Adding upstream version 6.6.15.upstream/6.6.15

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 2270 insertions, 0 deletions

diff --git a/drivers/md/dm-mpath.c b/drivers/md/dm-mpath.c
new file mode 100644
index 0000000000..bea3cda993
--- /dev/null
+++ b/drivers/md/dm-mpath.c
@@ -0,0 +1,2270 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright (C) 2003 Sistina Software Limited.
+ * Copyright (C) 2004-2005 Red Hat, Inc. All rights reserved.
+ *
+ * This file is released under the GPL.
+ */
+
+#include <linux/device-mapper.h>
+
+#include "dm-rq.h"
+#include "dm-bio-record.h"
+#include "dm-path-selector.h"
+#include "dm-uevent.h"
+
+#include <linux/blkdev.h>
+#include <linux/ctype.h>
+#include <linux/init.h>
+#include <linux/mempool.h>
+#include <linux/module.h>
+#include <linux/pagemap.h>
+#include <linux/slab.h>
+#include <linux/time.h>
+#include <linux/timer.h>
+#include <linux/workqueue.h>
+#include <linux/delay.h>
+#include <scsi/scsi_dh.h>
+#include <linux/atomic.h>
+#include <linux/blk-mq.h>
+
+static struct workqueue_struct *dm_mpath_wq;
+
+#define DM_MSG_PREFIX "multipath"
+#define DM_PG_INIT_DELAY_MSECS 2000
+#define DM_PG_INIT_DELAY_DEFAULT ((unsigned int) -1)
+#define QUEUE_IF_NO_PATH_TIMEOUT_DEFAULT 0
+
+static unsigned long queue_if_no_path_timeout_secs = QUEUE_IF_NO_PATH_TIMEOUT_DEFAULT;
+
+/* Path properties */
+struct pgpath {
+	struct list_head list;
+
+	struct priority_group *pg;	/* Owning PG */
+	unsigned int fail_count;		/* Cumulative failure count */
+
+	struct dm_path path;
+	struct delayed_work activate_path;
+
+	bool is_active:1;		/* Path status */
+};
+
+#define path_to_pgpath(__pgp) container_of((__pgp), struct pgpath, path)
+
+/*
+ * Paths are grouped into Priority Groups and numbered from 1 upwards.
+ * Each has a path selector which controls which path gets used.
+ */
+struct priority_group {
+	struct list_head list;
+
+	struct multipath *m;		/* Owning multipath instance */
+	struct path_selector ps;
+
+	unsigned int pg_num;		/* Reference number */
+	unsigned int nr_pgpaths;		/* Number of paths in PG */
+	struct list_head pgpaths;
+
+	bool bypassed:1;		/* Temporarily bypass this PG? */
+};
+
+/* Multipath context */
+struct multipath {
+	unsigned long flags;		/* Multipath state flags */
+
+	spinlock_t lock;
+	enum dm_queue_mode queue_mode;
+
+	struct pgpath *current_pgpath;
+	struct priority_group *current_pg;
+	struct priority_group *next_pg;	/* Switch to this PG if set */
+
+	atomic_t nr_valid_paths;	/* Total number of usable paths */
+	unsigned int nr_priority_groups;
+	struct list_head priority_groups;
+
+	const char *hw_handler_name;
+	char *hw_handler_params;
+	wait_queue_head_t pg_init_wait;	/* Wait for pg_init completion */
+	unsigned int pg_init_retries;	/* Number of times to retry pg_init */
+	unsigned int pg_init_delay_msecs;	/* Number of msecs before pg_init retry */
+	atomic_t pg_init_in_progress;	/* Only one pg_init allowed at once */
+	atomic_t pg_init_count;		/* Number of times pg_init called */
+
+	struct mutex work_mutex;
+	struct work_struct trigger_event;
+	struct dm_target *ti;
+
+	struct work_struct process_queued_bios;
+	struct bio_list queued_bios;
+
+	struct timer_list nopath_timer;	/* Timeout for queue_if_no_path */
+};
+
+/*
+ * Context information attached to each io we process.
+ */
+struct dm_mpath_io {
+	struct pgpath *pgpath;
+	size_t nr_bytes;
+	u64 start_time_ns;
+};
+
+typedef int (*action_fn) (struct pgpath *pgpath);
+
+static struct workqueue_struct *kmultipathd, *kmpath_handlerd;
+static void trigger_event(struct work_struct *work);
+static void activate_or_offline_path(struct pgpath *pgpath);
+static void activate_path_work(struct work_struct *work);
+static void process_queued_bios(struct work_struct *work);
+static void queue_if_no_path_timeout_work(struct timer_list *t);
+
+/*
+ *-----------------------------------------------
+ * Multipath state flags.
+ *-----------------------------------------------
+ */
+#define MPATHF_QUEUE_IO 0			/* Must we queue all I/O? */
+#define MPATHF_QUEUE_IF_NO_PATH 1		/* Queue I/O if last path fails? */
+#define MPATHF_SAVED_QUEUE_IF_NO_PATH 2		/* Saved state during suspension */
+#define MPATHF_RETAIN_ATTACHED_HW_HANDLER 3	/* If there's already a hw_handler present, don't change it. */
+#define MPATHF_PG_INIT_DISABLED 4		/* pg_init is not currently allowed */
+#define MPATHF_PG_INIT_REQUIRED 5		/* pg_init needs calling? */
+#define MPATHF_PG_INIT_DELAY_RETRY 6		/* Delay pg_init retry? */
+
+static bool mpath_double_check_test_bit(int MPATHF_bit, struct multipath *m)
+{
+	bool r = test_bit(MPATHF_bit, &m->flags);
+
+	if (r) {
+		unsigned long flags;
+
+		spin_lock_irqsave(&m->lock, flags);
+		r = test_bit(MPATHF_bit, &m->flags);
+		spin_unlock_irqrestore(&m->lock, flags);
+	}
+
+	return r;
+}
+
+/*
+ *-----------------------------------------------
+ * Allocation routines
+ *-----------------------------------------------
+ */
+static struct pgpath *alloc_pgpath(void)
+{
+	struct pgpath *pgpath = kzalloc(sizeof(*pgpath), GFP_KERNEL);
+
+	if (!pgpath)
+		return NULL;
+
+	pgpath->is_active = true;
+
+	return pgpath;
+}
+
+static void free_pgpath(struct pgpath *pgpath)
+{
+	kfree(pgpath);
+}
+
+static struct priority_group *alloc_priority_group(void)
+{
+	struct priority_group *pg;
+
+	pg = kzalloc(sizeof(*pg), GFP_KERNEL);
+
+	if (pg)
+		INIT_LIST_HEAD(&pg->pgpaths);
+
+	return pg;
+}
+
+static void free_pgpaths(struct list_head *pgpaths, struct dm_target *ti)
+{
+	struct pgpath *pgpath, *tmp;
+
+	list_for_each_entry_safe(pgpath, tmp, pgpaths, list) {
+		list_del(&pgpath->list);
+		dm_put_device(ti, pgpath->path.dev);
+		free_pgpath(pgpath);
+	}
+}
+
+static void free_priority_group(struct priority_group *pg,
+				struct dm_target *ti)
+{
+	struct path_selector *ps = &pg->ps;
+
+	if (ps->type) {
+		ps->type->destroy(ps);
+		dm_put_path_selector(ps->type);
+	}
+
+	free_pgpaths(&pg->pgpaths, ti);
+	kfree(pg);
+}
+
+static struct multipath *alloc_multipath(struct dm_target *ti)
+{
+	struct multipath *m;
+
+	m = kzalloc(sizeof(*m), GFP_KERNEL);
+	if (m) {
+		INIT_LIST_HEAD(&m->priority_groups);
+		spin_lock_init(&m->lock);
+		atomic_set(&m->nr_valid_paths, 0);
+		INIT_WORK(&m->trigger_event, trigger_event);
+		mutex_init(&m->work_mutex);
+
+		m->queue_mode = DM_TYPE_NONE;
+
+		m->ti = ti;
+		ti->private = m;
+
+		timer_setup(&m->nopath_timer, queue_if_no_path_timeout_work, 0);
+	}
+
+	return m;
+}
+
+static int alloc_multipath_stage2(struct dm_target *ti, struct multipath *m)
+{
+	if (m->queue_mode == DM_TYPE_NONE) {
+		m->queue_mode = DM_TYPE_REQUEST_BASED;
+	} else if (m->queue_mode == DM_TYPE_BIO_BASED) {
+		INIT_WORK(&m->process_queued_bios, process_queued_bios);
+		/*
+		 * bio-based doesn't support any direct scsi_dh management;
+		 * it just discovers if a scsi_dh is attached.
