Adding upstream version 4.19.249.upstream/4.19.249

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

1 files changed, 3978 insertions, 0 deletions

diff --git a/block/blk-core.c b/block/blk-core.c
new file mode 100644
index 000000000..80f3e729f
--- /dev/null
+++ b/block/blk-core.c
@@ -0,0 +1,3978 @@
+/*
+ * Copyright (C) 1991, 1992 Linus Torvalds
+ * Copyright (C) 1994,      Karl Keyte: Added support for disk statistics
+ * Elevator latency, (C) 2000  Andrea Arcangeli <andrea@suse.de> SuSE
+ * Queue request tables / lock, selectable elevator, Jens Axboe <axboe@suse.de>
+ * kernel-doc documentation started by NeilBrown <neilb@cse.unsw.edu.au>
+ *	-  July2000
+ * bio rewrite, highmem i/o, etc, Jens Axboe <axboe@suse.de> - may 2001
+ */
+
+/*
+ * This handles all read/write requests to block devices
+ */
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/backing-dev.h>
+#include <linux/bio.h>
+#include <linux/blkdev.h>
+#include <linux/blk-mq.h>
+#include <linux/highmem.h>
+#include <linux/mm.h>
+#include <linux/kernel_stat.h>
+#include <linux/string.h>
+#include <linux/init.h>
+#include <linux/completion.h>
+#include <linux/slab.h>
+#include <linux/swap.h>
+#include <linux/writeback.h>
+#include <linux/task_io_accounting_ops.h>
+#include <linux/fault-inject.h>
+#include <linux/list_sort.h>
+#include <linux/delay.h>
+#include <linux/ratelimit.h>
+#include <linux/pm_runtime.h>
+#include <linux/blk-cgroup.h>
+#include <linux/debugfs.h>
+#include <linux/bpf.h>
+
+#define CREATE_TRACE_POINTS
+#include <trace/events/block.h>
+
+#include "blk.h"
+#include "blk-mq.h"
+#include "blk-mq-sched.h"
+#include "blk-rq-qos.h"
+
+#ifdef CONFIG_DEBUG_FS
+struct dentry *blk_debugfs_root;
+#endif
+
+EXPORT_TRACEPOINT_SYMBOL_GPL(block_bio_remap);
+EXPORT_TRACEPOINT_SYMBOL_GPL(block_rq_remap);
+EXPORT_TRACEPOINT_SYMBOL_GPL(block_bio_complete);
+EXPORT_TRACEPOINT_SYMBOL_GPL(block_split);
+EXPORT_TRACEPOINT_SYMBOL_GPL(block_unplug);
+
+DEFINE_IDA(blk_queue_ida);
+
+/*
+ * For the allocated request tables
+ */
+struct kmem_cache *request_cachep;
+
+/*
+ * For queue allocation
+ */
+struct kmem_cache *blk_requestq_cachep;
+
+/*
+ * Controlling structure to kblockd
+ */
+static struct workqueue_struct *kblockd_workqueue;
+
+/**
+ * blk_queue_flag_set - atomically set a queue flag
+ * @flag: flag to be set
+ * @q: request queue
+ */
+void blk_queue_flag_set(unsigned int flag, struct request_queue *q)
+{
+	unsigned long flags;
+
+	spin_lock_irqsave(q->queue_lock, flags);
+	queue_flag_set(flag, q);
+	spin_unlock_irqrestore(q->queue_lock, flags);
+}
+EXPORT_SYMBOL(blk_queue_flag_set);
+
+/**
+ * blk_queue_flag_clear - atomically clear a queue flag
+ * @flag: flag to be cleared
+ * @q: request queue
+ */
+void blk_queue_flag_clear(unsigned int flag, struct request_queue *q)
+{
+	unsigned long flags;
+
+	spin_lock_irqsave(q->queue_lock, flags);
+	queue_flag_clear(flag, q);
+	spin_unlock_irqrestore(q->queue_lock, flags);
+}
+EXPORT_SYMBOL(blk_queue_flag_clear);
+
+/**
+ * blk_queue_flag_test_and_set - atomically test and set a queue flag
+ * @flag: flag to be set
+ * @q: request queue
+ *
+ * Returns the previous value of @flag - 0 if the flag was not set and 1 if
+ * the flag was already set.
+ */
+bool blk_queue_flag_test_and_set(unsigned int flag, struct request_queue *q)
+{
+	unsigned long flags;
+	bool res;
+
+	spin_lock_irqsave(q->queue_lock, flags);
+	res = queue_flag_test_and_set(flag, q);
+	spin_unlock_irqrestore(q->queue_lock, flags);
+
+	return res;
+}
+EXPORT_SYMBOL_GPL(blk_queue_flag_test_and_set);
+
+/**
+ * blk_queue_flag_test_and_clear - atomically test and clear a queue flag
+ * @flag: flag to be cleared
+ * @q: request queue
+ *
+ * Returns the previous value of @flag - 0 if the flag was not set and 1 if
+ * the flag was set.
+ */
+bool blk_queue_flag_test_and_clear(unsigned int flag, struct request_queue *q)
+{
+	unsigned long flags;
+	bool res;
+
+	spin_lock_irqsave(q->queue_lock, flags);
+	res = queue_flag_test_and_clear(flag, q);
+	spin_unlock_irqrestore(q->queue_lock, flags);
+
+	return res;
+}
+EXPORT_SYMBOL_GPL(blk_queue_flag_test_and_clear);
+
+static void blk_clear_congested(struct request_list *rl, int sync)
+{
+#ifdef CONFIG_CGROUP_WRITEBACK
+	clear_wb_congested(rl->blkg->wb_congested, sync);
+#else
+	/*
+	 * If !CGROUP_WRITEBACK, all blkg's map to bdi->wb and we shouldn't
+	 * flip its congestion state for events on other blkcgs.
+	 */
+	if (rl == &rl->q->root_rl)
+		clear_wb_congested(rl->q->backing_dev_info->wb.congested, sync);
+#endif
+}
+
+static void blk_set_congested(struct request_list *rl, int sync)
+{
+#ifdef CONFIG_CGROUP_WRITEBACK
+	set_wb_congested(rl->blkg->wb_congested, sync);
+#else
+	/* see blk_clear_congested() */
+	if (rl == &rl->q->root_rl)
+		set_wb_congested(rl->q->backing_dev_info->wb.congested, sync);
+#endif
+}
+
+void blk_queue_congestion_threshold(struct request_queue *q)
+{
+	int nr;
+
+	nr = q->nr_requests - (q->nr_requests / 8) + 1;
+	if (nr > q->nr_requests)
+		nr = q->nr_requests;
+	q->nr_congestion_on = nr;
+
+	nr = q->nr_requests - (q->nr_requests / 8) - (q->nr_requests / 16) - 1;
+	if (nr < 1)
+		nr = 1;
+	q->nr_congestion_off = nr;
+}
+
+void blk_rq_init(struct request_queue *q, struct request *rq)
+{
+	memset(rq, 0, sizeof(*rq));
+
+	INIT_LIST_HEAD(&rq->queuelist);
+	INIT_LIST_HEAD(&rq->timeout_list);
+	rq->cpu = -1;
+	rq->q = q;
+	rq->__sector = (sector_t) -1;
+	INIT_HLIST_NODE(&rq->hash);
+	RB_CLEAR_NODE(&rq->rb_node);
+	rq->tag = -1;
+	rq->internal_tag = -1;
+	rq->start_time_ns = ktime_get_ns();
+	rq->part = NULL;
+	refcount_set(&rq->ref, 1);
+}
+EXPORT_SYMBOL(blk_rq_init);
+
+static const struct {
+	int		errno;
+	const char	*name;
+} blk_errors[] = {
+	[BLK_STS_OK]		= { 0,		"" },
+	[BLK_STS_NOTSUPP]	= { -EOPNOTSUPP, "operation not supported" },
+	[BLK_STS_TIMEOUT]	= { -ETIMEDOUT,	"timeout" },
+	[BLK_STS_NOSPC]		= { -ENOSPC,	"critical space allocation" },
+	[BLK_STS_TRANSPORT]	= { -ENOLINK,	"recoverable transport" },
+	[BLK_STS_TARGET]	= { -EREMOTEIO,	"critical target" },
+	[BLK_STS_NEXUS]		= { -EBADE,	"critical nexus" },
+	[BLK_STS_MEDIUM]	= { -ENODATA,	"critical medium" },
+	[BLK_STS_PROTECTION]	= { -EILSEQ,	"protection" },
+	[BLK_STS_RESOURCE]	= { -ENOMEM,	"kernel resource" },
+	[BLK_STS_DEV_RESOURCE]	= { -EBUSY,	"device resource" },
+	[BLK_STS_AGAIN]		= { -EAGAIN,	"nonblocking retry" },
+
+	/* device mapper special case, should not leak out: */
+	[BLK_STS_DM_REQUEUE]	= { -EREMCHG, "dm internal retry" },
+
+	/* everything else not covered above: */
+	[BLK_STS_IOERR]		= { -EIO,	"I/O" },
+};
+
+blk_status_t errno_to_blk_status(int errno)
+{
+	int i;
+
+	for (i = 0; i < ARRAY_SIZE(blk_errors); i++) {
+		if (blk_errors[i].errno == errno)
+			return (__force blk_status_t)i;
+	}
+
+	return BLK_STS_IOERR;
+}
+EXPORT_SYMBOL_GPL(errno_to_blk_status);
+
+int blk_status_to_errno(blk_status_t status)
+{
+	int idx = (__force int)status;
+
+	if (WARN_ON_ONCE(idx >= ARRAY_SIZE(blk_errors)))
+		return -EIO;
+	return blk_errors[idx].errno;
+}
+EXPORT_SYMBOL_GPL(blk_status_to_errno);
+
+static void print_req_error(struct request *req, blk_status_t status)
+{
+	int idx = (__force int)status;
+
+	if (WARN_ON_ONCE(idx >= ARRAY_SIZE(blk_errors)))
+		return;
+
+	printk_ratelimited(KERN_ERR "%s: %s error, dev %s, sector %llu\n",
+			   __func__, blk_errors[idx].name, req->rq_disk ?
