q);
> > +	/*
> > +	 * This assumes all controllers that refer to a namespace either
> > +	 * support poll queues or not.  That is not a strict guarantee,
> > +	 * but if the assumption is wrong the effect is only suboptimal
> > +	 * performance but not correctness problem.
> > +	 */
> > +	if (ctrl->tagset->nr_maps > HCTX_TYPE_POLL &&
> > +	    ctrl->tagset->map[HCTX_TYPE_POLL].nr_queues)
> > +		blk_queue_flag_set(QUEUE_FLAG_POLL, q);
> 
> If one controller does not support polling and the other does, won't
> the block layer fail to map a queue for REQ_POLLED requests?
> 
> Maybe clear in the else case here?

This only gets called once per head, though, so it's just going to
inherit whatever capabilities the first controller happens to have. If
we do set QUEUE_FLAG_POLL, but the chosen path happens to not support
it, then submit_bio_checks() will strip off the bio flag and it will be
processed as a non-polled request.

If the first controller can't support a polled queue, then other
controllers that do will just have unusable resources.

^ permalink raw reply	[flat|nested] 40+ messages in thread

* Re: [PATCH 09/15] block: rename REQ_HIPRI to REQ_POLLED
  2021-05-12 13:15 ` [PATCH 09/15] block: rename REQ_HIPRI to REQ_POLLED Christoph Hellwig
  2021-05-12 21:56   ` Sagi Grimberg
@ 2021-05-12 22:43   ` Chaitanya Kulkarni
  1 sibling, 0 replies; 40+ messages in thread
From: Chaitanya Kulkarni @ 2021-05-12 22:43 UTC (permalink / raw)
  To: Christoph Hellwig, Jens Axboe
  Cc: Jeffle Xu, Ming Lei, Damien Le Moal, Keith Busch, Sagi Grimberg,
	Wunderlich, Mark, Vasudevan, Anil, linux-block, linux-fsdevel,
	linux-nvme

On 5/12/21 06:16, Christoph Hellwig wrote:
> Unlike the RWF_HIPRI userspace ABI which is intentionally kept vague,
> the bio flag is specific to the polling implementation, so rename and
> document it properly.
>
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> ---

Looks good.

Reviewed-by: Chaitanya Kulkarni <chaitanya.kulkarni@wdc.com>



^ permalink raw reply	[flat|nested] 40+ messages in thread

* Re: [PATCH 12/15] block: switch polling to be bio based
  2021-05-12 13:15 ` [PATCH 12/15] block: switch polling to be bio based Christoph Hellwig
  2021-05-12 22:03   ` Sagi Grimberg
@ 2021-05-13  1:23   ` Ming Lei
  1 sibling, 0 replies; 40+ messages in thread
From: Ming Lei @ 2021-05-13  1:23 UTC (permalink / raw)
  To: Christoph Hellwig
  Cc: Jens Axboe, Jeffle Xu, Damien Le Moal, Keith Busch,
	Sagi Grimberg, Wunderlich, Mark, Vasudevan, Anil, linux-block,
	linux-fsdevel, linux-nvme

On Wed, May 12, 2021 at 03:15:42PM +0200, Christoph Hellwig wrote:
> Replace the blk_poll interface that requires the caller to keep a queue
> and cookie from the submissions with polling based on the bio.
> 
> Polling for the bio itself leads to a few advantages:
> 
>  - the cookie construction can made entirely private in blk-mq.c
>  - the caller does not need to remember the request_queue and cookie
>    separately and thus sidesteps their lifetime issues
>  - keeping the device and the cookie inside the bio allows to trivially
>    support polling BIOs remapping by stacking drivers
>  - a lot of code to propagate the cookie back up the submission path can
>    be removed entirely.
> 
> Signed-off-by: Christoph Hellwig <hch@lst.de>

...

> +
> +/*
> + * Helper to implement file_operations.iopoll.  Requires the bio to be stored
> + * in iocb->private, and cleared before freeing the bio.
> + */
> +int iocb_bio_iopoll(struct kiocb *kiocb, unsigned int flags)
> +{
> +	struct bio *bio;
> +	int ret = 0;
> +
> +	/*
> +	 * Note: the bio cache only uses SLAB_TYPESAFE_BY_RCU, so bio can
> +	 * point to a freshly allocated bio at this point.  If that happens
> +	 * we have a few cases to consider:
> +	 *
> +	 *  1) the bio is beeing initialized and bi_bdev is NULL.  We can just
> +	 *     simply nothing in this case
> +	 *  2) the bio points to a not poll enabled device.  bio_poll will catch
> +	 *     this and return 0
> +	 *  3) the bio points to a poll capable device, including but not
> +	 *     limited to the one that the original bio pointed to.  In this
> +	 *     case we will call into the actual poll method and poll for I/O,
> +	 *     even if we don't need to, but it won't cause harm either.
> +	 *
> +	 * For cases 2) and 3) above the RCU grace period ensures that the
> +	 * bi_bdev is still allocated, and because partitions hold a reference
> +	 * to the whole device bdev and thus disk it is still valid.
> +	 */
> +	rcu_read_lock();
> +	bio = READ_ONCE(kiocb->private);
> +	if (bio && bio->bi_bdev)
> +		ret = bio_poll(bio, flags);