+		 */
+		set_bit(MPATHF_RETAIN_ATTACHED_HW_HANDLER, &m->flags);
+	}
+
+	dm_table_set_type(ti->table, m->queue_mode);
+
+	/*
+	 * Init fields that are only used when a scsi_dh is attached
+	 * - must do this unconditionally (really doesn't hurt non-SCSI uses)
+	 */
+	set_bit(MPATHF_QUEUE_IO, &m->flags);
+	atomic_set(&m->pg_init_in_progress, 0);
+	atomic_set(&m->pg_init_count, 0);
+	m->pg_init_delay_msecs = DM_PG_INIT_DELAY_DEFAULT;
+	init_waitqueue_head(&m->pg_init_wait);
+
+	return 0;
+}
+
+static void free_multipath(struct multipath *m)
+{
+	struct priority_group *pg, *tmp;
+
+	list_for_each_entry_safe(pg, tmp, &m->priority_groups, list) {
+		list_del(&pg->list);
+		free_priority_group(pg, m->ti);
+	}
+
+	kfree(m->hw_handler_name);
+	kfree(m->hw_handler_params);
+	mutex_destroy(&m->work_mutex);
+	kfree(m);
+}
+
+static struct dm_mpath_io *get_mpio(union map_info *info)
+{
+	return info->ptr;
+}
+
+static size_t multipath_per_bio_data_size(void)
+{
+	return sizeof(struct dm_mpath_io) + sizeof(struct dm_bio_details);
+}
+
+static struct dm_mpath_io *get_mpio_from_bio(struct bio *bio)
+{
+	return dm_per_bio_data(bio, multipath_per_bio_data_size());
+}
+
+static struct dm_bio_details *get_bio_details_from_mpio(struct dm_mpath_io *mpio)
+{
+	/* dm_bio_details is immediately after the dm_mpath_io in bio's per-bio-data */
+	void *bio_details = mpio + 1;
+	return bio_details;
+}
+
+static void multipath_init_per_bio_data(struct bio *bio, struct dm_mpath_io **mpio_p)
+{
+	struct dm_mpath_io *mpio = get_mpio_from_bio(bio);
+	struct dm_bio_details *bio_details = get_bio_details_from_mpio(mpio);
+
+	mpio->nr_bytes = bio->bi_iter.bi_size;
+	mpio->pgpath = NULL;
+	mpio->start_time_ns = 0;
+	*mpio_p = mpio;
+
+	dm_bio_record(bio_details, bio);
+}
+
+/*
+ *-----------------------------------------------
+ * Path selection
+ *-----------------------------------------------
+ */
+static int __pg_init_all_paths(struct multipath *m)
+{
+	struct pgpath *pgpath;
+	unsigned long pg_init_delay = 0;
+
+	lockdep_assert_held(&m->lock);
+
+	if (atomic_read(&m->pg_init_in_progress) || test_bit(MPATHF_PG_INIT_DISABLED, &m->flags))
+		return 0;
+
+	atomic_inc(&m->pg_init_count);
+	clear_bit(MPATHF_PG_INIT_REQUIRED, &m->flags);
+
+	/* Check here to reset pg_init_required */
+	if (!m->current_pg)
+		return 0;
+
+	if (test_bit(MPATHF_PG_INIT_DELAY_RETRY, &m->flags))
+		pg_init_delay = msecs_to_jiffies(m->pg_init_delay_msecs != DM_PG_INIT_DELAY_DEFAULT ?
+						 m->pg_init_delay_msecs : DM_PG_INIT_DELAY_MSECS);
+	list_for_each_entry(pgpath, &m->current_pg->pgpaths, list) {
+		/* Skip failed paths */
+		if (!pgpath->is_active)
+			continue;
+		if (queue_delayed_work(kmpath_handlerd, &pgpath->activate_path,
+				       pg_init_delay))
+			atomic_inc(&m->pg_init_in_progress);
+	}
+	return atomic_read(&m->pg_init_in_progress);
+}
+
+static int pg_init_all_paths(struct multipath *m)
+{
+	int ret;
+	unsigned long flags;
+
+	spin_lock_irqsave(&m->lock, flags);
+	ret = __pg_init_all_paths(m);
+	spin_unlock_irqrestore(&m->lock, flags);
+
+	return ret;
+}
+
+static void __switch_pg(struct multipath *m, struct priority_group *pg)
+{
+	lockdep_assert_held(&m->lock);
+
+	m->current_pg = pg;
+
+	/* Must we initialise the PG first, and queue I/O till it's ready? */
+	if (m->hw_handler_name) {
+		set_bit(MPATHF_PG_INIT_REQUIRED, &m->flags);
+		set_bit(MPATHF_QUEUE_IO, &m->flags);
+	} else {
+		clear_bit(MPATHF_PG_INIT_REQUIRED, &m->flags);
+		clear_bit(MPATHF_QUEUE_IO, &m->flags);
+	}
+
+	atomic_set(&m->pg_init_count, 0);
+}
+
+static struct pgpath *choose_path_in_pg(struct multipath *m,
+					struct priority_group *pg,
+					size_t nr_bytes)
+{
+	unsigned long flags;
+	struct dm_path *path;
+	struct pgpath *pgpath;
+
+	path = pg->ps.type->select_path(&pg->ps, nr_bytes);
+	if (!path)
+		return ERR_PTR(-ENXIO);
+
+	pgpath = path_to_pgpath(path);
+
+	if (unlikely(READ_ONCE(m->current_pg) != pg)) {
+		/* Only update current_pgpath if pg changed */
+		spin_lock_irqsave(&m->lock, flags);
+		m->current_pgpath = pgpath;
+		__switch_pg(m, pg);
+		spin_unlock_irqrestore(&m->lock, flags);
+	}
+
+	return pgpath;
+}
+
+static struct pgpath *choose_pgpath(struct multipath *m, size_t nr_bytes)
+{
+	unsigned long flags;
+	struct priority_group *pg;
+	struct pgpath *pgpath;
+	unsigned int bypassed = 1;
+
+	if (!atomic_read(&m->nr_valid_paths)) {
+		spin_lock_irqsave(&m->lock, flags);
+		clear_bit(MPATHF_QUEUE_IO, &m->flags);
+		spin_unlock_irqrestore(&m->lock, flags);
+		goto failed;
+	}
+
+	/* Were we instructed to switch PG? */
+	if (READ_ONCE(m->next_pg)) {
+		spin_lock_irqsave(&m->lock, flags);
+		pg = m->next_pg;
+		if (!pg) {
+			spin_unlock_irqrestore(&m->lock, flags);
+			goto check_current_pg;
+		}
+		m->next_pg = NULL;
+		spin_unlock_irqrestore(&m->lock, flags);
+		pgpath = choose_path_in_pg(m, pg, nr_bytes);
+		if (!IS_ERR_OR_NULL(pgpath))
+			return pgpath;
+	}
+
+	/* Don't change PG until it has no remaining paths */
+check_current_pg:
+	pg = READ_ONCE(m->current_pg);
+	if (pg) {
+		pgpath = choose_path_in_pg(m, pg, nr_bytes);
+		if (!IS_ERR_OR_NULL(pgpath))
+			return pgpath;
+	}
+
+	/*
+	 * Loop through priority groups until we find a valid path.
+	 * First time we skip PGs marked 'bypassed'.
+	 * Second time we only try the ones we skipped, but set
+	 * pg_init_delay_retry so we do not hammer controllers.
+	 */
+	do {
+		list_for_each_entry(pg, &m->priority_groups, list) {
+			if (pg->bypassed == !!bypassed)
+				continue;
+			pgpath = choose_path_in_pg(m, pg, nr_bytes);
+			if (!IS_ERR_OR_NULL(pgpath)) {
+				if (!bypassed) {
+					spin_lock_irqsave(&m->lock, flags);
+					set_bit(MPATHF_PG_INIT_DELAY_RETRY, &m->flags);
+					spin_unlock_irqrestore(&m->lock, flags);
+				}
+				return pgpath;
+			}
+		}
+	} while (bypassed--);
+
+failed:
+	spin_lock_irqsave(&m->lock, flags);
+	m->current_pgpath = NULL;
+	m->current_pg = NULL;
+	spin_unlock_irqrestore(&m->lock, flags);
+
+	return NULL;
+}
+
+/*
+ * dm_report_EIO() is a macro instead of a function to make pr_debug_ratelimited()
+ * report the function name and line number of the function from which
+ * it has been invoked.
+ */
+#define dm_report_EIO(m)						\
+	DMDEBUG_LIMIT("%s: returning EIO; QIFNP = %d; SQIFNP = %d; DNFS = %d", \
+		      dm_table_device_name((m)->ti->table),		\
+		      test_bit(MPATHF_QUEUE_IF_NO_PATH, &(m)->flags),	\
+		      test_bit(MPATHF_SAVED_QUEUE_IF_NO_PATH, &(m)->flags), \
+		      dm_noflush_suspending((m)->ti))
+
+/*
+ * Check whether bios must be queued in the device-mapper core rather
+ * than here in the target.
+ */
+static bool __must_push_back(struct multipath *m)
+{
+	return dm_noflush_suspending(m->ti);
+}
+
+static bool must_push_back_rq(struct multipath *m)
+{
+	unsigned long flags;
+	bool ret;
+
+	spin_lock_irqsave(&m->lock, flags);
+	ret = (test_bit(MPATHF_QUEUE_IF_NO_PATH, &m->flags) || __must_push_back(m));
+	spin_unlock_irqrestore(&m->lock, flags);
+
+	return ret;
+}
+
+/*
+ * Map cloned requests (request-based multipath)
+ */
+static int multipath_clone_and_map(struct dm_target *ti, struct request *rq,
+				   union map_info *map_context,
+				   struct request **__clone)
+{
+	struct multipath *m = ti->private;
+	size_t nr_bytes = blk_rq_bytes(rq);
+	struct pgpath *pgpath;
+	struct block_device *bdev;
+	struct dm_mpath_io *mpio = get_mpio(map_context);
+	struct request_queue *q;
+	struct request *clone;
+
+	/* Do we need to select a new pgpath? */
+	pgpath = READ_ONCE(m->current_pgpath);
+	if (!pgpath || !mpath_double_check_test_bit(MPATHF_QUEUE_IO, m))
+		pgpath = choose_pgpath(m, nr_bytes);
+
+	if (!pgpath) {
+		if (must_push_back_rq(m))
+			return DM_MAPIO_DELAY_REQUEUE;
+		dm_report_EIO(m);	/* Failed */
+		return DM_MAPIO_KILL;
+	} else if (mpath_double_check_test_bit(MPATHF_QUEUE_IO, m) ||
+		   mpath_double_check_test_bit(MPATHF_PG_INIT_REQUIRED, m)) {
+		pg_init_all_paths(m);
+		return DM_MAPIO_DELAY_REQUEUE;
+	}
+
+	mpio->pgpath = pgpath;
+	mpio->nr_bytes = nr_bytes;
+
+	bdev = pgpath->path.dev->bdev;
+	q = bdev_get_queue(bdev);
+	clone = blk_mq_alloc_request(q, rq->cmd_flags | REQ_NOMERGE,
+			BLK_MQ_REQ_NOWAIT);
+	if (IS_ERR(clone)) {
+		/* EBUSY, ENODEV or EWOULDBLOCK: requeue */
+		if (blk_queue_dying(q)) {
+			atomic_inc(&m->pg_init_in_progress);
+			activate_or_offline_path(pgpath);
+			return DM_MAPIO_DELAY_REQUEUE;
+		}
+
+		/*
+		 * blk-mq's SCHED_RESTART can cover this requeue, so we
+		 * needn't deal with it by DELAY_REQUEUE. More importantly,
+		 * we have to return DM_MAPIO_REQUEUE so that blk-mq can
+		 * get the queue busy feedback (via BLK_STS_RESOURCE),
+		 * otherwise I/O merging can suffer.