+			   req->rq_disk->disk_name : "?",
+			   (unsigned long long)blk_rq_pos(req));
+}
+
+static void req_bio_endio(struct request *rq, struct bio *bio,
+			  unsigned int nbytes, blk_status_t error)
+{
+	if (error)
+		bio->bi_status = error;
+
+	if (unlikely(rq->rq_flags & RQF_QUIET))
+		bio_set_flag(bio, BIO_QUIET);
+
+	bio_advance(bio, nbytes);
+
+	/* don't actually finish bio if it's part of flush sequence */
+	if (bio->bi_iter.bi_size == 0 && !(rq->rq_flags & RQF_FLUSH_SEQ))
+		bio_endio(bio);
+}
+
+void blk_dump_rq_flags(struct request *rq, char *msg)
+{
+	printk(KERN_INFO "%s: dev %s: flags=%llx\n", msg,
+		rq->rq_disk ? rq->rq_disk->disk_name : "?",
+		(unsigned long long) rq->cmd_flags);
+
+	printk(KERN_INFO "  sector %llu, nr/cnr %u/%u\n",
+	       (unsigned long long)blk_rq_pos(rq),
+	       blk_rq_sectors(rq), blk_rq_cur_sectors(rq));
+	printk(KERN_INFO "  bio %p, biotail %p, len %u\n",
+	       rq->bio, rq->biotail, blk_rq_bytes(rq));
+}
+EXPORT_SYMBOL(blk_dump_rq_flags);
+
+static void blk_delay_work(struct work_struct *work)
+{
+	struct request_queue *q;
+
+	q = container_of(work, struct request_queue, delay_work.work);
+	spin_lock_irq(q->queue_lock);
+	__blk_run_queue(q);
+	spin_unlock_irq(q->queue_lock);
+}
+
+/**
+ * blk_delay_queue - restart queueing after defined interval
+ * @q:		The &struct request_queue in question
+ * @msecs:	Delay in msecs
+ *
+ * Description:
+ *   Sometimes queueing needs to be postponed for a little while, to allow
+ *   resources to come back. This function will make sure that queueing is
+ *   restarted around the specified time.
+ */
+void blk_delay_queue(struct request_queue *q, unsigned long msecs)
+{
+	lockdep_assert_held(q->queue_lock);
+	WARN_ON_ONCE(q->mq_ops);
+
+	if (likely(!blk_queue_dead(q)))
+		queue_delayed_work(kblockd_workqueue, &q->delay_work,
+				   msecs_to_jiffies(msecs));
+}
+EXPORT_SYMBOL(blk_delay_queue);
+
+/**
+ * blk_start_queue_async - asynchronously restart a previously stopped queue
+ * @q:    The &struct request_queue in question
+ *
+ * Description:
+ *   blk_start_queue_async() will clear the stop flag on the queue, and
+ *   ensure that the request_fn for the queue is run from an async
+ *   context.
+ **/
+void blk_start_queue_async(struct request_queue *q)
+{
+	lockdep_assert_held(q->queue_lock);
+	WARN_ON_ONCE(q->mq_ops);
+
+	queue_flag_clear(QUEUE_FLAG_STOPPED, q);
+	blk_run_queue_async(q);
+}
+EXPORT_SYMBOL(blk_start_queue_async);
+
+/**
+ * blk_start_queue - restart a previously stopped queue
+ * @q:    The &struct request_queue in question
+ *
+ * Description:
+ *   blk_start_queue() will clear the stop flag on the queue, and call
+ *   the request_fn for the queue if it was in a stopped state when
+ *   entered. Also see blk_stop_queue().
+ **/
+void blk_start_queue(struct request_queue *q)
+{
+	lockdep_assert_held(q->queue_lock);
+	WARN_ON_ONCE(q->mq_ops);
+
+	queue_flag_clear(QUEUE_FLAG_STOPPED, q);
+	__blk_run_queue(q);
+}
+EXPORT_SYMBOL(blk_start_queue);
+
+/**
+ * blk_stop_queue - stop a queue
+ * @q:    The &struct request_queue in question
+ *
+ * Description:
+ *   The Linux block layer assumes that a block driver will consume all
+ *   entries on the request queue when the request_fn strategy is called.
+ *   Often this will not happen, because of hardware limitations (queue
+ *   depth settings). If a device driver gets a 'queue full' response,
+ *   or if it simply chooses not to queue more I/O at one point, it can
+ *   call this function to prevent the request_fn from being called until
+ *   the driver has signalled it's ready to go again. This happens by calling
+ *   blk_start_queue() to restart queue operations.
+ **/
+void blk_stop_queue(struct request_queue *q)
+{
+	lockdep_assert_held(q->queue_lock);
+	WARN_ON_ONCE(q->mq_ops);
+
+	cancel_delayed_work(&q->delay_work);
+	queue_flag_set(QUEUE_FLAG_STOPPED, q);
+}
+EXPORT_SYMBOL(blk_stop_queue);
+
+/**
+ * blk_sync_queue - cancel any pending callbacks on a queue
+ * @q: the queue
+ *
+ * Description:
+ *     The block layer may perform asynchronous callback activity
+ *     on a queue, such as calling the unplug function after a timeout.
+ *     A block device may call blk_sync_queue to ensure that any
+ *     such activity is cancelled, thus allowing it to release resources
+ *     that the callbacks might use. The caller must already have made sure
+ *     that its ->make_request_fn will not re-add plugging prior to calling
+ *     this function.
+ *
+ *     This function does not cancel any asynchronous activity arising
+ *     out of elevator or throttling code. That would require elevator_exit()
+ *     and blkcg_exit_queue() to be called with queue lock initialized.
+ *
+ */
+void blk_sync_queue(struct request_queue *q)
+{
+	del_timer_sync(&q->timeout);
+	cancel_work_sync(&q->timeout_work);
+
+	if (q->mq_ops) {
+		struct blk_mq_hw_ctx *hctx;
+		int i;
+
+		queue_for_each_hw_ctx(q, hctx, i)
+			cancel_delayed_work_sync(&hctx->run_work);
+	} else {
+		cancel_delayed_work_sync(&q->delay_work);
+	}
+}
+EXPORT_SYMBOL(blk_sync_queue);
+
+/**
+ * blk_set_pm_only - increment pm_only counter
+ * @q: request queue pointer
+ */
+void blk_set_pm_only(struct request_queue *q)
+{
+	atomic_inc(&q->pm_only);
+}
+EXPORT_SYMBOL_GPL(blk_set_pm_only);
+
+void blk_clear_pm_only(struct request_queue *q)
+{
+	int pm_only;
+
+	pm_only = atomic_dec_return(&q->pm_only);
+	WARN_ON_ONCE(pm_only < 0);
+	if (pm_only == 0)
+		wake_up_all(&q->mq_freeze_wq);
+}
+EXPORT_SYMBOL_GPL(blk_clear_pm_only);
+
+/**
+ * __blk_run_queue_uncond - run a queue whether or not it has been stopped
+ * @q:	The queue to run
+ *
+ * Description:
+ *    Invoke request handling on a queue if there are any pending requests.
+ *    May be used to restart request handling after a request has completed.
+ *    This variant runs the queue whether or not the queue has been
+ *    stopped. Must be called with the queue lock held and interrupts
+ *    disabled. See also @blk_run_queue.
+ */
+inline void __blk_run_queue_uncond(struct request_queue *q)
+{
+	lockdep_assert_held(q->queue_lock);
+	WARN_ON_ONCE(q->mq_ops);
+
+	if (unlikely(blk_queue_dead(q)))
+		return;
+
+	/*
+	 * Some request_fn implementations, e.g. scsi_request_fn(), unlock
+	 * the queue lock internally. As a result multiple threads may be
+	 * running such a request function concurrently. Keep track of the
+	 * number of active request_fn invocations such that blk_drain_queue()
+	 * can wait until all these request_fn calls have finished.
+	 */
+	q->request_fn_active++;
+	q->request_fn(q);
+	q->request_fn_active--;
+}
+EXPORT_SYMBOL_GPL(__blk_run_queue_uncond);
+
+/**
+ * __blk_run_queue - run a single device queue
+ * @q:	The queue to run
+ *
+ * Description:
+ *    See @blk_run_queue.
+ */
+void __blk_run_queue(struct request_queue *q)
+{
+	lockdep_assert_held(q->queue_lock);
+	WARN_ON_ONCE(q->mq_ops);
+
+	if (unlikely(blk_queue_stopped(q)))
+		return;
+
+	__blk_run_queue_uncond(q);
+}
+EXPORT_SYMBOL(__blk_run_queue);
+
+/**
+ * blk_run_queue_async - run a single device queue in workqueue context
+ * @q:	The queue to run
+ *
+ * Description:
+ *    Tells kblockd to perform the equivalent of @blk_run_queue on behalf
+ *    of us.
+ *
+ * Note:
+ *    Since it is not allowed to run q->delay_work after blk_cleanup_queue()
+ *    has canceled q->delay_work, callers must hold the queue lock to avoid
+ *    race conditions between blk_cleanup_queue() and blk_run_queue_async().
+ */
+void blk_run_queue_async(struct request_queue *q)
+{
+	lockdep_assert_held(q->queue_lock);
+	WARN_ON_ONCE(q->mq_ops);
+
+	if (likely(!blk_queue_stopped(q) && !blk_queue_dead(q)))
+		mod_delayed_work(kblockd_workqueue, &q->delay_work, 0);
+}
+EXPORT_SYMBOL(blk_run_queue_async);
+
+/**
+ * blk_run_queue - run a single device queue
+ * @q: The queue to run
+ *
+ * Description:
+ *    Invoke request handling on this queue, if it has pending work to do.
+ *    May be used to restart queueing when a request has completed.
+ */
+void blk_run_queue(struct request_queue *q)
+{
+	unsigned long flags;
+
+	WARN_ON_ONCE(q->mq_ops);
+
+	spin_lock_irqsave(q->queue_lock, flags);
+	__blk_run_queue(q);
+	spin_unlock_irqrestore(q->queue_lock, flags);
+}
+EXPORT_SYMBOL(blk_run_queue);
+
+void blk_put_queue(struct request_queue *q)
+{
+	kobject_put(&q->kobj);
+}
+EXPORT_SYMBOL(blk_put_queue);
+
+/**
+ * __blk_drain_queue - drain requests from request_queue
+ * @q: queue to drain
+ * @drain_all: whether to drain all requests or only the ones w/ ELVPRIV
+ *
+ * Drain requests from @q.  If @drain_all is set, all requests are drained.
+ * If not, only ELVPRIV requests are drained.  The caller is responsible
+ * for ensuring that no new requests which need to be drained are queued.
+ */
+static void __blk_drain_queue(struct request_queue *q, bool drain_all)
+	__releases(q->queue_lock)
+	__acquires(q->queue_lock)
+{
+	int i;
+
+	lockdep_assert_held(q->queue_lock);
+	WARN_ON_ONCE(q->mq_ops);
+
+	while (true) {
+		bool drain = false;
+
+		/*
+		 * The caller might be trying to drain @q before its
+		 * elevator is initialized.
