[PATCH v9 05/29] libmultipath: Add bio handling

[John Garry <john.garry@linux.dev>]

Add support to submit a bio per-path. In addition, for failover, add
support to requeue a failed bio.

NVMe has almost like-for-like equivalents here:
    - nvme_available_path() -> mpath_available_path()
    - nvme_requeue_work() -> mpath_requeue_work()
    - nvme_ns_head_submit_bio() -> mpath_bdev_submit_bio()

For failover, a driver may want to re-submit a bio, so add support to
clone a bio prior to submission.

A bio which is submitted to a per-path device has flag REQ_MPATH set,
same as what is done for NVMe with REQ_NVME_MPATH.

Signed-off-by: John Garry <john.garry@linux.dev>
---
 include/linux/multipath.h |  22 ++++++++
 lib/multipath.c           | 108 +++++++++++++++++++++++++++++++++++++-
 2 files changed, 128 insertions(+), 2 deletions(-)

diff --git a/include/linux/multipath.h b/include/linux/multipath.h
index 9bbab0aa8961..374f0531f7e0 100644
--- a/include/linux/multipath.h
+++ b/include/linux/multipath.h
@@ -3,6 +3,7 @@
 #define _LIBMULTIPATH_H
 
 #include <linux/blkdev.h>
+#include <linux/blk-mq.h>
 #include <linux/srcu.h>
 
 extern const struct block_device_operations mpath_ops;
@@ -29,8 +30,10 @@ struct mpath_device {
 };
 
 struct mpath_head_template {
+	bool (*available_path)(struct mpath_device *);
 	bool (*is_disabled)(struct mpath_device *);
 	bool (*is_optimized)(struct mpath_device *);
+	struct bio *(*clone_bio)(struct bio *);
 	const struct attribute_group **device_groups;
 };
 
@@ -44,6 +47,14 @@ struct mpath_head {
 	refcount_t		refcount;
 
 	enum mpath_iopolicy_e	*iopolicy;
+
+	struct bio_list		requeue_list; /* list for requeing bio */
+	spinlock_t		requeue_lock;
+	struct work_struct	requeue_work; /* work struct for requeue */
+
+	atomic_long_t		requeue_no_usable_path_cnt;
+	atomic_long_t		fail_no_avail_path_cnt;
+
 	unsigned long		flags;
 	struct gendisk		*disk;
 	struct work_struct	partition_scan_work;
@@ -53,6 +64,13 @@ struct mpath_head {
 	struct mpath_device __rcu 		*current_path[MAX_NUMNODES];
 };
 
+#define REQ_MPATH		REQ_DRV
+
+static inline bool is_mpath_request(struct request *req)
+{
+	return req->cmd_flags & REQ_MPATH;
+}
+
 static inline struct mpath_head *mpath_bd_device_to_head(struct device *dev)
 {
 	return dev_get_drvdata(dev);
@@ -96,4 +114,8 @@ static inline bool mpath_qd_iopolicy(enum mpath_iopolicy_e *iopolicy)
 	return READ_ONCE(*iopolicy) == MPATH_IOPOLICY_QD;
 }
 
+static inline void mpath_schedule_requeue_work(struct mpath_head *mpath_head)
+{
+	kblockd_schedule_work(&mpath_head->requeue_work);
+}
 #endif // _LIBMULTIPATH_H
diff --git a/lib/multipath.c b/lib/multipath.c
index b8ea8478037e..5dc7994f8095 100644
--- a/lib/multipath.c
+++ b/lib/multipath.c
@@ -7,6 +7,7 @@
 #include <linux/module.h>
 #include <linux/multipath.h>
 #include <linux/wait_bit.h>
+#include <trace/events/block.h>
 
 static struct mpath_device *mpath_find_path(struct mpath_head *mpath_head);
 
@@ -45,7 +46,6 @@ int mpath_get_iopolicy(char *buf, int iopolicy)
 }
 EXPORT_SYMBOL_GPL(mpath_get_iopolicy);
 
-
 void mpath_synchronize(struct mpath_head *mpath_head)
 {
 	synchronize_srcu(&mpath_head->srcu);
@@ -232,7 +232,6 @@ static struct mpath_device *mpath_numa_path(struct mpath_head *mpath_head)
 	return mpath_device;
 }
 
-__maybe_unused
 static struct mpath_device *mpath_find_path(struct mpath_head *mpath_head)
 {
 	enum mpath_iopolicy_e iopolicy = mpath_read_iopolicy(mpath_head);
@@ -247,6 +246,81 @@ static struct mpath_device *mpath_find_path(struct mpath_head *mpath_head)
 	}
 }
 