+		 */
+		return DM_MAPIO_REQUEUE;
+	}
+	clone->bio = clone->biotail = NULL;
+	clone->cmd_flags |= REQ_FAILFAST_TRANSPORT;
+	*__clone = clone;
+
+	if (pgpath->pg->ps.type->start_io)
+		pgpath->pg->ps.type->start_io(&pgpath->pg->ps,
+					      &pgpath->path,
+					      nr_bytes);
+	return DM_MAPIO_REMAPPED;
+}
+
+static void multipath_release_clone(struct request *clone,
+				    union map_info *map_context)
+{
+	if (unlikely(map_context)) {
+		/*
+		 * non-NULL map_context means caller is still map
+		 * method; must undo multipath_clone_and_map()
+		 */
+		struct dm_mpath_io *mpio = get_mpio(map_context);
+		struct pgpath *pgpath = mpio->pgpath;
+
+		if (pgpath && pgpath->pg->ps.type->end_io)
+			pgpath->pg->ps.type->end_io(&pgpath->pg->ps,
+						    &pgpath->path,
+						    mpio->nr_bytes,
+						    clone->io_start_time_ns);
+	}
+
+	blk_mq_free_request(clone);
+}
+
+/*
+ * Map cloned bios (bio-based multipath)
+ */
+
+static void __multipath_queue_bio(struct multipath *m, struct bio *bio)
+{
+	/* Queue for the daemon to resubmit */
+	bio_list_add(&m->queued_bios, bio);
+	if (!test_bit(MPATHF_QUEUE_IO, &m->flags))
+		queue_work(kmultipathd, &m->process_queued_bios);
+}
+
+static void multipath_queue_bio(struct multipath *m, struct bio *bio)
+{
+	unsigned long flags;
+
+	spin_lock_irqsave(&m->lock, flags);
+	__multipath_queue_bio(m, bio);
+	spin_unlock_irqrestore(&m->lock, flags);
+}
+
+static struct pgpath *__map_bio(struct multipath *m, struct bio *bio)
+{
+	struct pgpath *pgpath;
+	unsigned long flags;
+
+	/* Do we need to select a new pgpath? */
+	pgpath = READ_ONCE(m->current_pgpath);
+	if (!pgpath || !mpath_double_check_test_bit(MPATHF_QUEUE_IO, m))
+		pgpath = choose_pgpath(m, bio->bi_iter.bi_size);
+
+	if (!pgpath) {
+		spin_lock_irqsave(&m->lock, flags);
+		if (test_bit(MPATHF_QUEUE_IF_NO_PATH, &m->flags)) {
+			__multipath_queue_bio(m, bio);
+			pgpath = ERR_PTR(-EAGAIN);
+		}
+		spin_unlock_irqrestore(&m->lock, flags);
+
+	} else if (mpath_double_check_test_bit(MPATHF_QUEUE_IO, m) ||
+		   mpath_double_check_test_bit(MPATHF_PG_INIT_REQUIRED, m)) {
+		multipath_queue_bio(m, bio);
+		pg_init_all_paths(m);
+		return ERR_PTR(-EAGAIN);
+	}
+
+	return pgpath;
+}
+
+static int __multipath_map_bio(struct multipath *m, struct bio *bio,
+			       struct dm_mpath_io *mpio)
+{
+	struct pgpath *pgpath = __map_bio(m, bio);
+
+	if (IS_ERR(pgpath))
+		return DM_MAPIO_SUBMITTED;
+
+	if (!pgpath) {
+		if (__must_push_back(m))
+			return DM_MAPIO_REQUEUE;
+		dm_report_EIO(m);
+		return DM_MAPIO_KILL;
+	}
+
+	mpio->pgpath = pgpath;
+
+	if (dm_ps_use_hr_timer(pgpath->pg->ps.type))
+		mpio->start_time_ns = ktime_get_ns();
+
+	bio->bi_status = 0;
+	bio_set_dev(bio, pgpath->path.dev->bdev);
+	bio->bi_opf |= REQ_FAILFAST_TRANSPORT;
+
+	if (pgpath->pg->ps.type->start_io)
+		pgpath->pg->ps.type->start_io(&pgpath->pg->ps,
+					      &pgpath->path,
+					      mpio->nr_bytes);
+	return DM_MAPIO_REMAPPED;
+}
+
+static int multipath_map_bio(struct dm_target *ti, struct bio *bio)
+{
+	struct multipath *m = ti->private;
+	struct dm_mpath_io *mpio = NULL;
+
+	multipath_init_per_bio_data(bio, &mpio);
+	return __multipath_map_bio(m, bio, mpio);
+}
+
+static void process_queued_io_list(struct multipath *m)
+{
+	if (m->queue_mode == DM_TYPE_REQUEST_BASED)
+		dm_mq_kick_requeue_list(dm_table_get_md(m->ti->table));
+	else if (m->queue_mode == DM_TYPE_BIO_BASED)
+		queue_work(kmultipathd, &m->process_queued_bios);
+}
+
+static void process_queued_bios(struct work_struct *work)
+{
+	int r;
+	unsigned long flags;
+	struct bio *bio;
+	struct bio_list bios;
+	struct blk_plug plug;
+	struct multipath *m =
+		container_of(work, struct multipath, process_queued_bios);
+
+	bio_list_init(&bios);
+
+	spin_lock_irqsave(&m->lock, flags);
+
+	if (bio_list_empty(&m->queued_bios)) {
+		spin_unlock_irqrestore(&m->lock, flags);
+		return;
+	}
+
+	bio_list_merge(&bios, &m->queued_bios);
+	bio_list_init(&m->queued_bios);
+
+	spin_unlock_irqrestore(&m->lock, flags);
+
+	blk_start_plug(&plug);
+	while ((bio = bio_list_pop(&bios))) {
+		struct dm_mpath_io *mpio = get_mpio_from_bio(bio);
+
+		dm_bio_restore(get_bio_details_from_mpio(mpio), bio);
+		r = __multipath_map_bio(m, bio, mpio);
+		switch (r) {
+		case DM_MAPIO_KILL:
+			bio->bi_status = BLK_STS_IOERR;
+			bio_endio(bio);
+			break;
+		case DM_MAPIO_REQUEUE:
+			bio->bi_status = BLK_STS_DM_REQUEUE;
+			bio_endio(bio);
+			break;
+		case DM_MAPIO_REMAPPED:
+			submit_bio_noacct(bio);
+			break;
+		case DM_MAPIO_SUBMITTED:
+			break;
+		default:
+			WARN_ONCE(true, "__multipath_map_bio() returned %d\n", r);
+		}
+	}
+	blk_finish_plug(&plug);
+}
+
+/*
+ * If we run out of usable paths, should we queue I/O or error it?
+ */
+static int queue_if_no_path(struct multipath *m, bool f_queue_if_no_path,
+			    bool save_old_value, const char *caller)
+{
+	unsigned long flags;
+	bool queue_if_no_path_bit, saved_queue_if_no_path_bit;
+	const char *dm_dev_name = dm_table_device_name(m->ti->table);
+
+	DMDEBUG("%s: %s caller=%s f_queue_if_no_path=%d save_old_value=%d",
+		dm_dev_name, __func__, caller, f_queue_if_no_path, save_old_value);
+
+	spin_lock_irqsave(&m->lock, flags);
+
+	queue_if_no_path_bit = test_bit(MPATHF_QUEUE_IF_NO_PATH, &m->flags);
+	saved_queue_if_no_path_bit = test_bit(MPATHF_SAVED_QUEUE_IF_NO_PATH, &m->flags);
+
+	if (save_old_value) {
+		if (unlikely(!queue_if_no_path_bit && saved_queue_if_no_path_bit)) {
+			DMERR("%s: QIFNP disabled but saved as enabled, saving again loses state, not saving!",
+			      dm_dev_name);
+		} else
+			assign_bit(MPATHF_SAVED_QUEUE_IF_NO_PATH, &m->flags, queue_if_no_path_bit);
+	} else if (!f_queue_if_no_path && saved_queue_if_no_path_bit) {
+		/* due to "fail_if_no_path" message, need to honor it. */
+		clear_bit(MPATHF_SAVED_QUEUE_IF_NO_PATH, &m->flags);
+	}
+	assign_bit(MPATHF_QUEUE_IF_NO_PATH, &m->flags, f_queue_if_no_path);
+
+	DMDEBUG("%s: after %s changes; QIFNP = %d; SQIFNP = %d; DNFS = %d",
+		dm_dev_name, __func__,
+		test_bit(MPATHF_QUEUE_IF_NO_PATH, &m->flags),
+		test_bit(MPATHF_SAVED_QUEUE_IF_NO_PATH, &m->flags),
+		dm_noflush_suspending(m->ti));
+
+	spin_unlock_irqrestore(&m->lock, flags);
+
+	if (!f_queue_if_no_path) {
+		dm_table_run_md_queue_async(m->ti->table);
+		process_queued_io_list(m);
+	}
+
+	return 0;
+}
+
+/*
+ * If the queue_if_no_path timeout fires, turn off queue_if_no_path and
+ * process any queued I/O.
+ */
+static void queue_if_no_path_timeout_work(struct timer_list *t)
+{
+	struct multipath *m = from_timer(m, t, nopath_timer);
+
+	DMWARN("queue_if_no_path timeout on %s, failing queued IO",
+	       dm_table_device_name(m->ti->table));
+	queue_if_no_path(m, false, false, __func__);
+}
+
+/*
+ * Enable the queue_if_no_path timeout if necessary.
