[PATCHv2 4/5] nvme: use blk-mq polling for uring commands

[Keith Busch <kbusch@meta.com>]

From: Keith Busch <kbusch@kernel.org>

Drivers can now poll requests directly, and the nvme uring command
unconditionally saves the request now, so use that. We just need to
clear it on completion to prevent any races among multiple threads
polling the same queues during a tagset teardown.

The first advantage is that unshared and multipath namespaces can use
the same polling callback, and multipath is guaranteed to get the same
queue as the command was submitted on. Previously multipath polling might
check a different path and poll the wrong info.

The other advantage is that we don't need a bio payload in order to
poll, allowing commands like 'flush' and 'write zeroes' to be submitted
on the same high priority queue as read and write commands.

This can also allow for a future optimization for the driver since we no
longer need to create special hidden block devices to back nvme-generic
char dev's with unsupported command sets.

Signed-off-by: Keith Busch <kbusch@kernel.org>
---
 drivers/nvme/host/ioctl.c     | 58 +++++------------------------------
 drivers/nvme/host/multipath.c |  2 +-
 drivers/nvme/host/nvme.h      |  2 --
 3 files changed, 9 insertions(+), 53 deletions(-)

diff --git a/drivers/nvme/host/ioctl.c b/drivers/nvme/host/ioctl.c
index a1e0a14dadedc..3604166752e4b 100644
--- a/drivers/nvme/host/ioctl.c
+++ b/drivers/nvme/host/ioctl.c
@@ -478,9 +478,9 @@ static enum rq_end_io_ret nvme_uring_cmd_end_io(struct request *req,
 {
 	struct io_uring_cmd *ioucmd = req->end_io_data;
 	struct nvme_uring_cmd_pdu *pdu = nvme_uring_cmd_pdu(ioucmd);
-	void *cookie = READ_ONCE(ioucmd->cookie);
 	int status = nvme_req(req)->status;
 
+	WRITE_ONCE(pdu->req, NULL);
 	if (nvme_req(req)->flags & NVME_REQ_CANCELLED)
 		status = -EINTR;
 
@@ -495,7 +495,7 @@ static enum rq_end_io_ret nvme_uring_cmd_end_io(struct request *req,
 	 * For iopoll, complete it directly.
 	 * Otherwise, move the completion to task work.
 	 */
-	if (cookie != NULL && blk_rq_is_poll(req))
+	if (blk_rq_is_poll(req))
 		nvme_uring_task_cb(ioucmd, IO_URING_F_UNLOCKED);
 	else
 		io_uring_cmd_complete_in_task(ioucmd, nvme_uring_task_cb);
@@ -554,7 +554,6 @@ static int nvme_uring_cmd_io(struct nvme_ctrl *ctrl, struct nvme_ns *ns,
 	if (issue_flags & IO_URING_F_IOPOLL)
 		rq_flags |= REQ_POLLED;
 
-retry:
 	req = nvme_alloc_user_request(q, &c, rq_flags, blk_flags);
 	if (IS_ERR(req))
 		return PTR_ERR(req);
@@ -568,19 +567,7 @@ static int nvme_uring_cmd_io(struct nvme_ctrl *ctrl, struct nvme_ns *ns,
 			return ret;
 	}
 
-	if (issue_flags & IO_URING_F_IOPOLL && rq_flags & REQ_POLLED) {
-		if (unlikely(!req->bio)) {
-			/* we can't poll this, so alloc regular req instead */
-			blk_mq_free_request(req);
-			rq_flags &= ~REQ_POLLED;
-			goto retry;
-		} else {
-			WRITE_ONCE(ioucmd->cookie, req->bio);
-			req->bio->bi_opf |= REQ_POLLED;
-		}
-	}
-
-	pdu->req = req;
+	WRITE_ONCE(pdu->req, req);
 	pdu->meta_len = d.metadata_len;
 	req->end_io_data = ioucmd;
 	req->end_io = nvme_uring_cmd_end_io;
@@ -735,18 +722,14 @@ int nvme_ns_chr_uring_cmd_iopoll(struct io_uring_cmd *ioucmd,
 				 struct io_comp_batch *iob,
 				 unsigned int poll_flags)
 {
-	struct bio *bio;
+	struct nvme_uring_cmd_pdu *pdu = nvme_uring_cmd_pdu(ioucmd);
+	struct request *req;
 	int ret = 0;
-	struct nvme_ns *ns;
-	struct request_queue *q;
 