The bio can be re-allocated from another IO path & bdev after checking on
bio->bi_bdev in the above code, then this bio is freed, its ->bi_bdev is freed,
same with its associated disk/hw queues/request queue.

Both bdev and request queue are freed via rcu, but disk/hw queues are freed
immediately, so there is still UAF risk in bio_poll().

Thanks, 
Ming


^ permalink raw reply	[flat|nested] 40+ messages in thread

* Re: [PATCH 12/15] block: switch polling to be bio based
  2021-05-12 22:03   ` Sagi Grimberg
  2021-05-12 22:12     ` Keith Busch
@ 2021-05-13  1:26     ` Ming Lei
  1 sibling, 0 replies; 40+ messages in thread
From: Ming Lei @ 2021-05-13  1:26 UTC (permalink / raw)
  To: Sagi Grimberg
  Cc: Christoph Hellwig, Jens Axboe, Jeffle Xu, Damien Le Moal,
	Keith Busch, Wunderlich, Mark, Vasudevan, Anil, linux-block,
	linux-fsdevel, linux-nvme

On Wed, May 12, 2021 at 03:03:40PM -0700, Sagi Grimberg wrote:
> 
> 
> On 5/12/21 6:15 AM, Christoph Hellwig wrote:
> > Replace the blk_poll interface that requires the caller to keep a queue
> > and cookie from the submissions with polling based on the bio.
> > 
> > Polling for the bio itself leads to a few advantages:
> > 
> >   - the cookie construction can made entirely private in blk-mq.c
> >   - the caller does not need to remember the request_queue and cookie
> >     separately and thus sidesteps their lifetime issues
> >   - keeping the device and the cookie inside the bio allows to trivially
> >     support polling BIOs remapping by stacking drivers
> >   - a lot of code to propagate the cookie back up the submission path can
> >     be removed entirely.
> > 
> > Signed-off-by: Christoph Hellwig <hch@lst.de>

...

> > +int bio_poll(struct bio *bio, unsigned int flags)
> > +{
> > +	struct request_queue *q = bio->bi_bdev->bd_disk->queue;
> > +	blk_qc_t cookie = READ_ONCE(bio->bi_cookie);
> > +
> > +	if (cookie == BLK_QC_T_NONE ||
> > +	    !test_bit(QUEUE_FLAG_POLL, &q->queue_flags))
> > +		return 0;
> > +
> > +	if (current->plug)
> > +		blk_flush_plug_list(current->plug, false);
> > +
> > +	/* not yet implemented, so this should not happen */
> > +	if (WARN_ON_ONCE(!queue_is_mq(q)))
> 
> What happens if the I/O wasn't (yet) queued to the bottom device
> (i.e. no available path in nvme-mpath)?
> 
> In this case the disk would be the mpath device node (which is
> not mq...)

->bi_cookie is only set in blk_mq_start_request() for blk-mq request,
if the I/O isn't queued to bottom device, it won't be polled because
->bi_cookie is still BLK_QC_T_NONE.


Thanks,
Ming


^ permalink raw reply	[flat|nested] 40+ messages in thread

* RE: switch block layer polling to a bio based model v3
  2021-05-12 13:15 switch block layer polling to a bio based model v3 Christoph Hellwig
                   ` (14 preceding siblings ...)
  2021-05-12 13:15 ` [PATCH 15/15] nvme-multipath: enable polled I/O Christoph Hellwig
@ 2021-05-13 23:33 ` Wunderlich, Mark
  15 siblings, 0 replies; 40+ messages in thread
From: Wunderlich, Mark @ 2021-05-13 23:33 UTC (permalink / raw)
  To: Christoph Hellwig, Jens Axboe
  Cc: Jeffle Xu, Ming Lei, Damien Le Moal, Keith Busch, Sagi Grimberg,
	Vasudevan, Anil, linux-block, linux-fsdevel, linux-nvme

As a data point, tested V2 and this V3 patch series, applied to my test initiator
currently running 5.10 branch of linux-nvme.