+static bool mpath_available_path(struct mpath_head *mpath_head)
+{
+	struct mpath_device *mpath_device;
+
+	if (!test_bit(MPATH_HEAD_DISK_LIVE, &mpath_head->flags))
+		return false;
+
+	list_for_each_entry_srcu(mpath_device, &mpath_head->dev_list, siblings,
+				 srcu_read_lock_held(&mpath_head->srcu)) {
+		if (mpath_head->mpdt->available_path(mpath_device))
+			return true;
+	}
+
+	return false;
+}
+
+static void mpath_bdev_submit_bio(struct bio *bio)
+{
+	struct mpath_head *mpath_head = bio->bi_bdev->bd_disk->private_data;
+	struct device *dev = mpath_head->parent;
+	struct mpath_device *mpath_device;
+	int srcu_idx;
+
+	/*
+	 * The mpath_device might be going away and the bio might be moved to a
+	 * different queue in failover, so we need to use the bio_split
+	 * pool from the original queue to allocate the bvecs from.
+	 */
+	bio = bio_split_to_limits(bio);
+	if (!bio)
+		return;
+
+	srcu_idx = srcu_read_lock(&mpath_head->srcu);
+	mpath_device = mpath_find_path(mpath_head);
+
+	if (likely(mpath_device)) {
+		if (mpath_head->mpdt->clone_bio) {
+			struct bio *orig = bio;
+
+			bio = mpath_head->mpdt->clone_bio(bio);
+			if (!bio) {
+				bio_io_error(orig);
+				goto out;
+			}
+		}
+
+		bio_set_dev(bio, mpath_device->disk->part0);
+		/*
+		 * Use BIO_REMAPPED to skip bio_check_eod() when this bio
+		 * enters submit_bio_noacct() for the per-path device. The EOD
+		 * check already passed on the multipath head.
+		 */
+		bio_set_flag(bio, BIO_REMAPPED);
+		bio->bi_opf |= REQ_MPATH;
+		trace_block_bio_remap(bio, disk_devt(mpath_head->disk),
+				      bio->bi_iter.bi_sector);
+		submit_bio_noacct(bio);
+	} else if (mpath_available_path(mpath_head)) {
+		dev_warn_ratelimited(dev, "no usable path - requeuing I/O\n");
+
+		spin_lock_irq(&mpath_head->requeue_lock);
+		bio_list_add(&mpath_head->requeue_list, bio);
+		spin_unlock_irq(&mpath_head->requeue_lock);
+		atomic_long_inc(&mpath_head->requeue_no_usable_path_cnt);
+	} else {
+		dev_warn_ratelimited(dev, "no available path - failing I/O\n");
+
+		bio_io_error(bio);
+		atomic_long_inc(&mpath_head->fail_no_avail_path_cnt);
+	}
+
+out:
+	srcu_read_unlock(&mpath_head->srcu, srcu_idx);
+}
+
 int mpath_get_head(struct mpath_head *mpath_head)
 {
 	if (!refcount_inc_not_zero(&mpath_head->refcount))
@@ -292,6 +366,7 @@ const struct block_device_operations mpath_ops = {
 	.owner          = THIS_MODULE,
 	.open		= mpath_bdev_open,
 	.release	= mpath_bdev_release,
+	.submit_bio	= mpath_bdev_submit_bio,
 };
 EXPORT_SYMBOL_GPL(mpath_ops);
 
@@ -309,12 +384,35 @@ static void multipath_partition_scan_work(struct work_struct *work)
 	mutex_unlock(&mpath_head->disk->open_mutex);
 }
 
+static void mpath_requeue_work(struct work_struct *work)
+{
+	struct mpath_head *mpath_head =
+	    container_of(work, struct mpath_head, requeue_work);
+	struct bio *bio, *next;
+
+	spin_lock_irq(&mpath_head->requeue_lock);
+	next = bio_list_get(&mpath_head->requeue_list);
+	spin_unlock_irq(&mpath_head->requeue_lock);
+
+	while ((bio = next) != NULL) {
+		next = bio->bi_next;
+		bio->bi_next = NULL;
+		submit_bio_noacct(bio);
+	}
+}
+
 void mpath_remove_disk(struct mpath_head *mpath_head)
 {
 	if (test_and_clear_bit(MPATH_HEAD_DISK_LIVE, &mpath_head->flags)) {
 		struct gendisk *disk = mpath_head->disk;
 
+		/*
+		 * requeue I/O after MPATH_HEAD_DISK_LIVE has been cleared
+		 * to allow multipath to fail all I/O.
+		 */
 		mpath_synchronize(mpath_head);
+		mpath_schedule_requeue_work(mpath_head);
+
 		del_gendisk(disk);
 	}
 }
@@ -326,6 +424,8 @@ void mpath_put_disk(struct mpath_head *mpath_head)
 		return;
 
 	/* make sure all pending bios are cleaned up */
+	kblockd_schedule_work(&mpath_head->requeue_work);
+	flush_work(&mpath_head->requeue_work);
 	flush_work(&mpath_head->partition_scan_work);
 	put_disk(mpath_head->disk);
 	mpath_head->disk = NULL;
@@ -385,6 +485,7 @@ void mpath_device_set_live(struct mpath_device *mpath_device)
 	mutex_unlock(&mpath_head->lock);
 
 	mpath_synchronize(mpath_head);
+	mpath_schedule_requeue_work(mpath_head);
 }
 EXPORT_SYMBOL_GPL(mpath_device_set_live);
 
@@ -397,6 +498,9 @@ int mpath_head_init(struct mpath_head *mpath_head)
 
 	INIT_WORK(&mpath_head->partition_scan_work,
 		multipath_partition_scan_work);
+	INIT_WORK(&mpath_head->requeue_work, mpath_requeue_work);
+	spin_lock_init(&mpath_head->requeue_lock);
+	bio_list_init(&mpath_head->requeue_list);
 
 	return init_srcu_struct(&mpath_head->srcu);
 }
-- 
2.43.0