 	rcu_read_lock();
-	bio = READ_ONCE(ioucmd->cookie);
-	ns = container_of(file_inode(ioucmd->file)->i_cdev,
-			struct nvme_ns, cdev);
-	q = ns->queue;
-	if (test_bit(QUEUE_FLAG_POLL, &q->queue_flags) && bio && bio->bi_bdev)
-		ret = bio_poll(bio, iob, poll_flags);
+	req = READ_ONCE(pdu->req);
+	if (req && blk_rq_is_poll(req))
+		ret = blk_rq_poll(req, iob, poll_flags);
 	rcu_read_unlock();
 	return ret;
 }
@@ -838,31 +821,6 @@ int nvme_ns_head_chr_uring_cmd(struct io_uring_cmd *ioucmd,
 	srcu_read_unlock(&head->srcu, srcu_idx);
 	return ret;
 }
-
-int nvme_ns_head_chr_uring_cmd_iopoll(struct io_uring_cmd *ioucmd,
-				      struct io_comp_batch *iob,
-				      unsigned int poll_flags)
-{
-	struct cdev *cdev = file_inode(ioucmd->file)->i_cdev;
-	struct nvme_ns_head *head = container_of(cdev, struct nvme_ns_head, cdev);
-	int srcu_idx = srcu_read_lock(&head->srcu);
-	struct nvme_ns *ns = nvme_find_path(head);
-	struct bio *bio;
-	int ret = 0;
-	struct request_queue *q;
-
-	if (ns) {
-		rcu_read_lock();
-		bio = READ_ONCE(ioucmd->cookie);
-		q = ns->queue;
-		if (test_bit(QUEUE_FLAG_POLL, &q->queue_flags) && bio
-				&& bio->bi_bdev)
-			ret = bio_poll(bio, iob, poll_flags);
-		rcu_read_unlock();
-	}
-	srcu_read_unlock(&head->srcu, srcu_idx);
-	return ret;
-}
 #endif /* CONFIG_NVME_MULTIPATH */
 
 int nvme_dev_uring_cmd(struct io_uring_cmd *ioucmd, unsigned int issue_flags)
diff --git a/drivers/nvme/host/multipath.c b/drivers/nvme/host/multipath.c
index 9171452e2f6d4..f17be1c72f4de 100644
--- a/drivers/nvme/host/multipath.c
+++ b/drivers/nvme/host/multipath.c
@@ -470,7 +470,7 @@ static const struct file_operations nvme_ns_head_chr_fops = {
 	.unlocked_ioctl	= nvme_ns_head_chr_ioctl,
 	.compat_ioctl	= compat_ptr_ioctl,
 	.uring_cmd	= nvme_ns_head_chr_uring_cmd,
-	.uring_cmd_iopoll = nvme_ns_head_chr_uring_cmd_iopoll,
+	.uring_cmd_iopoll = nvme_ns_chr_uring_cmd_iopoll,
 };
 
 static int nvme_add_ns_head_cdev(struct nvme_ns_head *head)
diff --git a/drivers/nvme/host/nvme.h b/drivers/nvme/host/nvme.h
index bf46f122e9e1e..ca4ea89333660 100644
--- a/drivers/nvme/host/nvme.h
+++ b/drivers/nvme/host/nvme.h
@@ -847,8 +847,6 @@ long nvme_dev_ioctl(struct file *file, unsigned int cmd,
 		unsigned long arg);
 int nvme_ns_chr_uring_cmd_iopoll(struct io_uring_cmd *ioucmd,
 		struct io_comp_batch *iob, unsigned int poll_flags);
-int nvme_ns_head_chr_uring_cmd_iopoll(struct io_uring_cmd *ioucmd,
-		struct io_comp_batch *iob, unsigned int poll_flags);
 int nvme_ns_chr_uring_cmd(struct io_uring_cmd *ioucmd,
 		unsigned int issue_flags);
 int nvme_ns_head_chr_uring_cmd(struct io_uring_cmd *ioucmd,
-- 
2.34.1