All results via FIO using the following options:  --time_based --runtime=60 --thread
--rw=randread --refill_buffers --direct=1 --ioengine=io_uring --hipri --fixedbufs --bs=4k
--iodepth=32 --iodepth_batch_complete_min=1 --iodepth_batch_complete_max=32
--iodepth_batch=8 --group_reporting --gtod_reduce=0 --disable_lat=0 , 
with only the queue depth, batch size, and number of job threads varied as indicated.

Tests are directed towards one or more remote nvme optane devices.

All data reported as:
IOPS (k), Avg Lat (usec), stdev (usec), 99.99 clat (usec)

For reference, baseline performance on this branch, running without nvme multipathing enabled, while using 'hipri' polling option:
[1 thread, QD 1, Batch 1]
33.1, 29.21, 1.42, 54.52
[1 thread, QD 32, Batch 8]
268, 101.17, 14.87, 139
[16 thread, QD 32, Batch 8]
1965, 247.25, 28.28, 449

This branch with nvme multipathing enabled, V2 of the patch series applied:
[1 thread, QD 1, Batch 1]
33, 29.22, 1.56, 54.01
[1 thread, QD 32, Batch 8]
259, 104.38, 15.04, 141
[16 thread, QD32, Batch 8]
1905, 255.52, 30.97, 461

The same config as above for V2, but FIO results when not using 'hipri' polling option:
[1 thread, QD 1, Batch 1]
22.9k, 41.66, 3.78, 78.33
[1 thread, QD 32, Batch 8]
224k, 103.88, 28.41, 163
[16 thread, QD32, Batch 8]
1910k, 245.23, 66.30, 502

The same branch but with V3 of the patch series applied.  Again using the 'hipri' option:
[1 thread, QD 1, Batch 1]
33.2, 29.12, 1.35, 54.53
[1 thread, QD 32, Batch 8]
258, 104.55, 15.01, 141
[16 thread, QD32, Batch 8]
1914, 254.19, 30.00,  457

So the data shows that this patch series clearly enables the use of 'hipri' polling when
kernel configured with nvme multipathing, which was not previously supported.

There is not a significant difference in performance measured with and without
multipathing enabled, with either patch series for bio based polling.  And V2 and V3
reporting virtually the same performance as expected.

So I tip my hat to this patch series - cheers

Tested-by: Mark Wunderlich <mark.wunderlich@intel.com>


^ permalink raw reply	[flat|nested] 40+ messages in thread

* Re: [PATCH 12/15] block: switch polling to be bio based
  2021-05-12 22:12     ` Keith Busch
@ 2021-05-14  2:50       ` Keith Busch
  2021-05-14 16:26         ` Keith Busch
  0 siblings, 1 reply; 40+ messages in thread
From: Keith Busch @ 2021-05-14  2:50 UTC (permalink / raw)
  To: Sagi Grimberg
  Cc: Christoph Hellwig, Jens Axboe, Jeffle Xu, Ming Lei,
	Damien Le Moal, Wunderlich, Mark, Vasudevan, Anil, linux-block,
	linux-fsdevel, linux-nvme

On Wed, May 12, 2021 at 03:12:37PM -0700, Keith Busch wrote:
> On Wed, May 12, 2021 at 03:03:40PM -0700, Sagi Grimberg wrote:
> > On 5/12/21 6:15 AM, Christoph Hellwig wrote:
> > > + *
> > > + * Note: the caller must either be the context that submitted @bio, or
> > > + * be in a RCU critical section to prevent freeing of @bio.
> > > + */
> > > +int bio_poll(struct bio *bio, unsigned int flags)
> > > +{
> > > +	struct request_queue *q = bio->bi_bdev->bd_disk->queue;
> > > +	blk_qc_t cookie = READ_ONCE(bio->bi_cookie);
> > > +
> > > +	if (cookie == BLK_QC_T_NONE ||
> > > +	    !test_bit(QUEUE_FLAG_POLL, &q->queue_flags))
> > > +		return 0;
> > > +
> > > +	if (current->plug)
> > > +		blk_flush_plug_list(current->plug, false);
> > > +
> > > +	/* not yet implemented, so this should not happen */
> > > +	if (WARN_ON_ONCE(!queue_is_mq(q)))
> > 
> > What happens if the I/O wasn't (yet) queued to the bottom device
> > (i.e. no available path in nvme-mpath)?
> > 
> > In this case the disk would be the mpath device node (which is
> > not mq...)
> 
> The bi_cookie should remain BLK_QC_T_NONE in that case, so we wouldn't
> get to the warning. But if that does happen, it doesn't appear that
> anyone is going to wake up thread that needs to poll for this bio's
> completion when a path becomes available for dispatch. I think it would
> make sense for nvme-mpath to just clear the REQ_POLLED flag if it
> doesn't immediately have viable path.

It looks like there is a way to hit this warning. If you induce a path
error to create a failover, the nvme-mpath will reset the bio's bdev to
the mpath one, which is not MQ. I can occaisionally hit it with a fault
injection test.