+		 */
+		if (q->elevator)
+			elv_drain_elevator(q);
+
+		blkcg_drain_queue(q);
+
+		/*
+		 * This function might be called on a queue which failed
+		 * driver init after queue creation or is not yet fully
+		 * active yet.  Some drivers (e.g. fd and loop) get unhappy
+		 * in such cases.  Kick queue iff dispatch queue has
+		 * something on it and @q has request_fn set.
+		 */
+		if (!list_empty(&q->queue_head) && q->request_fn)
+			__blk_run_queue(q);
+
+		drain |= q->nr_rqs_elvpriv;
+		drain |= q->request_fn_active;
+
+		/*
+		 * Unfortunately, requests are queued at and tracked from
+		 * multiple places and there's no single counter which can
+		 * be drained.  Check all the queues and counters.
+		 */
+		if (drain_all) {
+			struct blk_flush_queue *fq = blk_get_flush_queue(q, NULL);
+			drain |= !list_empty(&q->queue_head);
+			for (i = 0; i < 2; i++) {
+				drain |= q->nr_rqs[i];
+				drain |= q->in_flight[i];
+				if (fq)
+				    drain |= !list_empty(&fq->flush_queue[i]);
+			}
+		}
+
+		if (!drain)
+			break;
+
+		spin_unlock_irq(q->queue_lock);
+
+		msleep(10);
+
+		spin_lock_irq(q->queue_lock);
+	}
+
+	/*
+	 * With queue marked dead, any woken up waiter will fail the
+	 * allocation path, so the wakeup chaining is lost and we're
+	 * left with hung waiters. We need to wake up those waiters.
+	 */
+	if (q->request_fn) {
+		struct request_list *rl;
+
+		blk_queue_for_each_rl(rl, q)
+			for (i = 0; i < ARRAY_SIZE(rl->wait); i++)
+				wake_up_all(&rl->wait[i]);
+	}
+}
+
+void blk_drain_queue(struct request_queue *q)
+{
+	spin_lock_irq(q->queue_lock);
+	__blk_drain_queue(q, true);
+	spin_unlock_irq(q->queue_lock);
+}
+
+/**
+ * blk_queue_bypass_start - enter queue bypass mode
+ * @q: queue of interest
+ *
+ * In bypass mode, only the dispatch FIFO queue of @q is used.  This
+ * function makes @q enter bypass mode and drains all requests which were
+ * throttled or issued before.  On return, it's guaranteed that no request
+ * is being throttled or has ELVPRIV set and blk_queue_bypass() %true
+ * inside queue or RCU read lock.
+ */
+void blk_queue_bypass_start(struct request_queue *q)
+{
+	WARN_ON_ONCE(q->mq_ops);
+
+	spin_lock_irq(q->queue_lock);
+	q->bypass_depth++;
+	queue_flag_set(QUEUE_FLAG_BYPASS, q);
+	spin_unlock_irq(q->queue_lock);
+
+	/*
+	 * Queues start drained.  Skip actual draining till init is
+	 * complete.  This avoids lenghty delays during queue init which
+	 * can happen many times during boot.
+	 */
+	if (blk_queue_init_done(q)) {
+		spin_lock_irq(q->queue_lock);
+		__blk_drain_queue(q, false);
+		spin_unlock_irq(q->queue_lock);
+
+		/* ensure blk_queue_bypass() is %true inside RCU read lock */
+		synchronize_rcu();
+	}
+}
+EXPORT_SYMBOL_GPL(blk_queue_bypass_start);
+
+/**
+ * blk_queue_bypass_end - leave queue bypass mode
+ * @q: queue of interest
+ *
+ * Leave bypass mode and restore the normal queueing behavior.
+ *
+ * Note: although blk_queue_bypass_start() is only called for blk-sq queues,
+ * this function is called for both blk-sq and blk-mq queues.
+ */
+void blk_queue_bypass_end(struct request_queue *q)
+{
+	spin_lock_irq(q->queue_lock);
+	if (!--q->bypass_depth)
+		queue_flag_clear(QUEUE_FLAG_BYPASS, q);
+	WARN_ON_ONCE(q->bypass_depth < 0);
+	spin_unlock_irq(q->queue_lock);
+}
+EXPORT_SYMBOL_GPL(blk_queue_bypass_end);
+
+void blk_set_queue_dying(struct request_queue *q)
+{
+	blk_queue_flag_set(QUEUE_FLAG_DYING, q);
+
+	/*
+	 * When queue DYING flag is set, we need to block new req
+	 * entering queue, so we call blk_freeze_queue_start() to
+	 * prevent I/O from crossing blk_queue_enter().
+	 */
+	blk_freeze_queue_start(q);
+
+	if (q->mq_ops)
+		blk_mq_wake_waiters(q);
+	else {
+		struct request_list *rl;
+
+		spin_lock_irq(q->queue_lock);
+		blk_queue_for_each_rl(rl, q) {
+			if (rl->rq_pool) {
+				wake_up_all(&rl->wait[BLK_RW_SYNC]);
+				wake_up_all(&rl->wait[BLK_RW_ASYNC]);
+			}
+		}
+		spin_unlock_irq(q->queue_lock);
+	}
+
+	/* Make blk_queue_enter() reexamine the DYING flag. */
+	wake_up_all(&q->mq_freeze_wq);
+}
+EXPORT_SYMBOL_GPL(blk_set_queue_dying);
+
+/* Unconfigure the I/O scheduler and dissociate from the cgroup controller. */
+void blk_exit_queue(struct request_queue *q)
+{
+	/*
+	 * Since the I/O scheduler exit code may access cgroup information,
+	 * perform I/O scheduler exit before disassociating from the block
+	 * cgroup controller.
+	 */
+	if (q->elevator) {
+		ioc_clear_queue(q);
+		elevator_exit(q, q->elevator);
+		q->elevator = NULL;
+	}
+
+	/*
+	 * Remove all references to @q from the block cgroup controller before
+	 * restoring @q->queue_lock to avoid that restoring this pointer causes
+	 * e.g. blkcg_print_blkgs() to crash.
+	 */
+	blkcg_exit_queue(q);
+
+	/*
+	 * Since the cgroup code may dereference the @q->backing_dev_info
+	 * pointer, only decrease its reference count after having removed the
+	 * association with the block cgroup controller.
+	 */
+	bdi_put(q->backing_dev_info);
+}
+
+/**
+ * blk_cleanup_queue - shutdown a request queue
+ * @q: request queue to shutdown
+ *
+ * Mark @q DYING, drain all pending requests, mark @q DEAD, destroy and
+ * put it.  All future requests will be failed immediately with -ENODEV.
+ */
+void blk_cleanup_queue(struct request_queue *q)
+{
+	spinlock_t *lock = q->queue_lock;
+
+	/* mark @q DYING, no new request or merges will be allowed afterwards */
+	mutex_lock(&q->sysfs_lock);
+	blk_set_queue_dying(q);
+	spin_lock_irq(lock);
+
+	/*
+	 * A dying queue is permanently in bypass mode till released.  Note
+	 * that, unlike blk_queue_bypass_start(), we aren't performing
+	 * synchronize_rcu() after entering bypass mode to avoid the delay
+	 * as some drivers create and destroy a lot of queues while
+	 * probing.  This is still safe because blk_release_queue() will be
+	 * called only after the queue refcnt drops to zero and nothing,
+	 * RCU or not, would be traversing the queue by then.
+	 */
+	q->bypass_depth++;
+	queue_flag_set(QUEUE_FLAG_BYPASS, q);
+
+	queue_flag_set(QUEUE_FLAG_NOMERGES, q);
+	queue_flag_set(QUEUE_FLAG_NOXMERGES, q);
+	queue_flag_set(QUEUE_FLAG_DYING, q);
+	spin_unlock_irq(lock);
+	mutex_unlock(&q->sysfs_lock);
+
+	/*
+	 * Drain all requests queued before DYING marking. Set DEAD flag to
+	 * prevent that q->request_fn() gets invoked after draining finished.
+	 */
+	blk_freeze_queue(q);
+
+	rq_qos_exit(q);
+
+	spin_lock_irq(lock);
+	queue_flag_set(QUEUE_FLAG_DEAD, q);
+	spin_unlock_irq(lock);
+
+	/*
+	 * make sure all in-progress dispatch are completed because
+	 * blk_freeze_queue() can only complete all requests, and
+	 * dispatch may still be in-progress since we dispatch requests
+	 * from more than one contexts.
+	 *
+	 * We rely on driver to deal with the race in case that queue
+	 * initialization isn't done.
+	 */
+	if (q->mq_ops && blk_queue_init_done(q))
+		blk_mq_quiesce_queue(q);
+
+	/* for synchronous bio-based driver finish in-flight integrity i/o */
+	blk_flush_integrity();
+
+	/* @q won't process any more request, flush async actions */
+	del_timer_sync(&q->backing_dev_info->laptop_mode_wb_timer);
+	blk_sync_queue(q);
+
+	/*
+	 * I/O scheduler exit is only safe after the sysfs scheduler attribute
+	 * has been removed.
