nvme: wire up async polling for io passthrough commands

Store a cookie during submission, and use that to implement
completion-polling inside the ->uring_cmd_iopoll handler.
This handler makes use of existing bio poll facility.

Signed-off-by: Kanchan Joshi <[email protected]>
Signed-off-by: Anuj Gupta <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Jens Axboe <[email protected]>

Author: Kanchan Joshi

drivers/nvme/host/core.c

@@ -3976,6 +3976,7 @@ static const struct file_operations nvme_ns_chr_fops = {
 	.unlocked_ioctl	= nvme_ns_chr_ioctl,
 	.compat_ioctl	= compat_ptr_ioctl,
 	.uring_cmd	= nvme_ns_chr_uring_cmd,
+	.uring_cmd_iopoll = nvme_ns_chr_uring_cmd_iopoll,
 };
 
 static int nvme_add_ns_cdev(struct nvme_ns *ns)

drivers/nvme/host/ioctl.c

@@ -391,11 +391,19 @@ static void nvme_uring_cmd_end_io(struct request *req, blk_status_t err)
 	struct nvme_uring_cmd_pdu *pdu = nvme_uring_cmd_pdu(ioucmd);
 	/* extract bio before reusing the same field for request */
 	struct bio *bio = pdu->bio;
+	void *cookie = READ_ONCE(ioucmd->cookie);
 
 	pdu->req = req;
 	req->bio = bio;
-	/* this takes care of moving rest of completion-work to task context */
-	io_uring_cmd_complete_in_task(ioucmd, nvme_uring_task_cb);
+
+	/*
+	 * For iopoll, complete it directly.
+	 * Otherwise, move the completion to task work.
+	 */
+	if (cookie != NULL && blk_rq_is_poll(req))
+		nvme_uring_task_cb(ioucmd);
+	else
+		io_uring_cmd_complete_in_task(ioucmd, nvme_uring_task_cb);
 }
 
 static int nvme_uring_cmd_io(struct nvme_ctrl *ctrl, struct nvme_ns *ns,
@@ -445,7 +453,10 @@ static int nvme_uring_cmd_io(struct nvme_ctrl *ctrl, struct nvme_ns *ns,
 		rq_flags = REQ_NOWAIT;
 		blk_flags = BLK_MQ_REQ_NOWAIT;
 	}
+	if (issue_flags & IO_URING_F_IOPOLL)
+		rq_flags |= REQ_POLLED;
 
+retry:
 	req = nvme_alloc_user_request(q, &c, nvme_to_user_ptr(d.addr),
 			d.data_len, nvme_to_user_ptr(d.metadata),
 			d.metadata_len, 0, &meta, d.timeout_ms ?
@@ -456,6 +467,17 @@ static int nvme_uring_cmd_io(struct nvme_ctrl *ctrl, struct nvme_ns *ns,
 	req->end_io = nvme_uring_cmd_end_io;
 	req->end_io_data = ioucmd;
 
+	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;
+		}
+	}
 	/* to free bio on completion, as req->bio will be null at that time */
 	pdu->bio = req->bio;
 	pdu->meta = meta;
@@ -559,9 +581,6 @@ long nvme_ns_chr_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
 
 static int nvme_uring_cmd_checks(unsigned int issue_flags)
 {
-	/* IOPOLL not supported yet */
-	if (issue_flags & IO_URING_F_IOPOLL)
-		return -EOPNOTSUPP;
 
 	/* NVMe passthrough requires big SQE/CQE support */
 	if ((issue_flags & (IO_URING_F_SQE128|IO_URING_F_CQE32)) !=
@@ -604,6 +623,23 @@ int nvme_ns_chr_uring_cmd(struct io_uring_cmd *ioucmd, unsigned int issue_flags)
 	return nvme_ns_uring_cmd(ns, ioucmd, issue_flags);
 }
 
+int nvme_ns_chr_uring_cmd_iopoll(struct io_uring_cmd *ioucmd)
+{
+	struct bio *bio;
+	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, NULL, 0);
+	rcu_read_unlock();
+	return ret;
+}
 #ifdef CONFIG_NVME_MULTIPATH
 static int nvme_ns_head_ctrl_ioctl(struct nvme_ns *ns, unsigned int cmd,
 		void __user *argp, struct nvme_ns_head *head, int srcu_idx)
@@ -685,13 +721,40 @@ 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 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, NULL, 0);
+		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)
 {
 	struct nvme_ctrl *ctrl = ioucmd->file->private_data;
 	int ret;
 
+	/* IOPOLL not supported yet */
+	if (issue_flags & IO_URING_F_IOPOLL)
+		return -EOPNOTSUPP;
+
 	ret = nvme_uring_cmd_checks(issue_flags);
 	if (ret)
 		return ret;

drivers/nvme/host/multipath.c

@@ -439,6 +439,7 @@ 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,
 };
 
 static int nvme_add_ns_head_cdev(struct nvme_ns_head *head)

drivers/nvme/host/nvme.h

@@ -821,6 +821,8 @@ long nvme_ns_head_chr_ioctl(struct file *file, unsigned int cmd,
 		unsigned long arg);
 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);
+int nvme_ns_head_chr_uring_cmd_iopoll(struct io_uring_cmd *ioucmd);
 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,