^ permalink raw reply	[flat|nested] 40+ messages in thread

* Re: [PATCH 12/15] block: switch polling to be bio based
  2021-05-14  2:50       ` Keith Busch
@ 2021-05-14 16:26         ` Keith Busch
  2021-05-14 16:28           ` Christoph Hellwig
  0 siblings, 1 reply; 40+ messages in thread
From: Keith Busch @ 2021-05-14 16:26 UTC (permalink / raw)
  To: Sagi Grimberg
  Cc: Christoph Hellwig, Jens Axboe, Jeffle Xu, Ming Lei,
	Damien Le Moal, Wunderlich, Mark, Vasudevan, Anil, linux-block,
	linux-fsdevel, linux-nvme

On Thu, May 13, 2021 at 07:50:26PM -0700, Keith Busch wrote:
> On Wed, May 12, 2021 at 03:12:37PM -0700, Keith Busch wrote:
> > On Wed, May 12, 2021 at 03:03:40PM -0700, Sagi Grimberg wrote:
> > > On 5/12/21 6:15 AM, Christoph Hellwig wrote:
> > > > + *
> > > > + * Note: the caller must either be the context that submitted @bio, or
> > > > + * be in a RCU critical section to prevent freeing of @bio.
> > > > + */
> > > > +int bio_poll(struct bio *bio, unsigned int flags)
> > > > +{
> > > > +	struct request_queue *q = bio->bi_bdev->bd_disk->queue;
> > > > +	blk_qc_t cookie = READ_ONCE(bio->bi_cookie);
> > > > +
> > > > +	if (cookie == BLK_QC_T_NONE ||
> > > > +	    !test_bit(QUEUE_FLAG_POLL, &q->queue_flags))
> > > > +		return 0;
> > > > +
> > > > +	if (current->plug)
> > > > +		blk_flush_plug_list(current->plug, false);
> > > > +
> > > > +	/* not yet implemented, so this should not happen */
> > > > +	if (WARN_ON_ONCE(!queue_is_mq(q)))
> > > 
> > > What happens if the I/O wasn't (yet) queued to the bottom device
> > > (i.e. no available path in nvme-mpath)?
> > > 
> > > In this case the disk would be the mpath device node (which is
> > > not mq...)
> > 
> > The bi_cookie should remain BLK_QC_T_NONE in that case, so we wouldn't
> > get to the warning. But if that does happen, it doesn't appear that
> > anyone is going to wake up thread that needs to poll for this bio's
> > completion when a path becomes available for dispatch. I think it would
> > make sense for nvme-mpath to just clear the REQ_POLLED flag if it
> > doesn't immediately have viable path.
> 
> It looks like there is a way to hit this warning. If you induce a path
> error to create a failover, the nvme-mpath will reset the bio's bdev to
> the mpath one, which is not MQ. I can occaisionally hit it with a fault
> injection test.

Oh, and it gets a bit worse. Using pvsync2 will block forever once this
warning is hit, or if nvme-mpath had to requeue the IO for lack of a
path. io_uring doesn't have that hang problem though.

Christoph, I think patch 15 needs something like this:

---
diff --git a/drivers/nvme/host/multipath.c b/drivers/nvme/host/multipath.c
index 7febdb57f690..d40a9331daf7 100644
--- a/drivers/nvme/host/multipath.c
+++ b/drivers/nvme/host/multipath.c
@@ -419,6 +419,11 @@ static void nvme_requeue_work(struct work_struct *work)
 		 * path.
 		 */
 		bio_set_dev(bio, head->disk->part0);
+
+		if (bio->bi_opf & REQ_POLLED) {
+			bio->bi_opf &= ~REQ_POLLED;
+			bio->bi_cookie = BLK_QC_T_NONE;
+		}
 		submit_bio_noacct(bio);
 	}
 }
--

This should fix the hang since requeued bio's will use an interrupt
driven queue, but it doesn't fix the warning. The recent commit
"nvme-multipath: reset bdev to ns head when failover" looks like it
makes preventing the polling thread from using the non-MQ head disk
not possible.