+	 */
+	WARN_ON_ONCE(q->kobj.state_in_sysfs);
+
+	blk_exit_queue(q);
+
+	if (q->mq_ops)
+		blk_mq_exit_queue(q);
+
+	percpu_ref_exit(&q->q_usage_counter);
+
+	spin_lock_irq(lock);
+	if (q->queue_lock != &q->__queue_lock)
+		q->queue_lock = &q->__queue_lock;
+	spin_unlock_irq(lock);
+
+	/* @q is and will stay empty, shutdown and put */
+	blk_put_queue(q);
+}
+EXPORT_SYMBOL(blk_cleanup_queue);
+
+/* Allocate memory local to the request queue */
+static void *alloc_request_simple(gfp_t gfp_mask, void *data)
+{
+	struct request_queue *q = data;
+
+	return kmem_cache_alloc_node(request_cachep, gfp_mask, q->node);
+}
+
+static void free_request_simple(void *element, void *data)
+{
+	kmem_cache_free(request_cachep, element);
+}
+
+static void *alloc_request_size(gfp_t gfp_mask, void *data)
+{
+	struct request_queue *q = data;
+	struct request *rq;
+
+	rq = kmalloc_node(sizeof(struct request) + q->cmd_size, gfp_mask,
+			q->node);
+	if (rq && q->init_rq_fn && q->init_rq_fn(q, rq, gfp_mask) < 0) {
+		kfree(rq);
+		rq = NULL;
+	}
+	return rq;
+}
+
+static void free_request_size(void *element, void *data)
+{
+	struct request_queue *q = data;
+
+	if (q->exit_rq_fn)
+		q->exit_rq_fn(q, element);
+	kfree(element);
+}
+
+int blk_init_rl(struct request_list *rl, struct request_queue *q,
+		gfp_t gfp_mask)
+{
+	if (unlikely(rl->rq_pool) || q->mq_ops)
+		return 0;
+
+	rl->q = q;
+	rl->count[BLK_RW_SYNC] = rl->count[BLK_RW_ASYNC] = 0;
+	rl->starved[BLK_RW_SYNC] = rl->starved[BLK_RW_ASYNC] = 0;
+	init_waitqueue_head(&rl->wait[BLK_RW_SYNC]);
+	init_waitqueue_head(&rl->wait[BLK_RW_ASYNC]);
+
+	if (q->cmd_size) {
+		rl->rq_pool = mempool_create_node(BLKDEV_MIN_RQ,
+				alloc_request_size, free_request_size,
+				q, gfp_mask, q->node);
+	} else {
+		rl->rq_pool = mempool_create_node(BLKDEV_MIN_RQ,
+				alloc_request_simple, free_request_simple,
+				q, gfp_mask, q->node);
+	}
+	if (!rl->rq_pool)
+		return -ENOMEM;
+
+	if (rl != &q->root_rl)
+		WARN_ON_ONCE(!blk_get_queue(q));
+
+	return 0;
+}
+
+void blk_exit_rl(struct request_queue *q, struct request_list *rl)
+{
+	if (rl->rq_pool) {
+		mempool_destroy(rl->rq_pool);
+		if (rl != &q->root_rl)
+			blk_put_queue(q);
+	}
+}
+
+struct request_queue *blk_alloc_queue(gfp_t gfp_mask)
+{
+	return blk_alloc_queue_node(gfp_mask, NUMA_NO_NODE, NULL);
+}
+EXPORT_SYMBOL(blk_alloc_queue);
+
+/**
+ * blk_queue_enter() - try to increase q->q_usage_counter
+ * @q: request queue pointer
+ * @flags: BLK_MQ_REQ_NOWAIT and/or BLK_MQ_REQ_PREEMPT
+ */
+int blk_queue_enter(struct request_queue *q, blk_mq_req_flags_t flags)
+{
+	const bool pm = flags & BLK_MQ_REQ_PREEMPT;
+
+	while (true) {
+		bool success = false;
+
+		rcu_read_lock();
+		if (percpu_ref_tryget_live(&q->q_usage_counter)) {
+			/*
+			 * The code that increments the pm_only counter is
+			 * responsible for ensuring that that counter is
+			 * globally visible before the queue is unfrozen.
+			 */
+			if (pm || !blk_queue_pm_only(q)) {
+				success = true;
+			} else {
+				percpu_ref_put(&q->q_usage_counter);
+			}
+		}
+		rcu_read_unlock();
+
+		if (success)
+			return 0;
+
+		if (flags & BLK_MQ_REQ_NOWAIT)
+			return -EBUSY;
+
+		/*
+		 * read pair of barrier in blk_freeze_queue_start(),
+		 * we need to order reading __PERCPU_REF_DEAD flag of
+		 * .q_usage_counter and reading .mq_freeze_depth or
+		 * queue dying flag, otherwise the following wait may
+		 * never return if the two reads are reordered.
+		 */
+		smp_rmb();
+
+		wait_event(q->mq_freeze_wq,
+			   (atomic_read(&q->mq_freeze_depth) == 0 &&
+			    (pm || !blk_queue_pm_only(q))) ||
+			   blk_queue_dying(q));
+		if (blk_queue_dying(q))
+			return -ENODEV;
+	}
+}
+
+void blk_queue_exit(struct request_queue *q)
+{
+	percpu_ref_put(&q->q_usage_counter);
+}
+
+static void blk_queue_usage_counter_release(struct percpu_ref *ref)
+{
+	struct request_queue *q =
+		container_of(ref, struct request_queue, q_usage_counter);
+
+	wake_up_all(&q->mq_freeze_wq);
+}
+
+static void blk_rq_timed_out_timer(struct timer_list *t)
+{
+	struct request_queue *q = from_timer(q, t, timeout);
+
+	kblockd_schedule_work(&q->timeout_work);
+}
+
+static void blk_timeout_work_dummy(struct work_struct *work)
+{
+}
+
+/**
+ * blk_alloc_queue_node - allocate a request queue
+ * @gfp_mask: memory allocation flags
+ * @node_id: NUMA node to allocate memory from
+ * @lock: For legacy queues, pointer to a spinlock that will be used to e.g.
+ *        serialize calls to the legacy .request_fn() callback. Ignored for
+ *	  blk-mq request queues.
+ *
+ * Note: pass the queue lock as the third argument to this function instead of
+ * setting the queue lock pointer explicitly to avoid triggering a sporadic
+ * crash in the blkcg code. This function namely calls blkcg_init_queue() and
+ * the queue lock pointer must be set before blkcg_init_queue() is called.
+ */
+struct request_queue *blk_alloc_queue_node(gfp_t gfp_mask, int node_id,
+					   spinlock_t *lock)
+{
+	struct request_queue *q;
+	int ret;
+
+	q = kmem_cache_alloc_node(blk_requestq_cachep,
+				gfp_mask | __GFP_ZERO, node_id);
+	if (!q)
+		return NULL;
+
+	INIT_LIST_HEAD(&q->queue_head);
+	q->last_merge = NULL;
+	q->end_sector = 0;
+	q->boundary_rq = NULL;
+
+	q->id = ida_simple_get(&blk_queue_ida, 0, 0, gfp_mask);
+	if (q->id < 0)
+		goto fail_q;
+
+	ret = bioset_init(&q->bio_split, BIO_POOL_SIZE, 0, BIOSET_NEED_BVECS);
+	if (ret)
+		goto fail_id;
+
+	q->backing_dev_info = bdi_alloc_node(gfp_mask, node_id);
+	if (!q->backing_dev_info)
+		goto fail_split;
+
+	q->stats = blk_alloc_queue_stats();
+	if (!q->stats)
+		goto fail_stats;
+
+	q->backing_dev_info->ra_pages =
+			(VM_MAX_READAHEAD * 1024) / PAGE_SIZE;
+	q->backing_dev_info->io_pages =
+			(VM_MAX_READAHEAD * 1024) / PAGE_SIZE;
+	q->backing_dev_info->capabilities = BDI_CAP_CGROUP_WRITEBACK;
+	q->backing_dev_info->name = "block";
+	q->node = node_id;
+
+	timer_setup(&q->backing_dev_info->laptop_mode_wb_timer,
+		    laptop_mode_timer_fn, 0);
+	timer_setup(&q->timeout, blk_rq_timed_out_timer, 0);
+	INIT_WORK(&q->timeout_work, blk_timeout_work_dummy);
+	INIT_LIST_HEAD(&q->timeout_list);
+	INIT_LIST_HEAD(&q->icq_list);
+#ifdef CONFIG_BLK_CGROUP
+	INIT_LIST_HEAD(&q->blkg_list);
+#endif
+	INIT_DELAYED_WORK(&q->delay_work, blk_delay_work);
+
+	kobject_init(&q->kobj, &blk_queue_ktype);
+
+#ifdef CONFIG_BLK_DEV_IO_TRACE
+	mutex_init(&q->blk_trace_mutex);
+#endif
+	mutex_init(&q->sysfs_lock);
+	mutex_init(&q->sysfs_dir_lock);
+	spin_lock_init(&q->__queue_lock);
+
+	if (!q->mq_ops)
+		q->queue_lock = lock ? : &q->__queue_lock;
+
+	/*
+	 * A queue starts its life with bypass turned on to avoid
+	 * unnecessary bypass on/off overhead and nasty surprises during
+	 * init.  The initial bypass will be finished when the queue is
+	 * registered by blk_register_queue().
+	 */
+	q->bypass_depth = 1;
+	queue_flag_set_unlocked(QUEUE_FLAG_BYPASS, q);
+
+	init_waitqueue_head(&q->mq_freeze_wq);
+
+	/*
+	 * Init percpu_ref in atomic mode so that it's faster to shutdown.
+	 * See blk_register_queue() for details.
+	 */
+	if (percpu_ref_init(&q->q_usage_counter,
+				blk_queue_usage_counter_release,
+				PERCPU_REF_INIT_ATOMIC, GFP_KERNEL))
+		goto fail_bdi;
+
+	if (blkcg_init_queue(q))
+		goto fail_ref;
+
+	return q;
+
+fail_ref:
+	percpu_ref_exit(&q->q_usage_counter);
+fail_bdi:
+	blk_free_queue_stats(q->stats);
+fail_stats:
+	bdi_put(q->backing_dev_info);
+fail_split:
+	bioset_exit(&q->bio_split);
+fail_id:
+	ida_simple_remove(&blk_queue_ida, q->id);
+fail_q:
+	kmem_cache_free(blk_requestq_cachep, q);
+	return NULL;
+}
+EXPORT_SYMBOL(blk_alloc_queue_node);
+
+/**
+ * blk_init_queue  - prepare a request queue for use with a block device
+ * @rfn:  The function to be called to process requests that have been
+ *        placed on the queue.
+ * @lock: Request queue spin lock
+ *
+ * Description:
+ *    If a block device wishes to use the standard request handling procedures,
+ *    which sorts requests and coalesces adjacent requests, then it must
+ *    call blk_init_queue().  The function @rfn will be called when there
+ *    are requests on the queue that need to be processed.  If the device
+ *    supports plugging, then @rfn may not be called immediately when requests
+ *    are available on the queue, but may be called at some time later instead.
+ *    Plugged queues are generally unplugged when a buffer belonging to one
+ *    of the requests on the queue is needed, or due to memory pressure.
+ *
+ *    @rfn is not required, or even expected, to remove all requests off the
+ *    queue, but only as many as it can handle at a time.  If it does leave
+ *    requests on the queue, it is responsible for arranging that the requests
+ *    get dealt with eventually.
+ *
+ *    The queue spin lock must be held while manipulating the requests on the
+ *    request queue; this lock will be taken also from interrupt context, so irq
+ *    disabling is needed for it.
+ *
+ *    Function returns a pointer to the initialized request queue, or %NULL if
+ *    it didn't succeed.
+ *
+ * Note:
+ *    blk_init_queue() must be paired with a blk_cleanup_queue() call
+ *    when the block device is deactivated (such as at module unload).