+ * Called with m->lock held.
+ */
+static void enable_nopath_timeout(struct multipath *m)
+{
+	unsigned long queue_if_no_path_timeout =
+		READ_ONCE(queue_if_no_path_timeout_secs) * HZ;
+
+	lockdep_assert_held(&m->lock);
+
+	if (queue_if_no_path_timeout > 0 &&
+	    atomic_read(&m->nr_valid_paths) == 0 &&
+	    test_bit(MPATHF_QUEUE_IF_NO_PATH, &m->flags)) {
+		mod_timer(&m->nopath_timer,
+			  jiffies + queue_if_no_path_timeout);
+	}
+}
+
+static void disable_nopath_timeout(struct multipath *m)
+{
+	del_timer_sync(&m->nopath_timer);
+}
+
+/*
+ * An event is triggered whenever a path is taken out of use.
+ * Includes path failure and PG bypass.
+ */
+static void trigger_event(struct work_struct *work)
+{
+	struct multipath *m =
+		container_of(work, struct multipath, trigger_event);
+
+	dm_table_event(m->ti->table);
+}
+
+/*
+ *---------------------------------------------------------------
+ * Constructor/argument parsing:
+ * <#multipath feature args> [<arg>]*
+ * <#hw_handler args> [hw_handler [<arg>]*]
+ * <#priority groups>
+ * <initial priority group>
+ *     [<selector> <#selector args> [<arg>]*
+ *      <#paths> <#per-path selector args>
+ *         [<path> [<arg>]* ]+ ]+
+ *---------------------------------------------------------------
+ */
+static int parse_path_selector(struct dm_arg_set *as, struct priority_group *pg,
+			       struct dm_target *ti)
+{
+	int r;
+	struct path_selector_type *pst;
+	unsigned int ps_argc;
+
+	static const struct dm_arg _args[] = {
+		{0, 1024, "invalid number of path selector args"},
+	};
+
+	pst = dm_get_path_selector(dm_shift_arg(as));
+	if (!pst) {
+		ti->error = "unknown path selector type";
+		return -EINVAL;
+	}
+
+	r = dm_read_arg_group(_args, as, &ps_argc, &ti->error);
+	if (r) {
+		dm_put_path_selector(pst);
+		return -EINVAL;
+	}
+
+	r = pst->create(&pg->ps, ps_argc, as->argv);
+	if (r) {
+		dm_put_path_selector(pst);
+		ti->error = "path selector constructor failed";
+		return r;
+	}
+
+	pg->ps.type = pst;
+	dm_consume_args(as, ps_argc);
+
+	return 0;
+}
+
+static int setup_scsi_dh(struct block_device *bdev, struct multipath *m,
+			 const char **attached_handler_name, char **error)
+{
+	struct request_queue *q = bdev_get_queue(bdev);
+	int r;
+
+	if (mpath_double_check_test_bit(MPATHF_RETAIN_ATTACHED_HW_HANDLER, m)) {
+retain:
+		if (*attached_handler_name) {
+			/*
+			 * Clear any hw_handler_params associated with a
+			 * handler that isn't already attached.
+			 */
+			if (m->hw_handler_name && strcmp(*attached_handler_name, m->hw_handler_name)) {
+				kfree(m->hw_handler_params);
+				m->hw_handler_params = NULL;
+			}
+
+			/*
+			 * Reset hw_handler_name to match the attached handler
+			 *
+			 * NB. This modifies the table line to show the actual
+			 * handler instead of the original table passed in.
+			 */
+			kfree(m->hw_handler_name);
+			m->hw_handler_name = *attached_handler_name;
+			*attached_handler_name = NULL;
+		}
+	}
+
+	if (m->hw_handler_name) {
+		r = scsi_dh_attach(q, m->hw_handler_name);
+		if (r == -EBUSY) {
+			DMINFO("retaining handler on device %pg", bdev);
+			goto retain;
+		}
+		if (r < 0) {
+			*error = "error attaching hardware handler";
+			return r;
+		}
+
+		if (m->hw_handler_params) {
+			r = scsi_dh_set_params(q, m->hw_handler_params);
+			if (r < 0) {
+				*error = "unable to set hardware handler parameters";
+				return r;
+			}
+		}
+	}
+
+	return 0;
+}
+
+static struct pgpath *parse_path(struct dm_arg_set *as, struct path_selector *ps,
+				 struct dm_target *ti)
+{
+	int r;
+	struct pgpath *p;
+	struct multipath *m = ti->private;
+	struct request_queue *q;
+	const char *attached_handler_name = NULL;
+
+	/* we need at least a path arg */
+	if (as->argc < 1) {
+		ti->error = "no device given";
+		return ERR_PTR(-EINVAL);
+	}
+
+	p = alloc_pgpath();
+	if (!p)
+		return ERR_PTR(-ENOMEM);
+
+	r = dm_get_device(ti, dm_shift_arg(as), dm_table_get_mode(ti->table),
+			  &p->path.dev);
+	if (r) {
+		ti->error = "error getting device";
+		goto bad;
+	}
+
+	q = bdev_get_queue(p->path.dev->bdev);
+	attached_handler_name = scsi_dh_attached_handler_name(q, GFP_KERNEL);
+	if (attached_handler_name || m->hw_handler_name) {
+		INIT_DELAYED_WORK(&p->activate_path, activate_path_work);
+		r = setup_scsi_dh(p->path.dev->bdev, m, &attached_handler_name, &ti->error);
+		kfree(attached_handler_name);
+		if (r) {
+			dm_put_device(ti, p->path.dev);
+			goto bad;
+		}
+	}
+
+	r = ps->type->add_path(ps, &p->path, as->argc, as->argv, &ti->error);
+	if (r) {
+		dm_put_device(ti, p->path.dev);
+		goto bad;
+	}
+
+	return p;
+ bad:
+	free_pgpath(p);
+	return ERR_PTR(r);
+}
+
+static struct priority_group *parse_priority_group(struct dm_arg_set *as,
+						   struct multipath *m)
+{
+	static const struct dm_arg _args[] = {
+		{1, 1024, "invalid number of paths"},
+		{0, 1024, "invalid number of selector args"}
+	};
+
+	int r;
+	unsigned int i, nr_selector_args, nr_args;
+	struct priority_group *pg;
+	struct dm_target *ti = m->ti;
+
+	if (as->argc < 2) {
+		as->argc = 0;
+		ti->error = "not enough priority group arguments";
+		return ERR_PTR(-EINVAL);
+	}
+
+	pg = alloc_priority_group();
+	if (!pg) {
+		ti->error = "couldn't allocate priority group";
+		return ERR_PTR(-ENOMEM);
+	}
+	pg->m = m;
+
+	r = parse_path_selector(as, pg, ti);
+	if (r)
+		goto bad;
+
+	/*
+	 * read the paths
+	 */
+	r = dm_read_arg(_args, as, &pg->nr_pgpaths, &ti->error);
+	if (r)
+		goto bad;
+
+	r = dm_read_arg(_args + 1, as, &nr_selector_args, &ti->error);
+	if (r)
+		goto bad;
+
+	nr_args = 1 + nr_selector_args;
+	for (i = 0; i < pg->nr_pgpaths; i++) {
+		struct pgpath *pgpath;
+		struct dm_arg_set path_args;
+
+		if (as->argc < nr_args) {
+			ti->error = "not enough path parameters";
+			r = -EINVAL;
+			goto bad;
+		}
+
+		path_args.argc = nr_args;
+		path_args.argv = as->argv;
+
+		pgpath = parse_path(&path_args, &pg->ps, ti);
+		if (IS_ERR(pgpath)) {
+			r = PTR_ERR(pgpath);
+			goto bad;
+		}
+
+		pgpath->pg = pg;
+		list_add_tail(&pgpath->list, &pg->pgpaths);
+		dm_consume_args(as, nr_args);
+	}
+
+	return pg;
+
+ bad:
+	free_priority_group(pg, ti);
+	return ERR_PTR(r);
+}
+
+static int parse_hw_handler(struct dm_arg_set *as, struct multipath *m)
+{
+	unsigned int hw_argc;
+	int ret;
+	struct dm_target *ti = m->ti;
+
+	static const struct dm_arg _args[] = {
+		{0, 1024, "invalid number of hardware handler args"},
+	};
+
+	if (dm_read_arg_group(_args, as, &hw_argc, &ti->error))
+		return -EINVAL;
+
+	if (!hw_argc)
+		return 0;
+
+	if (m->queue_mode == DM_TYPE_BIO_BASED) {
+		dm_consume_args(as, hw_argc);
+		DMERR("bio-based multipath doesn't allow hardware handler args");
+		return 0;
+	}
+
+	m->hw_handler_name = kstrdup(dm_shift_arg(as), GFP_KERNEL);
+	if (!m->hw_handler_name)
+		return -EINVAL;
+
+	if (hw_argc > 1) {
+		char *p;
+		int i, j, len = 4;
+
+		for (i = 0; i <= hw_argc - 2; i++)
+			len += strlen(as->argv[i]) + 1;
+		p = m->hw_handler_params = kzalloc(len, GFP_KERNEL);
+		if (!p) {
+			ti->error = "memory allocation failed";
+			ret = -ENOMEM;
+			goto fail;
+		}
+		j = sprintf(p, "%d", hw_argc - 1);
+		for (i = 0, p += j + 1; i <= hw_argc - 2; i++, p += j + 1)
+			j = sprintf(p, "%s", as->argv[i]);
+	}
+	dm_consume_args(as, hw_argc - 1);
+
+	return 0;
+fail:
+	kfree(m->hw_handler_name);
+	m->hw_handler_name = NULL;
+	return ret;
+}
+
+static int parse_features(struct dm_arg_set *as, struct multipath *m)
+{
+	int r;
+	unsigned int argc;
+	struct dm_target *ti = m->ti;
+	const char *arg_name;
+
+	static const struct dm_arg _args[] = {
+		{0, 8, "invalid number of feature args"},
+		{1, 50, "pg_init_retries must be between 1 and 50"},
+		{0, 60000, "pg_init_delay_msecs must be between 0 and 60000"},
+	};
+
+	r = dm_read_arg_group(_args, as, &argc, &ti->error);
+	if (r)
+		return -EINVAL;
+
+	if (!argc)
+		return 0;
+
+	do {
+		arg_name = dm_shift_arg(as);
+		argc--;
+
+		if (!strcasecmp(arg_name, "queue_if_no_path")) {
+			r = queue_if_no_path(m, true, false, __func__);
+			continue;
+		}
+
+		if (!strcasecmp(arg_name, "retain_attached_hw_handler")) {
+			set_bit(MPATHF_RETAIN_ATTACHED_HW_HANDLER, &m->flags);
+			continue;
+		}
+
+		if (!strcasecmp(arg_name, "pg_init_retries") &&
+		    (argc >= 1)) {
+			r = dm_read_arg(_args + 1, as, &m->pg_init_retries, &ti->error);
+			argc--;
+			continue;
+		}
+
+		if (!strcasecmp(arg_name, "pg_init_delay_msecs") &&
+		    (argc >= 1)) {
+			r = dm_read_arg(_args + 2, as, &m->pg_init_delay_msecs, &ti->error);
+			argc--;
+			continue;
+		}
+
+		if (!strcasecmp(arg_name, "queue_mode") &&
+		    (argc >= 1)) {
+			const char *queue_mode_name = dm_shift_arg(as);
+
+			if (!strcasecmp(queue_mode_name, "bio"))
+				m->queue_mode = DM_TYPE_BIO_BASED;
+			else if (!strcasecmp(queue_mode_name, "rq") ||
+				 !strcasecmp(queue_mode_name, "mq"))
+				m->queue_mode = DM_TYPE_REQUEST_BASED;
+			else {
+				ti->error = "Unknown 'queue_mode' requested";
+				r = -EINVAL;
+			}
+			argc--;
+			continue;
+		}
+
+		ti->error = "Unrecognised multipath feature request";
+		r = -EINVAL;
+	} while (argc && !r);
+
+	return r;
+}
+
+static int multipath_ctr(struct dm_target *ti, unsigned int argc, char **argv)
+{
+	/* target arguments */
+	static const struct dm_arg _args[] = {
+		{0, 1024, "invalid number of priority groups"},
+		{0, 1024, "invalid initial priority group number"},
+	};
+
+	int r;
+	struct multipath *m;
+	struct dm_arg_set as;
+	unsigned int pg_count = 0;
+	unsigned int next_pg_num;
+	unsigned long flags;
+
+	as.argc = argc;
+	as.argv = argv;
+
+	m = alloc_multipath(ti);
+	if (!m) {
+		ti->error = "can't allocate multipath";
+		return -EINVAL;
+	}
+
+	r = parse_features(&as, m);
+	if (r)
+		goto bad;
+
+	r = alloc_multipath_stage2(ti, m);
+	if (r)
+		goto bad;
+
+	r = parse_hw_handler(&as, m);
+	if (r)
+		goto bad;
+
+	r = dm_read_arg(_args, &as, &m->nr_priority_groups, &ti->error);
+	if (r)
+		goto bad;
+
+	r = dm_read_arg(_args + 1, &as, &next_pg_num, &ti->error);
+	if (r)
+		goto bad;
+
+	if ((!m->nr_priority_groups && next_pg_num) ||
+	    (m->nr_priority_groups && !next_pg_num)) {
+		ti->error = "invalid initial priority group";
+		r = -EINVAL;
+		goto bad;
+	}
+
+	/* parse the priority groups */
+	while (as.argc) {
+		struct priority_group *pg;
+		unsigned int nr_valid_paths = atomic_read(&m->nr_valid_paths);
+
+		pg = parse_priority_group(&as, m);
+		if (IS_ERR(pg)) {
+			r = PTR_ERR(pg);
+			goto bad;
+		}
+
+		nr_valid_paths += pg->nr_pgpaths;
+		atomic_set(&m->nr_valid_paths, nr_valid_paths);
+
+		list_add_tail(&pg->list, &m->priority_groups);
+		pg_count++;
+		pg->pg_num = pg_count;
+		if (!--next_pg_num)
+			m->next_pg = pg;
+	}
+
+	if (pg_count != m->nr_priority_groups) {
+		ti->error = "priority group count mismatch";
+		r = -EINVAL;
+		goto bad;
+	}
+
+	spin_lock_irqsave(&m->lock, flags);
+	enable_nopath_timeout(m);
+	spin_unlock_irqrestore(&m->lock, flags);
+
+	ti->num_flush_bios = 1;
+	ti->num_discard_bios = 1;
+	ti->num_write_zeroes_bios = 1;
+	if (m->queue_mode == DM_TYPE_BIO_BASED)
+		ti->per_io_data_size = multipath_per_bio_data_size();
+	else
+		ti->per_io_data_size = sizeof(struct dm_mpath_io);
+
+	return 0;
+
+ bad:
+	free_multipath(m);
+	return r;
+}
+
+static void multipath_wait_for_pg_init_completion(struct multipath *m)
+{
+	DEFINE_WAIT(wait);
+
+	while (1) {
+		prepare_to_wait(&m->pg_init_wait, &wait, TASK_UNINTERRUPTIBLE);
+
+		if (!atomic_read(&m->pg_init_in_progress))
+			break;
+
+		io_schedule();
+	}
+	finish_wait(&m->pg_init_wait, &wait);
+}
+
+static void flush_multipath_work(struct multipath *m)
+{
+	if (m->hw_handler_name) {
+		unsigned long flags;
+
+		if (!atomic_read(&m->pg_init_in_progress))
+			goto skip;
+
+		spin_lock_irqsave(&m->lock, flags);
+		if (atomic_read(&m->pg_init_in_progress) &&
+		    !test_and_set_bit(MPATHF_PG_INIT_DISABLED, &m->flags)) {
+			spin_unlock_irqrestore(&m->lock, flags);
+
+			flush_workqueue(kmpath_handlerd);
+			multipath_wait_for_pg_init_completion(m);
+
+			spin_lock_irqsave(&m->lock, flags);
+			clear_bit(MPATHF_PG_INIT_DISABLED, &m->flags);
+		}
+		spin_unlock_irqrestore(&m->lock, flags);
+	}
+skip:
+	if (m->queue_mode == DM_TYPE_BIO_BASED)
+		flush_work(&m->process_queued_bios);
+	flush_work(&m->trigger_event);
+}
+
+static void multipath_dtr(struct dm_target *ti)
+{
+	struct multipath *m = ti->private;
+
+	disable_nopath_timeout(m);
+	flush_multipath_work(m);
+	free_multipath(m);
+}
+
+/*
+ * Take a path out of use.
+ */
+static int fail_path(struct pgpath *pgpath)
+{
+	unsigned long flags;
+	struct multipath *m = pgpath->pg->m;
+
+	spin_lock_irqsave(&m->lock, flags);
+
+	if (!pgpath->is_active)
+		goto out;
+
+	DMWARN("%s: Failing path %s.",
+	       dm_table_device_name(m->ti->table),
+	       pgpath->path.dev->name);
+
+	pgpath->pg->ps.type->fail_path(&pgpath->pg->ps, &pgpath->path);
+	pgpath->is_active = false;
+	pgpath->fail_count++;
+
+	atomic_dec(&m->nr_valid_paths);
+
+	if (pgpath == m->current_pgpath)
+		m->current_pgpath = NULL;
+
+	dm_path_uevent(DM_UEVENT_PATH_FAILED, m->ti,
+		       pgpath->path.dev->name, atomic_read(&m->nr_valid_paths));
+
+	queue_work(dm_mpath_wq, &m->trigger_event);
+
+	enable_nopath_timeout(m);
+
+out:
+	spin_unlock_irqrestore(&m->lock, flags);
+
+	return 0;
+}
+
+/*
+ * Reinstate a previously-failed path
+ */
+static int reinstate_path(struct pgpath *pgpath)
+{
+	int r = 0, run_queue = 0;
+	unsigned long flags;
+	struct multipath *m = pgpath->pg->m;
+	unsigned int nr_valid_paths;
+
+	spin_lock_irqsave(&m->lock, flags);
+
+	if (pgpath->is_active)
+		goto out;
+
+	DMWARN("%s: Reinstating path %s.",
+	       dm_table_device_name(m->ti->table),
+	       pgpath->path.dev->name);
+
+	r = pgpath->pg->ps.type->reinstate_path(&pgpath->pg->ps, &pgpath->path);
+	if (r)
+		goto out;
+
+	pgpath->is_active = true;
+
+	nr_valid_paths = atomic_inc_return(&m->nr_valid_paths);
+	if (nr_valid_paths == 1) {
+		m->current_pgpath = NULL;
+		run_queue = 1;
+	} else if (m->hw_handler_name && (m->current_pg == pgpath->pg)) {
+		if (queue_work(kmpath_handlerd, &pgpath->activate_path.work))
+			atomic_inc(&m->pg_init_in_progress);
+	}
+
+	dm_path_uevent(DM_UEVENT_PATH_REINSTATED, m->ti,
+		       pgpath->path.dev->name, nr_valid_paths);
+
+	schedule_work(&m->trigger_event);
+
+out:
+	spin_unlock_irqrestore(&m->lock, flags);
+	if (run_queue) {
+		dm_table_run_md_queue_async(m->ti->table);
+		process_queued_io_list(m);
+	}
+
+	if (pgpath->is_active)
+		disable_nopath_timeout(m);
+
+	return r;
+}
+
+/*
+ * Fail or reinstate all paths that match the provided struct dm_dev.