^ permalink raw reply	[flat|nested] 40+ messages in thread

* Re: [PATCH 12/15] block: switch polling to be bio based
  2021-05-14 16:26         ` Keith Busch
@ 2021-05-14 16:28           ` Christoph Hellwig
  0 siblings, 0 replies; 40+ messages in thread
From: Christoph Hellwig @ 2021-05-14 16:28 UTC (permalink / raw)
  To: Keith Busch
  Cc: Sagi Grimberg, Christoph Hellwig, Jens Axboe, Jeffle Xu,
	Ming Lei, Damien Le Moal, Wunderlich, Mark, Vasudevan, Anil,
	linux-block, linux-fsdevel, linux-nvme

On Fri, May 14, 2021 at 09:26:12AM -0700, Keith Busch wrote:
> diff --git a/drivers/nvme/host/multipath.c b/drivers/nvme/host/multipath.c
> index 7febdb57f690..d40a9331daf7 100644
> --- a/drivers/nvme/host/multipath.c
> +++ b/drivers/nvme/host/multipath.c
> @@ -419,6 +419,11 @@ static void nvme_requeue_work(struct work_struct *work)
>  		 * path.
>  		 */
>  		bio_set_dev(bio, head->disk->part0);
> +
> +		if (bio->bi_opf & REQ_POLLED) {
> +			bio->bi_opf &= ~REQ_POLLED;
> +			bio->bi_cookie = BLK_QC_T_NONE;
> +		}
>  		submit_bio_noacct(bio);
>  	}
>  }
> --
> 
> This should fix the hang since requeued bio's will use an interrupt
> driven queue, but it doesn't fix the warning. The recent commit
> "nvme-multipath: reset bdev to ns head when failover" looks like it
> makes preventing the polling thread from using the non-MQ head disk
> not possible.

Yes.  Althought I'd rather move the code together with the bio stealing
in nvme_failover_req (and possibly move it into a block layer helper
as it is too subtle to be open coded in drivers).

^ permalink raw reply	[flat|nested] 40+ messages in thread

* Re: [PATCH 02/15] block: don't try to poll multi-bio I/Os in __blkdev_direct_IO
  2021-05-12 13:15 ` [PATCH 02/15] block: don't try to poll multi-bio I/Os in __blkdev_direct_IO Christoph Hellwig
  2021-05-12 20:54   ` Sagi Grimberg
@ 2021-05-16 18:01   ` Kanchan Joshi
  1 sibling, 0 replies; 40+ messages in thread
From: Kanchan Joshi @ 2021-05-16 18:01 UTC (permalink / raw)
  To: Christoph Hellwig
  Cc: Jens Axboe, Jeffle Xu, Ming Lei, Damien Le Moal, Keith Busch,
	Sagi Grimberg, Wunderlich, Mark, Vasudevan, Anil, linux-block,
	linux-fsdevel, linux-nvme

On Wed, May 12, 2021 at 6:50 PM Christoph Hellwig <hch@lst.de> wrote:
>
> If an iocb is split into multiple bios we can't poll for both.  So don't
> bother to even try to poll in that case.
>
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> ---
>  fs/block_dev.c | 37 ++++++++++++++-----------------------
>  1 file changed, 14 insertions(+), 23 deletions(-)
>
> diff --git a/fs/block_dev.c b/fs/block_dev.c
> index b8abccd03e5d..0080a3b710b4 100644
> --- a/fs/block_dev.c
> +++ b/fs/block_dev.c
> @@ -375,7 +375,7 @@ static ssize_t __blkdev_direct_IO(struct kiocb *iocb, struct iov_iter *iter,
>         struct blk_plug plug;
>         struct blkdev_dio *dio;
>         struct bio *bio;
> -       bool is_poll = (iocb->ki_flags & IOCB_HIPRI) != 0;
> +       bool is_poll = (iocb->ki_flags & IOCB_HIPRI), do_poll = false;
>         bool is_read = (iov_iter_rw(iter) == READ), is_sync;
>         loff_t pos = iocb->ki_pos;
>         blk_qc_t qc = BLK_QC_T_NONE;
> @@ -437,22 +437,9 @@ static ssize_t __blkdev_direct_IO(struct kiocb *iocb, struct iov_iter *iter,
>                 pos += bio->bi_iter.bi_size;
>
>                 nr_pages = bio_iov_vecs_to_alloc(iter, BIO_MAX_VECS);
> -               if (!nr_pages) {
> -                       bool polled = false;
> -
> -                       if (iocb->ki_flags & IOCB_HIPRI) {
> -                               bio_set_polled(bio, iocb);
> -                               polled = true;
> -                       }
> -
> -                       qc = submit_bio(bio);
> -
> -                       if (polled)
> -                               WRITE_ONCE(iocb->ki_cookie, qc);
> -                       break;
> -               }
> -
> -               if (!dio->multi_bio) {
> +               if (dio->multi_bio) {
> +                       atomic_inc(&dio->ref);
> +               } else if (nr_pages) {
>                         /*
>                          * AIO needs an extra reference to ensure the dio
>                          * structure which is embedded into the first bio
> @@ -462,11 +449,16 @@ static ssize_t __blkdev_direct_IO(struct kiocb *iocb, struct iov_iter *iter,
>                                 bio_get(bio);
>                         dio->multi_bio = true;
>                         atomic_set(&dio->ref, 2);
> -               } else {
> -                       atomic_inc(&dio->ref);
> +               } else if (is_poll) {
> +                       bio_set_polled(bio, iocb);
> +                       do_poll = true;
> +               }
> +               qc = submit_bio(bio);
> +               if (!nr_pages) {
> +                       if (do_poll)
> +                               WRITE_ONCE(iocb->ki_cookie, qc);
> +                       break;
>                 }
> -
> -               submit_bio(bio);
>                 bio = bio_alloc(GFP_KERNEL, nr_pages);
>         }