+ **/
+
+struct request_queue *blk_init_queue(request_fn_proc *rfn, spinlock_t *lock)
+{
+	return blk_init_queue_node(rfn, lock, NUMA_NO_NODE);
+}
+EXPORT_SYMBOL(blk_init_queue);
+
+struct request_queue *
+blk_init_queue_node(request_fn_proc *rfn, spinlock_t *lock, int node_id)
+{
+	struct request_queue *q;
+
+	q = blk_alloc_queue_node(GFP_KERNEL, node_id, lock);
+	if (!q)
+		return NULL;
+
+	q->request_fn = rfn;
+	if (blk_init_allocated_queue(q) < 0) {
+		blk_cleanup_queue(q);
+		return NULL;
+	}
+
+	return q;
+}
+EXPORT_SYMBOL(blk_init_queue_node);
+
+static blk_qc_t blk_queue_bio(struct request_queue *q, struct bio *bio);
+
+
+int blk_init_allocated_queue(struct request_queue *q)
+{
+	WARN_ON_ONCE(q->mq_ops);
+
+	q->fq = blk_alloc_flush_queue(q, NUMA_NO_NODE, q->cmd_size, GFP_KERNEL);
+	if (!q->fq)
+		return -ENOMEM;
+
+	if (q->init_rq_fn && q->init_rq_fn(q, q->fq->flush_rq, GFP_KERNEL))
+		goto out_free_flush_queue;
+
+	if (blk_init_rl(&q->root_rl, q, GFP_KERNEL))
+		goto out_exit_flush_rq;
+
+	INIT_WORK(&q->timeout_work, blk_timeout_work);
+	q->queue_flags		|= QUEUE_FLAG_DEFAULT;
+
+	/*
+	 * This also sets hw/phys segments, boundary and size
+	 */
+	blk_queue_make_request(q, blk_queue_bio);
+
+	q->sg_reserved_size = INT_MAX;
+
+	if (elevator_init(q))
+		goto out_exit_flush_rq;
+	return 0;
+
+out_exit_flush_rq:
+	if (q->exit_rq_fn)
+		q->exit_rq_fn(q, q->fq->flush_rq);
+out_free_flush_queue:
+	blk_free_flush_queue(q->fq);
+	q->fq = NULL;
+	return -ENOMEM;
+}
+EXPORT_SYMBOL(blk_init_allocated_queue);
+
+bool blk_get_queue(struct request_queue *q)
+{
+	if (likely(!blk_queue_dying(q))) {
+		__blk_get_queue(q);
+		return true;
+	}
+
+	return false;
+}
+EXPORT_SYMBOL(blk_get_queue);
+
+static inline void blk_free_request(struct request_list *rl, struct request *rq)
+{
+	if (rq->rq_flags & RQF_ELVPRIV) {
+		elv_put_request(rl->q, rq);
+		if (rq->elv.icq)
+			put_io_context(rq->elv.icq->ioc);
+	}
+
+	mempool_free(rq, rl->rq_pool);
+}
+
+/*
+ * ioc_batching returns true if the ioc is a valid batching request and
+ * should be given priority access to a request.
+ */
+static inline int ioc_batching(struct request_queue *q, struct io_context *ioc)
+{
+	if (!ioc)
+		return 0;
+
+	/*
+	 * Make sure the process is able to allocate at least 1 request
+	 * even if the batch times out, otherwise we could theoretically
+	 * lose wakeups.
+	 */
+	return ioc->nr_batch_requests == q->nr_batching ||
+		(ioc->nr_batch_requests > 0
+		&& time_before(jiffies, ioc->last_waited + BLK_BATCH_TIME));
+}
+
+/*
+ * ioc_set_batching sets ioc to be a new "batcher" if it is not one. This
+ * will cause the process to be a "batcher" on all queues in the system. This
+ * is the behaviour we want though - once it gets a wakeup it should be given
+ * a nice run.
+ */
+static void ioc_set_batching(struct request_queue *q, struct io_context *ioc)
+{
+	if (!ioc || ioc_batching(q, ioc))
+		return;
+
+	ioc->nr_batch_requests = q->nr_batching;
+	ioc->last_waited = jiffies;
+}
+
+static void __freed_request(struct request_list *rl, int sync)
+{
+	struct request_queue *q = rl->q;
+
+	if (rl->count[sync] < queue_congestion_off_threshold(q))
+		blk_clear_congested(rl, sync);
+
+	if (rl->count[sync] + 1 <= q->nr_requests) {
+		if (waitqueue_active(&rl->wait[sync]))
+			wake_up(&rl->wait[sync]);
+
+		blk_clear_rl_full(rl, sync);
+	}
+}
+
+/*
+ * A request has just been released.  Account for it, update the full and
+ * congestion status, wake up any waiters.   Called under q->queue_lock.
+ */
+static void freed_request(struct request_list *rl, bool sync,
+		req_flags_t rq_flags)
+{
+	struct request_queue *q = rl->q;
+
+	q->nr_rqs[sync]--;
+	rl->count[sync]--;
+	if (rq_flags & RQF_ELVPRIV)
+		q->nr_rqs_elvpriv--;
+
+	__freed_request(rl, sync);
+
+	if (unlikely(rl->starved[sync ^ 1]))
+		__freed_request(rl, sync ^ 1);
+}
+
+int blk_update_nr_requests(struct request_queue *q, unsigned int nr)
+{
+	struct request_list *rl;
+	int on_thresh, off_thresh;
+
+	WARN_ON_ONCE(q->mq_ops);
+
+	spin_lock_irq(q->queue_lock);
+	q->nr_requests = nr;
+	blk_queue_congestion_threshold(q);
+	on_thresh = queue_congestion_on_threshold(q);
+	off_thresh = queue_congestion_off_threshold(q);
+
+	blk_queue_for_each_rl(rl, q) {
+		if (rl->count[BLK_RW_SYNC] >= on_thresh)
+			blk_set_congested(rl, BLK_RW_SYNC);
+		else if (rl->count[BLK_RW_SYNC] < off_thresh)
+			blk_clear_congested(rl, BLK_RW_SYNC);
+
+		if (rl->count[BLK_RW_ASYNC] >= on_thresh)
+			blk_set_congested(rl, BLK_RW_ASYNC);
+		else if (rl->count[BLK_RW_ASYNC] < off_thresh)
+			blk_clear_congested(rl, BLK_RW_ASYNC);
+
+		if (rl->count[BLK_RW_SYNC] >= q->nr_requests) {
+			blk_set_rl_full(rl, BLK_RW_SYNC);
+		} else {
+			blk_clear_rl_full(rl, BLK_RW_SYNC);
+			wake_up(&rl->wait[BLK_RW_SYNC]);
+		}
+
+		if (rl->count[BLK_RW_ASYNC] >= q->nr_requests) {
+			blk_set_rl_full(rl, BLK_RW_ASYNC);
+		} else {
+			blk_clear_rl_full(rl, BLK_RW_ASYNC);
+			wake_up(&rl->wait[BLK_RW_ASYNC]);
+		}
+	}
+
+	spin_unlock_irq(q->queue_lock);
+	return 0;
+}
+
+/**
+ * __get_request - get a free request
+ * @rl: request list to allocate from
+ * @op: operation and flags
+ * @bio: bio to allocate request for (can be %NULL)
+ * @flags: BLQ_MQ_REQ_* flags
+ * @gfp_mask: allocator flags
+ *
+ * Get a free request from @q.  This function may fail under memory
+ * pressure or if @q is dead.
+ *
+ * Must be called with @q->queue_lock held and,
+ * Returns ERR_PTR on failure, with @q->queue_lock held.
+ * Returns request pointer on success, with @q->queue_lock *not held*.
+ */
+static struct request *__get_request(struct request_list *rl, unsigned int op,
+		struct bio *bio, blk_mq_req_flags_t flags, gfp_t gfp_mask)
+{
+	struct request_queue *q = rl->q;
+	struct request *rq;
+	struct elevator_type *et = q->elevator->type;
+	struct io_context *ioc = rq_ioc(bio);
+	struct io_cq *icq = NULL;
+	const bool is_sync = op_is_sync(op);
+	int may_queue;
+	req_flags_t rq_flags = RQF_ALLOCED;
+
+	lockdep_assert_held(q->queue_lock);
+
+	if (unlikely(blk_queue_dying(q)))
+		return ERR_PTR(-ENODEV);
+
+	may_queue = elv_may_queue(q, op);
+	if (may_queue == ELV_MQUEUE_NO)
+		goto rq_starved;
+
+	if (rl->count[is_sync]+1 >= queue_congestion_on_threshold(q)) {
+		if (rl->count[is_sync]+1 >= q->nr_requests) {
+			/*
+			 * The queue will fill after this allocation, so set
+			 * it as full, and mark this process as "batching".
+			 * This process will be allowed to complete a batch of
+			 * requests, others will be blocked.
+			 */
+			if (!blk_rl_full(rl, is_sync)) {
+				ioc_set_batching(q, ioc);
+				blk_set_rl_full(rl, is_sync);
+			} else {
+				if (may_queue != ELV_MQUEUE_MUST
+						&& !ioc_batching(q, ioc)) {
+					/*
+					 * The queue is full and the allocating
+					 * process is not a "batcher", and not
+					 * exempted by the IO scheduler
+					 */
+					return ERR_PTR(-ENOMEM);
+				}
+			}
+		}
+		blk_set_congested(rl, is_sync);
+	}
+
+	/*
+	 * Only allow batching queuers to allocate up to 50% over the defined
+	 * limit of requests, otherwise we could have thousands of requests
+	 * allocated with any setting of ->nr_requests
+	 */
+	if (rl->count[is_sync] >= (3 * q->nr_requests / 2))
+		return ERR_PTR(-ENOMEM);
+
+	q->nr_rqs[is_sync]++;
+	rl->count[is_sync]++;
+	rl->starved[is_sync] = 0;
+
+	/*
+	 * Decide whether the new request will be managed by elevator.  If
+	 * so, mark @rq_flags and increment elvpriv.  Non-zero elvpriv will
+	 * prevent the current elevator from being destroyed until the new
+	 * request is freed.  This guarantees icq's won't be destroyed and
+	 * makes creating new ones safe.
+	 *
+	 * Flush requests do not use the elevator so skip initialization.
+	 * This allows a request to share the flush and elevator data.
+	 *
+	 * Also, lookup icq while holding queue_lock.  If it doesn't exist,
+	 * it will be created after releasing queue_lock.