+ */
+static int action_dev(struct multipath *m, struct dm_dev *dev,
+		      action_fn action)
+{
+	int r = -EINVAL;
+	struct pgpath *pgpath;
+	struct priority_group *pg;
+
+	list_for_each_entry(pg, &m->priority_groups, list) {
+		list_for_each_entry(pgpath, &pg->pgpaths, list) {
+			if (pgpath->path.dev == dev)
+				r = action(pgpath);
+		}
+	}
+
+	return r;
+}
+
+/*
+ * Temporarily try to avoid having to use the specified PG
+ */
+static void bypass_pg(struct multipath *m, struct priority_group *pg,
+		      bool bypassed)
+{
+	unsigned long flags;
+
+	spin_lock_irqsave(&m->lock, flags);
+
+	pg->bypassed = bypassed;
+	m->current_pgpath = NULL;
+	m->current_pg = NULL;
+
+	spin_unlock_irqrestore(&m->lock, flags);
+
+	schedule_work(&m->trigger_event);
+}
+
+/*
+ * Switch to using the specified PG from the next I/O that gets mapped
+ */
+static int switch_pg_num(struct multipath *m, const char *pgstr)
+{
+	struct priority_group *pg;
+	unsigned int pgnum;
+	unsigned long flags;
+	char dummy;
+
+	if (!pgstr || (sscanf(pgstr, "%u%c", &pgnum, &dummy) != 1) || !pgnum ||
+	    !m->nr_priority_groups || (pgnum > m->nr_priority_groups)) {
+		DMWARN("invalid PG number supplied to %s", __func__);
+		return -EINVAL;
+	}
+
+	spin_lock_irqsave(&m->lock, flags);
+	list_for_each_entry(pg, &m->priority_groups, list) {
+		pg->bypassed = false;
+		if (--pgnum)
+			continue;
+
+		m->current_pgpath = NULL;
+		m->current_pg = NULL;
+		m->next_pg = pg;
+	}
+	spin_unlock_irqrestore(&m->lock, flags);
+
+	schedule_work(&m->trigger_event);
+	return 0;
+}
+
+/*
+ * Set/clear bypassed status of a PG.
+ * PGs are numbered upwards from 1 in the order they were declared.
+ */
+static int bypass_pg_num(struct multipath *m, const char *pgstr, bool bypassed)
+{
+	struct priority_group *pg;
+	unsigned int pgnum;
+	char dummy;
+
+	if (!pgstr || (sscanf(pgstr, "%u%c", &pgnum, &dummy) != 1) || !pgnum ||
+	    !m->nr_priority_groups || (pgnum > m->nr_priority_groups)) {
+		DMWARN("invalid PG number supplied to bypass_pg");
+		return -EINVAL;
+	}
+
+	list_for_each_entry(pg, &m->priority_groups, list) {
+		if (!--pgnum)
+			break;
+	}
+
+	bypass_pg(m, pg, bypassed);
+	return 0;
+}
+
+/*
+ * Should we retry pg_init immediately?
+ */
+static bool pg_init_limit_reached(struct multipath *m, struct pgpath *pgpath)
+{
+	unsigned long flags;
+	bool limit_reached = false;
+
+	spin_lock_irqsave(&m->lock, flags);
+
+	if (atomic_read(&m->pg_init_count) <= m->pg_init_retries &&
+	    !test_bit(MPATHF_PG_INIT_DISABLED, &m->flags))
+		set_bit(MPATHF_PG_INIT_REQUIRED, &m->flags);
+	else
+		limit_reached = true;
+
+	spin_unlock_irqrestore(&m->lock, flags);
+
+	return limit_reached;
+}
+
+static void pg_init_done(void *data, int errors)
+{
+	struct pgpath *pgpath = data;
+	struct priority_group *pg = pgpath->pg;
+	struct multipath *m = pg->m;
+	unsigned long flags;
+	bool delay_retry = false;
+
+	/* device or driver problems */
+	switch (errors) {
+	case SCSI_DH_OK:
+		break;
+	case SCSI_DH_NOSYS:
+		if (!m->hw_handler_name) {
+			errors = 0;
+			break;
+		}
+		DMERR("Could not failover the device: Handler scsi_dh_%s "
+		      "Error %d.", m->hw_handler_name, errors);
+		/*
+		 * Fail path for now, so we do not ping pong
+		 */
+		fail_path(pgpath);
+		break;
+	case SCSI_DH_DEV_TEMP_BUSY:
+		/*
+		 * Probably doing something like FW upgrade on the
+		 * controller so try the other pg.
+		 */
+		bypass_pg(m, pg, true);
+		break;
+	case SCSI_DH_RETRY:
+		/* Wait before retrying. */
+		delay_retry = true;
+		fallthrough;
+	case SCSI_DH_IMM_RETRY:
+	case SCSI_DH_RES_TEMP_UNAVAIL:
+		if (pg_init_limit_reached(m, pgpath))
+			fail_path(pgpath);
+		errors = 0;
+		break;
+	case SCSI_DH_DEV_OFFLINED:
+	default:
+		/*
+		 * We probably do not want to fail the path for a device
+		 * error, but this is what the old dm did. In future
+		 * patches we can do more advanced handling.
+		 */
+		fail_path(pgpath);
+	}
+
+	spin_lock_irqsave(&m->lock, flags);
+	if (errors) {
+		if (pgpath == m->current_pgpath) {
+			DMERR("Could not failover device. Error %d.", errors);
+			m->current_pgpath = NULL;
+			m->current_pg = NULL;
+		}
+	} else if (!test_bit(MPATHF_PG_INIT_REQUIRED, &m->flags))
+		pg->bypassed = false;
+
+	if (atomic_dec_return(&m->pg_init_in_progress) > 0)
+		/* Activations of other paths are still on going */
+		goto out;
+
+	if (test_bit(MPATHF_PG_INIT_REQUIRED, &m->flags)) {
+		if (delay_retry)
+			set_bit(MPATHF_PG_INIT_DELAY_RETRY, &m->flags);
+		else
+			clear_bit(MPATHF_PG_INIT_DELAY_RETRY, &m->flags);
+
+		if (__pg_init_all_paths(m))
+			goto out;
+	}
+	clear_bit(MPATHF_QUEUE_IO, &m->flags);
+
+	process_queued_io_list(m);
+
+	/*
+	 * Wake up any thread waiting to suspend.
+	 */
+	wake_up(&m->pg_init_wait);
+
+out:
+	spin_unlock_irqrestore(&m->lock, flags);
+}
+
+static void activate_or_offline_path(struct pgpath *pgpath)
+{
+	struct request_queue *q = bdev_get_queue(pgpath->path.dev->bdev);
+
+	if (pgpath->is_active && !blk_queue_dying(q))
+		scsi_dh_activate(q, pg_init_done, pgpath);
+	else
+		pg_init_done(pgpath, SCSI_DH_DEV_OFFLINED);
+}
+
+static void activate_path_work(struct work_struct *work)
+{
+	struct pgpath *pgpath =
+		container_of(work, struct pgpath, activate_path.work);
+
+	activate_or_offline_path(pgpath);
+}
+
+static int multipath_end_io(struct dm_target *ti, struct request *clone,
+			    blk_status_t error, union map_info *map_context)
+{
+	struct dm_mpath_io *mpio = get_mpio(map_context);
+	struct pgpath *pgpath = mpio->pgpath;
+	int r = DM_ENDIO_DONE;
+
+	/*
+	 * We don't queue any clone request inside the multipath target
+	 * during end I/O handling, since those clone requests don't have
+	 * bio clones.  If we queue them inside the multipath target,
+	 * we need to make bio clones, that requires memory allocation.
+	 * (See drivers/md/dm-rq.c:end_clone_bio() about why the clone requests
+	 *  don't have bio clones.)
+	 * Instead of queueing the clone request here, we queue the original
+	 * request into dm core, which will remake a clone request and
+	 * clone bios for it and resubmit it later.
+	 */
+	if (error && blk_path_error(error)) {
+		struct multipath *m = ti->private;
+
+		if (error == BLK_STS_RESOURCE)
+			r = DM_ENDIO_DELAY_REQUEUE;
+		else
+			r = DM_ENDIO_REQUEUE;
+
+		if (pgpath)
+			fail_path(pgpath);
+
+		if (!atomic_read(&m->nr_valid_paths) &&
+		    !must_push_back_rq(m)) {
+			if (error == BLK_STS_IOERR)
+				dm_report_EIO(m);
+			/* complete with the original error */
+			r = DM_ENDIO_DONE;
+		}
+	}
+
+	if (pgpath) {
+		struct path_selector *ps = &pgpath->pg->ps;
+
+		if (ps->type->end_io)
+			ps->type->end_io(ps, &pgpath->path, mpio->nr_bytes,
+					 clone->io_start_time_ns);
+	}
+
+	return r;
+}
+
+static int multipath_end_io_bio(struct dm_target *ti, struct bio *clone,
+				blk_status_t *error)
+{
+	struct multipath *m = ti->private;
+	struct dm_mpath_io *mpio = get_mpio_from_bio(clone);
+	struct pgpath *pgpath = mpio->pgpath;
+	unsigned long flags;
+	int r = DM_ENDIO_DONE;
+
+	if (!*error || !blk_path_error(*error))
+		goto done;
+
+	if (pgpath)
+		fail_path(pgpath);
+
+	if (!atomic_read(&m->nr_valid_paths)) {
+		spin_lock_irqsave(&m->lock, flags);
+		if (!test_bit(MPATHF_QUEUE_IF_NO_PATH, &m->flags)) {
+			if (__must_push_back(m)) {
+				r = DM_ENDIO_REQUEUE;
+			} else {
+				dm_report_EIO(m);
+				*error = BLK_STS_IOERR;
+			}
+			spin_unlock_irqrestore(&m->lock, flags);
+			goto done;
+		}
+		spin_unlock_irqrestore(&m->lock, flags);
+	}
+
+	multipath_queue_bio(m, clone);
+	r = DM_ENDIO_INCOMPLETE;
+done:
+	if (pgpath) {
+		struct path_selector *ps = &pgpath->pg->ps;
+
+		if (ps->type->end_io)
+			ps->type->end_io(ps, &pgpath->path, mpio->nr_bytes,
+					 (mpio->start_time_ns ?:
+					  dm_start_time_ns_from_clone(clone)));
+	}
+
+	return r;
+}
+
+/*
+ * Suspend with flush can't complete until all the I/O is processed
+ * so if the last path fails we must error any remaining I/O.