dio->ref update goes amiss here.
For multi-bio, if the original code sets it as N, this will set it as
N+1, causing endless-wait for the caller.

-- 
Kanchan

^ permalink raw reply	[flat|nested] 40+ messages in thread

* Re: [PATCH 08/15] io_uring: don't sleep when polling for I/O
  2021-05-12 21:55   ` Sagi Grimberg
@ 2021-05-19 13:02     ` Christoph Hellwig
  0 siblings, 0 replies; 40+ messages in thread
From: Christoph Hellwig @ 2021-05-19 13:02 UTC (permalink / raw)
  To: Sagi Grimberg
  Cc: Christoph Hellwig, Jens Axboe, Jeffle Xu, Ming Lei,
	Damien Le Moal, Keith Busch, Wunderlich, Mark, Vasudevan, Anil,
	linux-block, linux-fsdevel, linux-nvme

On Wed, May 12, 2021 at 02:55:59PM -0700, Sagi Grimberg wrote:
> I think that the combination of oneshot and nosleep flags to replace
> a boolen spin is a little hard to follow (especially that spin doesn't
> mean spinning without sleeping).
>
> Maybe we should break it to:
> 1. replace spin to flags with ONESHOT passed from io_uring (direct
>    replacement)
> 2. add NOSLEEP passed from io_uring as there is no need for it.
>
> Just a suggestion though that would help (me at least) to follow
> this more easily.

I've split it up for the next version.

^ permalink raw reply	[flat|nested] 40+ messages in thread

* [PATCH 09/15] block: rename REQ_HIPRI to REQ_POLLED
  2021-04-27 16:16 switch block layer polling to a bio based model v2 Christoph Hellwig
@ 2021-04-27 16:16 ` Christoph Hellwig
  0 siblings, 0 replies; 40+ messages in thread
From: Christoph Hellwig @ 2021-04-27 16:16 UTC (permalink / raw)
  To: Jens Axboe
  Cc: Jeffle Xu, Ming Lei, Damien Le Moal, Keith Busch, Sagi Grimberg,
	Wunderlich, Mark, Vasudevan, Anil, linux-block, linux-fsdevel

Unlike the RWF_HIPRI userspace ABI which is intentionally kept vague,
the bio flag is specіfic to the polling implementation, so rename and
document it properly.

Signed-off-by: Christoph Hellwig <hch@lst.de>
---
 block/blk-core.c          | 2 +-
 block/blk-merge.c         | 2 +-
 block/blk-mq-debugfs.c    | 2 +-
 block/blk-mq.c            | 4 ++--
 block/blk-mq.h            | 4 ++--
 drivers/nvme/host/core.c  | 2 +-
 include/linux/bio.h       | 2 +-
 include/linux/blk_types.h | 4 ++--
 mm/page_io.c              | 2 +-
 9 files changed, 12 insertions(+), 12 deletions(-)

diff --git a/block/blk-core.c b/block/blk-core.c
index 9bcdae93f6d4..adfab5976be0 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -837,7 +837,7 @@ static noinline_for_stack bool submit_bio_checks(struct bio *bio)
 	}
 
 	if (!test_bit(QUEUE_FLAG_POLL, &q->queue_flags))
-		bio->bi_opf &= ~REQ_HIPRI;
+		bio->bi_opf &= ~REQ_POLLED;
 
 	switch (bio_op(bio)) {
 	case REQ_OP_DISCARD:
diff --git a/block/blk-merge.c b/block/blk-merge.c
index 4d97fb6dd226..5c9d2a4ece86 100644
--- a/block/blk-merge.c
+++ b/block/blk-merge.c
@@ -285,7 +285,7 @@ static struct bio *blk_bio_segment_split(struct request_queue *q,
 	 * iopoll in direct IO routine. Given performance gain of iopoll for
 	 * big IO can be trival, disable iopoll when split needed.
 	 */
-	bio->bi_opf &= ~REQ_HIPRI;
+	bio->bi_opf &= ~REQ_POLLED;
 