+	 */
+	if (!op_is_flush(op) && !blk_queue_bypass(q)) {
+		rq_flags |= RQF_ELVPRIV;
+		q->nr_rqs_elvpriv++;
+		if (et->icq_cache && ioc)
+			icq = ioc_lookup_icq(ioc, q);
+	}
+
+	if (blk_queue_io_stat(q))
+		rq_flags |= RQF_IO_STAT;
+	spin_unlock_irq(q->queue_lock);
+
+	/* allocate and init request */
+	rq = mempool_alloc(rl->rq_pool, gfp_mask);
+	if (!rq)
+		goto fail_alloc;
+
+	blk_rq_init(q, rq);
+	blk_rq_set_rl(rq, rl);
+	rq->cmd_flags = op;
+	rq->rq_flags = rq_flags;
+	if (flags & BLK_MQ_REQ_PREEMPT)
+		rq->rq_flags |= RQF_PREEMPT;
+
+	/* init elvpriv */
+	if (rq_flags & RQF_ELVPRIV) {
+		if (unlikely(et->icq_cache && !icq)) {
+			if (ioc)
+				icq = ioc_create_icq(ioc, q, gfp_mask);
+			if (!icq)
+				goto fail_elvpriv;
+		}
+
+		rq->elv.icq = icq;
+		if (unlikely(elv_set_request(q, rq, bio, gfp_mask)))
+			goto fail_elvpriv;
+
+		/* @rq->elv.icq holds io_context until @rq is freed */
+		if (icq)
+			get_io_context(icq->ioc);
+	}
+out:
+	/*
+	 * ioc may be NULL here, and ioc_batching will be false. That's
+	 * OK, if the queue is under the request limit then requests need
+	 * not count toward the nr_batch_requests limit. There will always
+	 * be some limit enforced by BLK_BATCH_TIME.
+	 */
+	if (ioc_batching(q, ioc))
+		ioc->nr_batch_requests--;
+
+	trace_block_getrq(q, bio, op);
+	return rq;
+
+fail_elvpriv:
+	/*
+	 * elvpriv init failed.  ioc, icq and elvpriv aren't mempool backed
+	 * and may fail indefinitely under memory pressure and thus
+	 * shouldn't stall IO.  Treat this request as !elvpriv.  This will
+	 * disturb iosched and blkcg but weird is bettern than dead.
+	 */
+	printk_ratelimited(KERN_WARNING "%s: dev %s: request aux data allocation failed, iosched may be disturbed\n",
+			   __func__, dev_name(q->backing_dev_info->dev));
+
+	rq->rq_flags &= ~RQF_ELVPRIV;
+	rq->elv.icq = NULL;
+
+	spin_lock_irq(q->queue_lock);
+	q->nr_rqs_elvpriv--;
+	spin_unlock_irq(q->queue_lock);
+	goto out;
+
+fail_alloc:
+	/*
+	 * Allocation failed presumably due to memory. Undo anything we
+	 * might have messed up.
+	 *
+	 * Allocating task should really be put onto the front of the wait
+	 * queue, but this is pretty rare.
+	 */
+	spin_lock_irq(q->queue_lock);
+	freed_request(rl, is_sync, rq_flags);
+
+	/*
+	 * in the very unlikely event that allocation failed and no
+	 * requests for this direction was pending, mark us starved so that
+	 * freeing of a request in the other direction will notice
+	 * us. another possible fix would be to split the rq mempool into
+	 * READ and WRITE
+	 */
+rq_starved:
+	if (unlikely(rl->count[is_sync] == 0))
+		rl->starved[is_sync] = 1;
+	return ERR_PTR(-ENOMEM);
+}
+
+/**
+ * get_request - get a free request
+ * @q: request_queue to allocate request from
+ * @op: operation and flags
+ * @bio: bio to allocate request for (can be %NULL)
+ * @flags: BLK_MQ_REQ_* flags.
+ * @gfp: allocator flags
+ *
+ * Get a free request from @q.  If %BLK_MQ_REQ_NOWAIT is set in @flags,
+ * this function keeps retrying under memory pressure and fails iff @q is dead.
+ *
+ * Must be called with @q->queue_lock held and,
+ * Returns ERR_PTR on failure, with @q->queue_lock held.
+ * Returns request pointer on success, with @q->queue_lock *not held*.
+ */
+static struct request *get_request(struct request_queue *q, unsigned int op,
+		struct bio *bio, blk_mq_req_flags_t flags, gfp_t gfp)
+{
+	const bool is_sync = op_is_sync(op);
+	DEFINE_WAIT(wait);
+	struct request_list *rl;
+	struct request *rq;
+
+	lockdep_assert_held(q->queue_lock);
+	WARN_ON_ONCE(q->mq_ops);
+
+	rl = blk_get_rl(q, bio);	/* transferred to @rq on success */
+retry:
+	rq = __get_request(rl, op, bio, flags, gfp);
+	if (!IS_ERR(rq))
+		return rq;
+
+	if (op & REQ_NOWAIT) {
+		blk_put_rl(rl);
+		return ERR_PTR(-EAGAIN);
+	}
+
+	if ((flags & BLK_MQ_REQ_NOWAIT) || unlikely(blk_queue_dying(q))) {
+		blk_put_rl(rl);
+		return rq;
+	}
+
+	/* wait on @rl and retry */
+	prepare_to_wait_exclusive(&rl->wait[is_sync], &wait,
+				  TASK_UNINTERRUPTIBLE);
+
+	trace_block_sleeprq(q, bio, op);
+
+	spin_unlock_irq(q->queue_lock);
+	io_schedule();
+
+	/*
+	 * After sleeping, we become a "batching" process and will be able
+	 * to allocate at least one request, and up to a big batch of them
+	 * for a small period time.  See ioc_batching, ioc_set_batching
+	 */
+	ioc_set_batching(q, current->io_context);
+
+	spin_lock_irq(q->queue_lock);
+	finish_wait(&rl->wait[is_sync], &wait);
+
+	goto retry;
+}
+
+/* flags: BLK_MQ_REQ_PREEMPT and/or BLK_MQ_REQ_NOWAIT. */
+static struct request *blk_old_get_request(struct request_queue *q,
+				unsigned int op, blk_mq_req_flags_t flags)
+{
+	struct request *rq;
+	gfp_t gfp_mask = flags & BLK_MQ_REQ_NOWAIT ? GFP_ATOMIC : GFP_NOIO;
+	int ret = 0;
+
+	WARN_ON_ONCE(q->mq_ops);
+
+	/* create ioc upfront */
+	create_io_context(gfp_mask, q->node);
+
+	ret = blk_queue_enter(q, flags);
+	if (ret)
+		return ERR_PTR(ret);
+	spin_lock_irq(q->queue_lock);
+	rq = get_request(q, op, NULL, flags, gfp_mask);
+	if (IS_ERR(rq)) {
+		spin_unlock_irq(q->queue_lock);
+		blk_queue_exit(q);
+		return rq;
+	}
+
+	/* q->queue_lock is unlocked at this point */
+	rq->__data_len = 0;
+	rq->__sector = (sector_t) -1;
+	rq->bio = rq->biotail = NULL;
+	return rq;
+}
+
+/**
+ * blk_get_request - allocate a request
+ * @q: request queue to allocate a request for
+ * @op: operation (REQ_OP_*) and REQ_* flags, e.g. REQ_SYNC.
+ * @flags: BLK_MQ_REQ_* flags, e.g. BLK_MQ_REQ_NOWAIT.
+ */
+struct request *blk_get_request(struct request_queue *q, unsigned int op,
+				blk_mq_req_flags_t flags)
+{
+	struct request *req;
+
+	WARN_ON_ONCE(op & REQ_NOWAIT);
+	WARN_ON_ONCE(flags & ~(BLK_MQ_REQ_NOWAIT | BLK_MQ_REQ_PREEMPT));
+
+	if (q->mq_ops) {
+		req = blk_mq_alloc_request(q, op, flags);
+		if (!IS_ERR(req) && q->mq_ops->initialize_rq_fn)
+			q->mq_ops->initialize_rq_fn(req);
+	} else {
+		req = blk_old_get_request(q, op, flags);
+		if (!IS_ERR(req) && q->initialize_rq_fn)
+			q->initialize_rq_fn(req);
+	}
+
+	return req;
+}
+EXPORT_SYMBOL(blk_get_request);
+
+/**
+ * blk_requeue_request - put a request back on queue
+ * @q:		request queue where request should be inserted
+ * @rq:		request to be inserted
+ *
+ * Description:
+ *    Drivers often keep queueing requests until the hardware cannot accept
+ *    more, when that condition happens we need to put the request back
+ *    on the queue. Must be called with queue lock held.
+ */
+void blk_requeue_request(struct request_queue *q, struct request *rq)
+{
+	lockdep_assert_held(q->queue_lock);
+	WARN_ON_ONCE(q->mq_ops);
+
+	blk_delete_timer(rq);
+	blk_clear_rq_complete(rq);
+	trace_block_rq_requeue(q, rq);
+	rq_qos_requeue(q, rq);
+
+	if (rq->rq_flags & RQF_QUEUED)
+		blk_queue_end_tag(q, rq);
+
+	BUG_ON(blk_queued_rq(rq));
+
+	elv_requeue_request(q, rq);
+}
+EXPORT_SYMBOL(blk_requeue_request);
+
+static void add_acct_request(struct request_queue *q, struct request *rq,
+			     int where)
+{
+	blk_account_io_start(rq, true);
+	__elv_add_request(q, rq, where);
+}
+
+static void part_round_stats_single(struct request_queue *q, int cpu,
+				    struct hd_struct *part, unsigned long now,
+				    unsigned int inflight)
+{
+	if (inflight) {
+		__part_stat_add(cpu, part, time_in_queue,
+				inflight * (now - part->stamp));
+		__part_stat_add(cpu, part, io_ticks, (now - part->stamp));
+	}
+	part->stamp = now;
+}
+
+/**
+ * part_round_stats() - Round off the performance stats on a struct disk_stats.
+ * @q: target block queue
+ * @cpu: cpu number for stats access
+ * @part: target partition
+ *
+ * The average IO queue length and utilisation statistics are maintained
+ * by observing the current state of the queue length and the amount of
+ * time it has been in this state for.
+ *
+ * Normally, that accounting is done on IO completion, but that can result
+ * in more than a second's worth of IO being accounted for within any one
+ * second, leading to >100% utilisation.  To deal with that, we call this
+ * function to do a round-off before returning the results when reading
+ * /proc/diskstats.  This accounts immediately for all queue usage up to
+ * the current jiffies and restarts the counters again.