+ * - Note that if the freeze_bdev fails while suspending, the
+ *   queue_if_no_path state is lost - userspace should reset it.
+ * Otherwise, during noflush suspend, queue_if_no_path will not change.
+ */
+static void multipath_presuspend(struct dm_target *ti)
+{
+	struct multipath *m = ti->private;
+
+	/* FIXME: bio-based shouldn't need to always disable queue_if_no_path */
+	if (m->queue_mode == DM_TYPE_BIO_BASED || !dm_noflush_suspending(m->ti))
+		queue_if_no_path(m, false, true, __func__);
+}
+
+static void multipath_postsuspend(struct dm_target *ti)
+{
+	struct multipath *m = ti->private;
+
+	mutex_lock(&m->work_mutex);
+	flush_multipath_work(m);
+	mutex_unlock(&m->work_mutex);
+}
+
+/*
+ * Restore the queue_if_no_path setting.
+ */
+static void multipath_resume(struct dm_target *ti)
+{
+	struct multipath *m = ti->private;
+	unsigned long flags;
+
+	spin_lock_irqsave(&m->lock, flags);
+	if (test_bit(MPATHF_SAVED_QUEUE_IF_NO_PATH, &m->flags)) {
+		set_bit(MPATHF_QUEUE_IF_NO_PATH, &m->flags);
+		clear_bit(MPATHF_SAVED_QUEUE_IF_NO_PATH, &m->flags);
+	}
+
+	DMDEBUG("%s: %s finished; QIFNP = %d; SQIFNP = %d",
+		dm_table_device_name(m->ti->table), __func__,
+		test_bit(MPATHF_QUEUE_IF_NO_PATH, &m->flags),
+		test_bit(MPATHF_SAVED_QUEUE_IF_NO_PATH, &m->flags));
+
+	spin_unlock_irqrestore(&m->lock, flags);
+}
+
+/*
+ * Info output has the following format:
+ * num_multipath_feature_args [multipath_feature_args]*
+ * num_handler_status_args [handler_status_args]*
+ * num_groups init_group_number
+ *            [A|D|E num_ps_status_args [ps_status_args]*
+ *             num_paths num_selector_args
+ *             [path_dev A|F fail_count [selector_args]* ]+ ]+
+ *
+ * Table output has the following format (identical to the constructor string):
+ * num_feature_args [features_args]*
+ * num_handler_args hw_handler [hw_handler_args]*
+ * num_groups init_group_number
+ *     [priority selector-name num_ps_args [ps_args]*
+ *      num_paths num_selector_args [path_dev [selector_args]* ]+ ]+
+ */
+static void multipath_status(struct dm_target *ti, status_type_t type,
+			     unsigned int status_flags, char *result, unsigned int maxlen)
+{
+	int sz = 0, pg_counter, pgpath_counter;
+	unsigned long flags;
+	struct multipath *m = ti->private;
+	struct priority_group *pg;
+	struct pgpath *p;
+	unsigned int pg_num;
+	char state;
+
+	spin_lock_irqsave(&m->lock, flags);
+
+	/* Features */
+	if (type == STATUSTYPE_INFO)
+		DMEMIT("2 %u %u ", test_bit(MPATHF_QUEUE_IO, &m->flags),
+		       atomic_read(&m->pg_init_count));
+	else {
+		DMEMIT("%u ", test_bit(MPATHF_QUEUE_IF_NO_PATH, &m->flags) +
+			      (m->pg_init_retries > 0) * 2 +
+			      (m->pg_init_delay_msecs != DM_PG_INIT_DELAY_DEFAULT) * 2 +
+			      test_bit(MPATHF_RETAIN_ATTACHED_HW_HANDLER, &m->flags) +
+			      (m->queue_mode != DM_TYPE_REQUEST_BASED) * 2);
+
+		if (test_bit(MPATHF_QUEUE_IF_NO_PATH, &m->flags))
+			DMEMIT("queue_if_no_path ");
+		if (m->pg_init_retries)
+			DMEMIT("pg_init_retries %u ", m->pg_init_retries);
+		if (m->pg_init_delay_msecs != DM_PG_INIT_DELAY_DEFAULT)
+			DMEMIT("pg_init_delay_msecs %u ", m->pg_init_delay_msecs);
+		if (test_bit(MPATHF_RETAIN_ATTACHED_HW_HANDLER, &m->flags))
+			DMEMIT("retain_attached_hw_handler ");
+		if (m->queue_mode != DM_TYPE_REQUEST_BASED) {
+			switch (m->queue_mode) {
+			case DM_TYPE_BIO_BASED:
+				DMEMIT("queue_mode bio ");
+				break;
+			default:
+				WARN_ON_ONCE(true);
+				break;
+			}
+		}
+	}
+
+	if (!m->hw_handler_name || type == STATUSTYPE_INFO)
+		DMEMIT("0 ");
+	else
+		DMEMIT("1 %s ", m->hw_handler_name);
+
+	DMEMIT("%u ", m->nr_priority_groups);
+
+	if (m->next_pg)
+		pg_num = m->next_pg->pg_num;
+	else if (m->current_pg)
+		pg_num = m->current_pg->pg_num;
+	else
+		pg_num = (m->nr_priority_groups ? 1 : 0);
+
+	DMEMIT("%u ", pg_num);
+
+	switch (type) {
+	case STATUSTYPE_INFO:
+		list_for_each_entry(pg, &m->priority_groups, list) {
+			if (pg->bypassed)
+				state = 'D';	/* Disabled */
+			else if (pg == m->current_pg)
+				state = 'A';	/* Currently Active */
+			else
+				state = 'E';	/* Enabled */
+
+			DMEMIT("%c ", state);
+
+			if (pg->ps.type->status)
+				sz += pg->ps.type->status(&pg->ps, NULL, type,
+							  result + sz,
+							  maxlen - sz);
+			else
+				DMEMIT("0 ");
+
+			DMEMIT("%u %u ", pg->nr_pgpaths,
+			       pg->ps.type->info_args);
+
+			list_for_each_entry(p, &pg->pgpaths, list) {
+				DMEMIT("%s %s %u ", p->path.dev->name,
+				       p->is_active ? "A" : "F",
+				       p->fail_count);
+				if (pg->ps.type->status)
+					sz += pg->ps.type->status(&pg->ps,
+					      &p->path, type, result + sz,
+					      maxlen - sz);
+			}
+		}
+		break;
+
+	case STATUSTYPE_TABLE:
+		list_for_each_entry(pg, &m->priority_groups, list) {
+			DMEMIT("%s ", pg->ps.type->name);
+
+			if (pg->ps.type->status)
+				sz += pg->ps.type->status(&pg->ps, NULL, type,
+							  result + sz,
+							  maxlen - sz);
+			else
+				DMEMIT("0 ");
+
+			DMEMIT("%u %u ", pg->nr_pgpaths,
+			       pg->ps.type->table_args);
+
+			list_for_each_entry(p, &pg->pgpaths, list) {
+				DMEMIT("%s ", p->path.dev->name);
+				if (pg->ps.type->status)
+					sz += pg->ps.type->status(&pg->ps,
+					      &p->path, type, result + sz,
+					      maxlen - sz);
+			}
+		}
+		break;
+
+	case STATUSTYPE_IMA:
+		sz = 0; /*reset the result pointer*/
+
+		DMEMIT_TARGET_NAME_VERSION(ti->type);
+		DMEMIT(",nr_priority_groups=%u", m->nr_priority_groups);
+
+		pg_counter = 0;
+		list_for_each_entry(pg, &m->priority_groups, list) {
+			if (pg->bypassed)
+				state = 'D';	/* Disabled */
+			else if (pg == m->current_pg)
+				state = 'A';	/* Currently Active */
+			else
+				state = 'E';	/* Enabled */
+			DMEMIT(",pg_state_%d=%c", pg_counter, state);
+			DMEMIT(",nr_pgpaths_%d=%u", pg_counter, pg->nr_pgpaths);
+			DMEMIT(",path_selector_name_%d=%s", pg_counter, pg->ps.type->name);
+
+			pgpath_counter = 0;
+			list_for_each_entry(p, &pg->pgpaths, list) {
+				DMEMIT(",path_name_%d_%d=%s,is_active_%d_%d=%c,fail_count_%d_%d=%u",
+				       pg_counter, pgpath_counter, p->path.dev->name,
+				       pg_counter, pgpath_counter, p->is_active ? 'A' : 'F',
+				       pg_counter, pgpath_counter, p->fail_count);
+				if (pg->ps.type->status) {
+					DMEMIT(",path_selector_status_%d_%d=",
+					       pg_counter, pgpath_counter);
+					sz += pg->ps.type->status(&pg->ps, &p->path,
+								  type, result + sz,
+								  maxlen - sz);
+				}
+				pgpath_counter++;
+			}
+			pg_counter++;
+		}
+		DMEMIT(";");
+		break;
+	}
+
+	spin_unlock_irqrestore(&m->lock, flags);
+}
+
+static int multipath_message(struct dm_target *ti, unsigned int argc, char **argv,
+			     char *result, unsigned int maxlen)
+{
+	int r = -EINVAL;
+	struct dm_dev *dev;
+	struct multipath *m = ti->private;
+	action_fn action;
+	unsigned long flags;
+
+	mutex_lock(&m->work_mutex);
+
+	if (dm_suspended(ti)) {
+		r = -EBUSY;
+		goto out;
+	}
+
+	if (argc == 1) {
+		if (!strcasecmp(argv[0], "queue_if_no_path")) {
+			r = queue_if_no_path(m, true, false, __func__);
+			spin_lock_irqsave(&m->lock, flags);
+			enable_nopath_timeout(m);
+			spin_unlock_irqrestore(&m->lock, flags);
+			goto out;
+		} else if (!strcasecmp(argv[0], "fail_if_no_path")) {
+			r = queue_if_no_path(m, false, false, __func__);
+			disable_nopath_timeout(m);
+			goto out;
+		}
+	}
+
+	if (argc != 2) {
+		DMWARN("Invalid multipath message arguments. Expected 2 arguments, got %d.", argc);
+		goto out;
+	}
+
+	if (!strcasecmp(argv[0], "disable_group")) {
+		r = bypass_pg_num(m, argv[1], true);