 	return bio_split(bio, sectors, GFP_NOIO, bs);
 }
diff --git a/block/blk-mq-debugfs.c b/block/blk-mq-debugfs.c
index 2a75bc7401df..0b821b369ffd 100644
--- a/block/blk-mq-debugfs.c
+++ b/block/blk-mq-debugfs.c
@@ -286,7 +286,7 @@ static const char *const cmd_flag_name[] = {
 	CMD_FLAG_NAME(BACKGROUND),
 	CMD_FLAG_NAME(NOWAIT),
 	CMD_FLAG_NAME(NOUNMAP),
-	CMD_FLAG_NAME(HIPRI),
+	CMD_FLAG_NAME(POLLED),
 };
 #undef CMD_FLAG_NAME
 
diff --git a/block/blk-mq.c b/block/blk-mq.c
index 2e8a38618ebb..b35700710ef9 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -667,7 +667,7 @@ bool blk_mq_complete_request_remote(struct request *rq)
 	 * For a polled request, always complete locallly, it's pointless
 	 * to redirect the completion.
 	 */
-	if (rq->cmd_flags & REQ_HIPRI)
+	if (rq->cmd_flags & REQ_POLLED)
 		return false;
 
 	if (blk_mq_complete_need_ipi(rq)) {
@@ -2201,7 +2201,7 @@ blk_qc_t blk_mq_submit_bio(struct bio *bio)
 
 	rq_qos_throttle(q, bio);
 
-	hipri = bio->bi_opf & REQ_HIPRI;
+	hipri = bio->bi_opf & REQ_POLLED;
 
 	data.cmd_flags = bio->bi_opf;
 	rq = __blk_mq_alloc_request(&data);
diff --git a/block/blk-mq.h b/block/blk-mq.h
index 3616453ca28c..38eac0434a52 100644
--- a/block/blk-mq.h
+++ b/block/blk-mq.h
@@ -108,9 +108,9 @@ static inline struct blk_mq_hw_ctx *blk_mq_map_queue(struct request_queue *q,
 	enum hctx_type type = HCTX_TYPE_DEFAULT;
 
 	/*
-	 * The caller ensure that if REQ_HIPRI, poll must be enabled.
+	 * The caller ensure that if REQ_POLLED, poll must be enabled.
 	 */
-	if (flags & REQ_HIPRI)
+	if (flags & REQ_POLLED)
 		type = HCTX_TYPE_POLL;
 	else if ((flags & REQ_OP_MASK) == REQ_OP_READ)
 		type = HCTX_TYPE_READ;
diff --git a/drivers/nvme/host/core.c b/drivers/nvme/host/core.c
index f736fd36147c..0a8592f916cc 100644
--- a/drivers/nvme/host/core.c
+++ b/drivers/nvme/host/core.c
@@ -963,7 +963,7 @@ static void nvme_execute_rq_polled(struct request_queue *q,
 
 	WARN_ON_ONCE(!test_bit(QUEUE_FLAG_POLL, &q->queue_flags));
 
-	rq->cmd_flags |= REQ_HIPRI;
+	rq->cmd_flags |= REQ_POLLED;
 	rq->end_io_data = &wait;
 	blk_execute_rq_nowait(bd_disk, rq, at_head, nvme_end_sync_rq);
 
diff --git a/include/linux/bio.h b/include/linux/bio.h
index a0b4cfdf62a4..439a70bc42e2 100644
--- a/include/linux/bio.h
+++ b/include/linux/bio.h
@@ -817,7 +817,7 @@ static inline int bio_integrity_add_page(struct bio *bio, struct page *page,
  */
 static inline void bio_set_polled(struct bio *bio, struct kiocb *kiocb)
 {
-	bio->bi_opf |= REQ_HIPRI;
+	bio->bi_opf |= REQ_POLLED;
 	if (!is_sync_kiocb(kiocb))
 		bio->bi_opf |= REQ_NOWAIT;
 }
diff --git a/include/linux/blk_types.h b/include/linux/blk_types.h
index d0cf835d3b50..ac60432752e3 100644
--- a/include/linux/blk_types.h
+++ b/include/linux/blk_types.h
@@ -392,7 +392,7 @@ enum req_flag_bits {
 	/* command specific flags for REQ_OP_WRITE_ZEROES: */
 	__REQ_NOUNMAP,		/* do not free blocks when zeroing */
 
-	__REQ_HIPRI,
+	__REQ_POLLED,		/* caller polls for completion using blk_poll */
 
 	/* for driver use */
 	__REQ_DRV,
@@ -417,7 +417,7 @@ enum req_flag_bits {
 #define REQ_CGROUP_PUNT		(1ULL << __REQ_CGROUP_PUNT)
 
 #define REQ_NOUNMAP		(1ULL << __REQ_NOUNMAP)
-#define REQ_HIPRI		(1ULL << __REQ_HIPRI)
+#define REQ_POLLED		(1ULL << __REQ_POLLED)
 