+ */
+void part_round_stats(struct request_queue *q, int cpu, struct hd_struct *part)
+{
+	struct hd_struct *part2 = NULL;
+	unsigned long now = jiffies;
+	unsigned int inflight[2];
+	int stats = 0;
+
+	if (part->stamp != now)
+		stats |= 1;
+
+	if (part->partno) {
+		part2 = &part_to_disk(part)->part0;
+		if (part2->stamp != now)
+			stats |= 2;
+	}
+
+	if (!stats)
+		return;
+
+	part_in_flight(q, part, inflight);
+
+	if (stats & 2)
+		part_round_stats_single(q, cpu, part2, now, inflight[1]);
+	if (stats & 1)
+		part_round_stats_single(q, cpu, part, now, inflight[0]);
+}
+EXPORT_SYMBOL_GPL(part_round_stats);
+
+#ifdef CONFIG_PM
+static void blk_pm_put_request(struct request *rq)
+{
+	if (rq->q->dev && !(rq->rq_flags & RQF_PM) && !--rq->q->nr_pending)
+		pm_runtime_mark_last_busy(rq->q->dev);
+}
+#else
+static inline void blk_pm_put_request(struct request *rq) {}
+#endif
+
+void __blk_put_request(struct request_queue *q, struct request *req)
+{
+	req_flags_t rq_flags = req->rq_flags;
+
+	if (unlikely(!q))
+		return;
+
+	if (q->mq_ops) {
+		blk_mq_free_request(req);
+		return;
+	}
+
+	lockdep_assert_held(q->queue_lock);
+
+	blk_req_zone_write_unlock(req);
+	blk_pm_put_request(req);
+
+	elv_completed_request(q, req);
+
+	/* this is a bio leak */
+	WARN_ON(req->bio != NULL);
+
+	rq_qos_done(q, req);
+
+	/*
+	 * Request may not have originated from ll_rw_blk. if not,
+	 * it didn't come out of our reserved rq pools
+	 */
+	if (rq_flags & RQF_ALLOCED) {
+		struct request_list *rl = blk_rq_rl(req);
+		bool sync = op_is_sync(req->cmd_flags);
+
+		BUG_ON(!list_empty(&req->queuelist));
+		BUG_ON(ELV_ON_HASH(req));
+
+		blk_free_request(rl, req);
+		freed_request(rl, sync, rq_flags);
+		blk_put_rl(rl);
+		blk_queue_exit(q);
+	}
+}
+EXPORT_SYMBOL_GPL(__blk_put_request);
+
+void blk_put_request(struct request *req)
+{
+	struct request_queue *q = req->q;
+
+	if (q->mq_ops)
+		blk_mq_free_request(req);
+	else {
+		unsigned long flags;
+
+		spin_lock_irqsave(q->queue_lock, flags);
+		__blk_put_request(q, req);
+		spin_unlock_irqrestore(q->queue_lock, flags);
+	}
+}
+EXPORT_SYMBOL(blk_put_request);
+
+bool bio_attempt_back_merge(struct request_queue *q, struct request *req,
+			    struct bio *bio)
+{
+	const int ff = bio->bi_opf & REQ_FAILFAST_MASK;
+
+	if (!ll_back_merge_fn(q, req, bio))
+		return false;
+
+	trace_block_bio_backmerge(q, req, bio);
+
+	if ((req->cmd_flags & REQ_FAILFAST_MASK) != ff)
+		blk_rq_set_mixed_merge(req);
+
+	req->biotail->bi_next = bio;
+	req->biotail = bio;
+	req->__data_len += bio->bi_iter.bi_size;
+	req->ioprio = ioprio_best(req->ioprio, bio_prio(bio));
+
+	blk_account_io_start(req, false);
+	return true;
+}
+
+bool bio_attempt_front_merge(struct request_queue *q, struct request *req,
+			     struct bio *bio)
+{
+	const int ff = bio->bi_opf & REQ_FAILFAST_MASK;
+
+	if (!ll_front_merge_fn(q, req, bio))
+		return false;
+
+	trace_block_bio_frontmerge(q, req, bio);
+
+	if ((req->cmd_flags & REQ_FAILFAST_MASK) != ff)
+		blk_rq_set_mixed_merge(req);
+
+	bio->bi_next = req->bio;
+	req->bio = bio;
+
+	req->__sector = bio->bi_iter.bi_sector;
+	req->__data_len += bio->bi_iter.bi_size;
+	req->ioprio = ioprio_best(req->ioprio, bio_prio(bio));
+
+	blk_account_io_start(req, false);
+	return true;
+}
+
+bool bio_attempt_discard_merge(struct request_queue *q, struct request *req,
+		struct bio *bio)
+{
+	unsigned short segments = blk_rq_nr_discard_segments(req);
+
+	if (segments >= queue_max_discard_segments(q))
+		goto no_merge;
+	if (blk_rq_sectors(req) + bio_sectors(bio) >
+	    blk_rq_get_max_sectors(req, blk_rq_pos(req)))
+		goto no_merge;
+
+	req->biotail->bi_next = bio;
+	req->biotail = bio;
+	req->__data_len += bio->bi_iter.bi_size;
+	req->ioprio = ioprio_best(req->ioprio, bio_prio(bio));
+	req->nr_phys_segments = segments + 1;
+
+	blk_account_io_start(req, false);
+	return true;
+no_merge:
+	req_set_nomerge(q, req);
+	return false;
+}
+
+/**
+ * blk_attempt_plug_merge - try to merge with %current's plugged list
+ * @q: request_queue new bio is being queued at
+ * @bio: new bio being queued
+ * @request_count: out parameter for number of traversed plugged requests
+ * @same_queue_rq: pointer to &struct request that gets filled in when
+ * another request associated with @q is found on the plug list
+ * (optional, may be %NULL)
+ *
+ * Determine whether @bio being queued on @q can be merged with a request
+ * on %current's plugged list.  Returns %true if merge was successful,
+ * otherwise %false.
+ *
+ * Plugging coalesces IOs from the same issuer for the same purpose without
+ * going through @q->queue_lock.  As such it's more of an issuing mechanism
+ * than scheduling, and the request, while may have elvpriv data, is not
+ * added on the elevator at this point.  In addition, we don't have
+ * reliable access to the elevator outside queue lock.  Only check basic
+ * merging parameters without querying the elevator.
+ *
+ * Caller must ensure !blk_queue_nomerges(q) beforehand.
+ */
+bool blk_attempt_plug_merge(struct request_queue *q, struct bio *bio,
+			    unsigned int *request_count,
+			    struct request **same_queue_rq)
+{
+	struct blk_plug *plug;
+	struct request *rq;
+	struct list_head *plug_list;
+
+	plug = current->plug;
+	if (!plug)
+		return false;
+	*request_count = 0;
+
+	if (q->mq_ops)
+		plug_list = &plug->mq_list;
+	else
+		plug_list = &plug->list;
+
+	list_for_each_entry_reverse(rq, plug_list, queuelist) {
+		bool merged = false;
+
+		if (rq->q == q) {
+			(*request_count)++;
+			/*
+			 * Only blk-mq multiple hardware queues case checks the
+			 * rq in the same queue, there should be only one such
+			 * rq in a queue
+			 **/
+			if (same_queue_rq)
+				*same_queue_rq = rq;
+		}
+
+		if (rq->q != q || !blk_rq_merge_ok(rq, bio))
+			continue;
+
+		switch (blk_try_merge(rq, bio)) {
+		case ELEVATOR_BACK_MERGE:
+			merged = bio_attempt_back_merge(q, rq, bio);
+			break;
+		case ELEVATOR_FRONT_MERGE:
+			merged = bio_attempt_front_merge(q, rq, bio);
+			break;
+		case ELEVATOR_DISCARD_MERGE:
+			merged = bio_attempt_discard_merge(q, rq, bio);
+			break;
+		default:
+			break;
+		}
+
+		if (merged)
+			return true;
+	}
+
+	return false;
+}
+
+unsigned int blk_plug_queued_count(struct request_queue *q)
+{
+	struct blk_plug *plug;
+	struct request *rq;
+	struct list_head *plug_list;
+	unsigned int ret = 0;
+
+	plug = current->plug;
+	if (!plug)
+		goto out;
+
+	if (q->mq_ops)
+		plug_list = &plug->mq_list;
+	else
+		plug_list = &plug->list;
+
+	list_for_each_entry(rq, plug_list, queuelist) {
+		if (rq->q == q)
+			ret++;
+	}
+out:
+	return ret;
+}
+
+void blk_init_request_from_bio(struct request *req, struct bio *bio)
+{
+	struct io_context *ioc = rq_ioc(bio);
+
+	if (bio->bi_opf & REQ_RAHEAD)
+		req->cmd_flags |= REQ_FAILFAST_MASK;
+
+	req->__sector = bio->bi_iter.bi_sector;
+	if (ioprio_valid(bio_prio(bio)))
+		req->ioprio = bio_prio(bio);
+	else if (ioc)
+		req->ioprio = ioc->ioprio;
+	else
+		req->ioprio = IOPRIO_PRIO_VALUE(IOPRIO_CLASS_NONE, 0);
+	req->write_hint = bio->bi_write_hint;
+	blk_rq_bio_prep(req->q, req, bio);
+}
+EXPORT_SYMBOL_GPL(blk_init_request_from_bio);
+
+static blk_qc_t blk_queue_bio(struct request_queue *q, struct bio *bio)
+{
+	struct blk_plug *plug;
+	int where = ELEVATOR_INSERT_SORT;
+	struct request *req, *free;
+	unsigned int request_count = 0;
+
+	/*
+	 * low level driver can indicate that it wants pages above a
+	 * certain limit bounced to low memory (ie for highmem, or even
+	 * ISA dma in theory)
+	 */
+	blk_queue_bounce(q, &bio);
+
+	blk_queue_split(q, &bio);
+
+	if (!bio_integrity_prep(bio))
+		return BLK_QC_T_NONE;
+
+	if (op_is_flush(bio->bi_opf)) {
+		spin_lock_irq(q->queue_lock);
+		where = ELEVATOR_INSERT_FLUSH;
+		goto get_rq;
+	}
+
+	/*
+	 * Check if we can merge with the plugged list before grabbing
+	 * any locks.
+	 */
+	if (!blk_queue_nomerges(q)) {
+		if (blk_attempt_plug_merge(q, bio, &request_count, NULL))
+			return BLK_QC_T_NONE;
+	} else
+		request_count = blk_plug_queued_count(q);
+
+	spin_lock_irq(q->queue_lock);
+
+	switch (elv_merge(q, &req, bio)) {
+	case ELEVATOR_BACK_MERGE:
+		if (!bio_attempt_back_merge(q, req, bio))
+			break;
+		elv_bio_merged(q, req, bio);
+		free = attempt_back_merge(q, req);
+		if (free)
+			__blk_put_request(q, free);
+		else
+			elv_merged_request(q, req, ELEVATOR_BACK_MERGE);
+		goto out_unlock;
+	case ELEVATOR_FRONT_MERGE:
+		if (!bio_attempt_front_merge(q, req, bio))
+			break;
+		elv_bio_merged(q, req, bio);
+		free = attempt_front_merge(q, req);
+		if (free)
+			__blk_put_request(q, free);
+		else
+			elv_merged_request(q, req, ELEVATOR_FRONT_MERGE);
+		goto out_unlock;
+	default:
+		break;
+	}
+
+get_rq:
+	rq_qos_throttle(q, bio, q->queue_lock);
+
+	/*
+	 * Grab a free request. This is might sleep but can not fail.