+		goto out;
+	} else if (!strcasecmp(argv[0], "enable_group")) {
+		r = bypass_pg_num(m, argv[1], false);
+		goto out;
+	} else if (!strcasecmp(argv[0], "switch_group")) {
+		r = switch_pg_num(m, argv[1]);
+		goto out;
+	} else if (!strcasecmp(argv[0], "reinstate_path"))
+		action = reinstate_path;
+	else if (!strcasecmp(argv[0], "fail_path"))
+		action = fail_path;
+	else {
+		DMWARN("Unrecognised multipath message received: %s", argv[0]);
+		goto out;
+	}
+
+	r = dm_get_device(ti, argv[1], dm_table_get_mode(ti->table), &dev);
+	if (r) {
+		DMWARN("message: error getting device %s",
+		       argv[1]);
+		goto out;
+	}
+
+	r = action_dev(m, dev, action);
+
+	dm_put_device(ti, dev);
+
+out:
+	mutex_unlock(&m->work_mutex);
+	return r;
+}
+
+static int multipath_prepare_ioctl(struct dm_target *ti,
+				   struct block_device **bdev)
+{
+	struct multipath *m = ti->private;
+	struct pgpath *pgpath;
+	unsigned long flags;
+	int r;
+
+	pgpath = READ_ONCE(m->current_pgpath);
+	if (!pgpath || !mpath_double_check_test_bit(MPATHF_QUEUE_IO, m))
+		pgpath = choose_pgpath(m, 0);
+
+	if (pgpath) {
+		if (!mpath_double_check_test_bit(MPATHF_QUEUE_IO, m)) {
+			*bdev = pgpath->path.dev->bdev;
+			r = 0;
+		} else {
+			/* pg_init has not started or completed */
+			r = -ENOTCONN;
+		}
+	} else {
+		/* No path is available */
+		r = -EIO;
+		spin_lock_irqsave(&m->lock, flags);
+		if (test_bit(MPATHF_QUEUE_IF_NO_PATH, &m->flags))
+			r = -ENOTCONN;
+		spin_unlock_irqrestore(&m->lock, flags);
+	}
+
+	if (r == -ENOTCONN) {
+		if (!READ_ONCE(m->current_pg)) {
+			/* Path status changed, redo selection */
+			(void) choose_pgpath(m, 0);
+		}
+		spin_lock_irqsave(&m->lock, flags);
+		if (test_bit(MPATHF_PG_INIT_REQUIRED, &m->flags))
+			(void) __pg_init_all_paths(m);
+		spin_unlock_irqrestore(&m->lock, flags);
+		dm_table_run_md_queue_async(m->ti->table);
+		process_queued_io_list(m);
+	}
+
+	/*
+	 * Only pass ioctls through if the device sizes match exactly.
+	 */
+	if (!r && ti->len != bdev_nr_sectors((*bdev)))
+		return 1;
+	return r;
+}
+
+static int multipath_iterate_devices(struct dm_target *ti,
+				     iterate_devices_callout_fn fn, void *data)
+{
+	struct multipath *m = ti->private;
+	struct priority_group *pg;
+	struct pgpath *p;
+	int ret = 0;
+
+	list_for_each_entry(pg, &m->priority_groups, list) {
+		list_for_each_entry(p, &pg->pgpaths, list) {
+			ret = fn(ti, p->path.dev, ti->begin, ti->len, data);
+			if (ret)
+				goto out;
+		}
+	}
+
+out:
+	return ret;
+}
+
+static int pgpath_busy(struct pgpath *pgpath)
+{
+	struct request_queue *q = bdev_get_queue(pgpath->path.dev->bdev);
+
+	return blk_lld_busy(q);
+}
+
+/*
+ * We return "busy", only when we can map I/Os but underlying devices
+ * are busy (so even if we map I/Os now, the I/Os will wait on
+ * the underlying queue).
+ * In other words, if we want to kill I/Os or queue them inside us
+ * due to map unavailability, we don't return "busy".  Otherwise,
+ * dm core won't give us the I/Os and we can't do what we want.
+ */
+static int multipath_busy(struct dm_target *ti)
+{
+	bool busy = false, has_active = false;
+	struct multipath *m = ti->private;
+	struct priority_group *pg, *next_pg;
+	struct pgpath *pgpath;
+
+	/* pg_init in progress */
+	if (atomic_read(&m->pg_init_in_progress))
+		return true;
+
+	/* no paths available, for blk-mq: rely on IO mapping to delay requeue */
+	if (!atomic_read(&m->nr_valid_paths)) {
+		unsigned long flags;
+
+		spin_lock_irqsave(&m->lock, flags);
+		if (test_bit(MPATHF_QUEUE_IF_NO_PATH, &m->flags)) {
+			spin_unlock_irqrestore(&m->lock, flags);
+			return (m->queue_mode != DM_TYPE_REQUEST_BASED);
+		}
+		spin_unlock_irqrestore(&m->lock, flags);
+	}
+
+	/* Guess which priority_group will be used at next mapping time */
+	pg = READ_ONCE(m->current_pg);
+	next_pg = READ_ONCE(m->next_pg);
+	if (unlikely(!READ_ONCE(m->current_pgpath) && next_pg))
+		pg = next_pg;
+
+	if (!pg) {
+		/*
+		 * We don't know which pg will be used at next mapping time.
+		 * We don't call choose_pgpath() here to avoid to trigger
+		 * pg_init just by busy checking.
+		 * So we don't know whether underlying devices we will be using
+		 * at next mapping time are busy or not. Just try mapping.
+		 */
+		return busy;
+	}
+
+	/*
+	 * If there is one non-busy active path at least, the path selector
+	 * will be able to select it. So we consider such a pg as not busy.
+	 */
+	busy = true;
+	list_for_each_entry(pgpath, &pg->pgpaths, list) {
+		if (pgpath->is_active) {
+			has_active = true;
+			if (!pgpath_busy(pgpath)) {
+				busy = false;
+				break;
+			}
+		}
+	}
+
+	if (!has_active) {
+		/*
+		 * No active path in this pg, so this pg won't be used and
+		 * the current_pg will be changed at next mapping time.
+		 * We need to try mapping to determine it.
+		 */
+		busy = false;
+	}
+
+	return busy;
+}
+
+/*
+ *---------------------------------------------------------------
+ * Module setup
+ *---------------------------------------------------------------
+ */
+static struct target_type multipath_target = {
+	.name = "multipath",
+	.version = {1, 14, 0},
+	.features = DM_TARGET_SINGLETON | DM_TARGET_IMMUTABLE |
+		    DM_TARGET_PASSES_INTEGRITY,
+	.module = THIS_MODULE,
+	.ctr = multipath_ctr,
+	.dtr = multipath_dtr,
+	.clone_and_map_rq = multipath_clone_and_map,
+	.release_clone_rq = multipath_release_clone,
+	.rq_end_io = multipath_end_io,
+	.map = multipath_map_bio,
+	.end_io = multipath_end_io_bio,
+	.presuspend = multipath_presuspend,
+	.postsuspend = multipath_postsuspend,
+	.resume = multipath_resume,
+	.status = multipath_status,
+	.message = multipath_message,
+	.prepare_ioctl = multipath_prepare_ioctl,
+	.iterate_devices = multipath_iterate_devices,
+	.busy = multipath_busy,
+};
+
+static int __init dm_multipath_init(void)
+{
+	int r = -ENOMEM;
+
+	kmultipathd = alloc_workqueue("kmpathd", WQ_MEM_RECLAIM, 0);
+	if (!kmultipathd) {
+		DMERR("failed to create workqueue kmpathd");
+		goto bad_alloc_kmultipathd;
+	}
+
+	/*
+	 * A separate workqueue is used to handle the device handlers
+	 * to avoid overloading existing workqueue. Overloading the
+	 * old workqueue would also create a bottleneck in the
+	 * path of the storage hardware device activation.
+	 */
+	kmpath_handlerd = alloc_ordered_workqueue("kmpath_handlerd",
+						  WQ_MEM_RECLAIM);
+	if (!kmpath_handlerd) {
+		DMERR("failed to create workqueue kmpath_handlerd");
+		goto bad_alloc_kmpath_handlerd;
+	}
+
+	dm_mpath_wq = alloc_workqueue("dm_mpath_wq", 0, 0);
+	if (!dm_mpath_wq) {
+		DMERR("failed to create workqueue dm_mpath_wq");
+		goto bad_alloc_dm_mpath_wq;
+	}
+
+	r = dm_register_target(&multipath_target);
+	if (r < 0)
+		goto bad_register_target;
+
+	return 0;
+
+bad_register_target:
+	destroy_workqueue(dm_mpath_wq);
+bad_alloc_dm_mpath_wq:
+	destroy_workqueue(kmpath_handlerd);
+bad_alloc_kmpath_handlerd:
+	destroy_workqueue(kmultipathd);
+bad_alloc_kmultipathd:
+	return r;
+}
+
+static void __exit dm_multipath_exit(void)
+{
+	destroy_workqueue(dm_mpath_wq);
+	destroy_workqueue(kmpath_handlerd);
+	destroy_workqueue(kmultipathd);
+
+	dm_unregister_target(&multipath_target);
+}
+
+module_init(dm_multipath_init);
+module_exit(dm_multipath_exit);
+
+module_param_named(queue_if_no_path_timeout_secs, queue_if_no_path_timeout_secs, ulong, 0644);
+MODULE_PARM_DESC(queue_if_no_path_timeout_secs, "No available paths queue IO timeout in seconds");
+
+MODULE_DESCRIPTION(DM_NAME " multipath target");
+MODULE_AUTHOR("Sistina Software <dm-devel@redhat.com>");
+MODULE_LICENSE("GPL");