 #define REQ_DRV			(1ULL << __REQ_DRV)
 #define REQ_SWAP		(1ULL << __REQ_SWAP)
diff --git a/mm/page_io.c b/mm/page_io.c
index 5d5543fcefa4..ed2eded74f3a 100644
--- a/mm/page_io.c
+++ b/mm/page_io.c
@@ -416,7 +416,7 @@ int swap_readpage(struct page *page, bool synchronous)
 	 * attempt to access it in the page fault retry time check.
 	 */
 	if (synchronous) {
-		bio->bi_opf |= REQ_HIPRI;
+		bio->bi_opf |= REQ_POLLED;
 		get_task_struct(current);
 		bio->bi_private = current;
 	}
-- 
2.30.1


^ permalink raw reply	[flat|nested] 40+ messages in thread

end of thread, other threads:[~2021-05-19 13:02 UTC | newest]

Thread overview: 40+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2021-05-12 13:15 switch block layer polling to a bio based model v3 Christoph Hellwig
2021-05-12 13:15 ` [PATCH 01/15] direct-io: remove blk_poll support Christoph Hellwig
2021-05-12 13:15 ` [PATCH 02/15] block: don't try to poll multi-bio I/Os in __blkdev_direct_IO Christoph Hellwig
2021-05-12 20:54   ` Sagi Grimberg
2021-05-16 18:01   ` Kanchan Joshi
2021-05-12 13:15 ` [PATCH 03/15] iomap: don't try to poll multi-bio I/Os in __iomap_dio_rw Christoph Hellwig
2021-05-12 21:32   ` Darrick J. Wong
2021-05-12 13:15 ` [PATCH 04/15] blk-mq: factor out a blk_qc_to_hctx helper Christoph Hellwig
2021-05-12 20:58   ` Sagi Grimberg
2021-05-12 13:15 ` [PATCH 05/15] blk-mq: factor out a "classic" poll helper Christoph Hellwig
2021-05-12 20:59   ` Sagi Grimberg
2021-05-12 13:15 ` [PATCH 06/15] blk-mq: remove blk_qc_t_to_tag and blk_qc_t_is_internal Christoph Hellwig
2021-05-12 21:42   ` Sagi Grimberg
2021-05-12 13:15 ` [PATCH 07/15] blk-mq: remove blk_qc_t_valid Christoph Hellwig
2021-05-12 21:43   ` Sagi Grimberg
2021-05-12 13:15 ` [PATCH 08/15] io_uring: don't sleep when polling for I/O Christoph Hellwig
2021-05-12 21:55   ` Sagi Grimberg
2021-05-19 13:02     ` Christoph Hellwig
2021-05-12 13:15 ` [PATCH 09/15] block: rename REQ_HIPRI to REQ_POLLED Christoph Hellwig
2021-05-12 21:56   ` Sagi Grimberg
2021-05-12 22:43   ` Chaitanya Kulkarni
2021-05-12 13:15 ` [PATCH 10/15] block: use SLAB_TYPESAFE_BY_RCU for the bio slab Christoph Hellwig
2021-05-12 13:15 ` [PATCH 11/15] block: define 'struct bvec_iter' as packed Christoph Hellwig
2021-05-12 21:58   ` Sagi Grimberg
2021-05-12 13:15 ` [PATCH 12/15] block: switch polling to be bio based Christoph Hellwig
2021-05-12 22:03   ` Sagi Grimberg
2021-05-12 22:12     ` Keith Busch
2021-05-14  2:50       ` Keith Busch
2021-05-14 16:26         ` Keith Busch
2021-05-14 16:28           ` Christoph Hellwig
2021-05-13  1:26     ` Ming Lei
2021-05-13  1:23   ` Ming Lei
2021-05-12 13:15 ` [PATCH 13/15] block: don't allow writing to the poll queue attribute Christoph Hellwig
2021-05-12 22:04   ` Sagi Grimberg
2021-05-12 13:15 ` [PATCH 14/15] nvme-multipath: set QUEUE_FLAG_NOWAIT Christoph Hellwig
2021-05-12 13:15 ` [PATCH 15/15] nvme-multipath: enable polled I/O Christoph Hellwig
2021-05-12 22:10   ` Sagi Grimberg
2021-05-12 22:16     ` Keith Busch
2021-05-13 23:33 ` switch block layer polling to a bio based model v3 Wunderlich, Mark
  -- strict thread matches above, loose matches on Subject: below --
2021-04-27 16:16 switch block layer polling to a bio based model v2 Christoph Hellwig
2021-04-27 16:16 ` [PATCH 09/15] block: rename REQ_HIPRI to REQ_POLLED Christoph Hellwig

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