+	 * Returns with the queue unlocked.
+	 */
+	blk_queue_enter_live(q);
+	req = get_request(q, bio->bi_opf, bio, 0, GFP_NOIO);
+	if (IS_ERR(req)) {
+		blk_queue_exit(q);
+		rq_qos_cleanup(q, bio);
+		if (PTR_ERR(req) == -ENOMEM)
+			bio->bi_status = BLK_STS_RESOURCE;
+		else
+			bio->bi_status = BLK_STS_IOERR;
+		bio_endio(bio);
+		goto out_unlock;
+	}
+
+	rq_qos_track(q, req, bio);
+
+	/*
+	 * After dropping the lock and possibly sleeping here, our request
+	 * may now be mergeable after it had proven unmergeable (above).
+	 * We don't worry about that case for efficiency. It won't happen
+	 * often, and the elevators are able to handle it.
+	 */
+	blk_init_request_from_bio(req, bio);
+
+	if (test_bit(QUEUE_FLAG_SAME_COMP, &q->queue_flags))
+		req->cpu = raw_smp_processor_id();
+
+	plug = current->plug;
+	if (plug) {
+		/*
+		 * If this is the first request added after a plug, fire
+		 * of a plug trace.
+		 *
+		 * @request_count may become stale because of schedule
+		 * out, so check plug list again.
+		 */
+		if (!request_count || list_empty(&plug->list))
+			trace_block_plug(q);
+		else {
+			struct request *last = list_entry_rq(plug->list.prev);
+			if (request_count >= BLK_MAX_REQUEST_COUNT ||
+			    blk_rq_bytes(last) >= BLK_PLUG_FLUSH_SIZE) {
+				blk_flush_plug_list(plug, false);
+				trace_block_plug(q);
+			}
+		}
+		list_add_tail(&req->queuelist, &plug->list);
+		blk_account_io_start(req, true);
+	} else {
+		spin_lock_irq(q->queue_lock);
+		add_acct_request(q, req, where);
+		__blk_run_queue(q);
+out_unlock:
+		spin_unlock_irq(q->queue_lock);
+	}
+
+	return BLK_QC_T_NONE;
+}
+
+static void handle_bad_sector(struct bio *bio, sector_t maxsector)
+{
+	char b[BDEVNAME_SIZE];
+
+	printk(KERN_INFO "attempt to access beyond end of device\n");
+	printk(KERN_INFO "%s: rw=%d, want=%Lu, limit=%Lu\n",
+			bio_devname(bio, b), bio->bi_opf,
+			(unsigned long long)bio_end_sector(bio),
+			(long long)maxsector);
+}
+
+#ifdef CONFIG_FAIL_MAKE_REQUEST
+
+static DECLARE_FAULT_ATTR(fail_make_request);
+
+static int __init setup_fail_make_request(char *str)
+{
+	return setup_fault_attr(&fail_make_request, str);
+}
+__setup("fail_make_request=", setup_fail_make_request);
+
+static bool should_fail_request(struct hd_struct *part, unsigned int bytes)
+{
+	return part->make_it_fail && should_fail(&fail_make_request, bytes);
+}
+
+static int __init fail_make_request_debugfs(void)
+{
+	struct dentry *dir = fault_create_debugfs_attr("fail_make_request",
+						NULL, &fail_make_request);
+
+	return PTR_ERR_OR_ZERO(dir);
+}
+
+late_initcall(fail_make_request_debugfs);
+
+#else /* CONFIG_FAIL_MAKE_REQUEST */
+
+static inline bool should_fail_request(struct hd_struct *part,
+					unsigned int bytes)
+{
+	return false;
+}
+
+#endif /* CONFIG_FAIL_MAKE_REQUEST */
+
+static inline bool bio_check_ro(struct bio *bio, struct hd_struct *part)
+{
+	const int op = bio_op(bio);
+
+	if (part->policy && op_is_write(op)) {
+		char b[BDEVNAME_SIZE];
+
+		if (op_is_flush(bio->bi_opf) && !bio_sectors(bio))
+			return false;
+
+		WARN_ONCE(1,
+		       "generic_make_request: Trying to write "
+			"to read-only block-device %s (partno %d)\n",
+			bio_devname(bio, b), part->partno);
+		/* Older lvm-tools actually trigger this */
+		return false;
+	}
+
+	return false;
+}
+
+static noinline int should_fail_bio(struct bio *bio)
+{
+	if (should_fail_request(&bio->bi_disk->part0, bio->bi_iter.bi_size))
+		return -EIO;
+	return 0;
+}
+ALLOW_ERROR_INJECTION(should_fail_bio, ERRNO);
+
+/*
+ * Check whether this bio extends beyond the end of the device or partition.
+ * This may well happen - the kernel calls bread() without checking the size of
+ * the device, e.g., when mounting a file system.
+ */
+static inline int bio_check_eod(struct bio *bio, sector_t maxsector)
+{
+	unsigned int nr_sectors = bio_sectors(bio);
+
+	if (nr_sectors && maxsector &&
+	    (nr_sectors > maxsector ||
+	     bio->bi_iter.bi_sector > maxsector - nr_sectors)) {
+		handle_bad_sector(bio, maxsector);
+		return -EIO;
+	}
+	return 0;
+}
+
+/*
+ * Remap block n of partition p to block n+start(p) of the disk.
+ */
+static inline int blk_partition_remap(struct bio *bio)
+{
+	struct hd_struct *p;
+	int ret = -EIO;
+
+	rcu_read_lock();
+	p = __disk_get_part(bio->bi_disk, bio->bi_partno);
+	if (unlikely(!p))
+		goto out;
+	if (unlikely(should_fail_request(p, bio->bi_iter.bi_size)))
+		goto out;
+	if (unlikely(bio_check_ro(bio, p)))
+		goto out;
+
+	/*
+	 * Zone reset does not include bi_size so bio_sectors() is always 0.
+	 * Include a test for the reset op code and perform the remap if needed.
+	 */
+	if (bio_sectors(bio) || bio_op(bio) == REQ_OP_ZONE_RESET) {
+		if (bio_check_eod(bio, part_nr_sects_read(p)))
+			goto out;
+		bio->bi_iter.bi_sector += p->start_sect;
+		trace_block_bio_remap(bio->bi_disk->queue, bio, part_devt(p),
+				      bio->bi_iter.bi_sector - p->start_sect);
+	}
+	bio->bi_partno = 0;
+	ret = 0;
+out:
+	rcu_read_unlock();
+	return ret;
+}
+
+static noinline_for_stack bool
+generic_make_request_checks(struct bio *bio)
+{
+	struct request_queue *q;
+	int nr_sectors = bio_sectors(bio);
+	blk_status_t status = BLK_STS_IOERR;
+	char b[BDEVNAME_SIZE];
+
+	might_sleep();
+
+	q = bio->bi_disk->queue;
+	if (unlikely(!q)) {
+		printk(KERN_ERR
+		       "generic_make_request: Trying to access "
+			"nonexistent block-device %s (%Lu)\n",
+			bio_devname(bio, b), (long long)bio->bi_iter.bi_sector);
+		goto end_io;
+	}
+
+	/*
+	 * For a REQ_NOWAIT based request, return -EOPNOTSUPP
+	 * if queue is not a request based queue.
+	 */
+	if ((bio->bi_opf & REQ_NOWAIT) && !queue_is_rq_based(q))
+		goto not_supported;
+
+	if (should_fail_bio(bio))
+		goto end_io;
+
+	if (bio->bi_partno) {
+		if (unlikely(blk_partition_remap(bio)))
+			goto end_io;
+	} else {
+		if (unlikely(bio_check_ro(bio, &bio->bi_disk->part0)))
+			goto end_io;
+		if (unlikely(bio_check_eod(bio, get_capacity(bio->bi_disk))))
+			goto end_io;
+	}
+
+	/*
+	 * Filter flush bio's early so that make_request based
+	 * drivers without flush support don't have to worry
+	 * about them.
+	 */
+	if (op_is_flush(bio->bi_opf) &&
+	    !test_bit(QUEUE_FLAG_WC, &q->queue_flags)) {
+		bio->bi_opf &= ~(REQ_PREFLUSH | REQ_FUA);
+		if (!nr_sectors) {
+			status = BLK_STS_OK;
+			goto end_io;
+		}
+	}
+
+	switch (bio_op(bio)) {
+	case REQ_OP_DISCARD:
+		if (!blk_queue_discard(q))
+			goto not_supported;
+		break;
+	case REQ_OP_SECURE_ERASE:
+		if (!blk_queue_secure_erase(q))
+			goto not_supported;
+		break;
+	case REQ_OP_WRITE_SAME:
+		if (!q->limits.max_write_same_sectors)
+			goto not_supported;
+		break;
+	case REQ_OP_ZONE_REPORT:
+	case REQ_OP_ZONE_RESET:
+		if (!blk_queue_is_zoned(q))
+			goto not_supported;
+		break;
+	case REQ_OP_WRITE_ZEROES:
+		if (!q->limits.max_write_zeroes_sectors)
+			goto not_supported;
+		break;
+	default:
+		break;
+	}
+
+	/*
+	 * Various block parts want %current->io_context and lazy ioc
+	 * allocation ends up trading a lot of pain for a small amount of
+	 * memory.  Just allocate it upfront.  This may fail and block
+	 * layer knows how to live with it.
+	 */
+	create_io_context(GFP_ATOMIC, q->node);
+
+	if (!blkcg_bio_issue_check(q, bio))
+		return false;
+
+	if (!bio_flagged(bio, BIO_TRACE_COMPLETION)) {
+		trace_block_bio_queue(q, bio);
+		/* Now that enqueuing has been traced, we need to trace
+		 * completion as well.
+		 */
+		bio_set_flag(bio, BIO_TRACE_COMPLETION);
+	}
+	return true;
+
+not_supported:
+	status = BLK_STS_NOTSUPP;
+end_io:
+	bio->bi_status = status;
+	bio_endio(bio);
+	return false;
+}
+
+/**
+ * generic_make_request - hand a buffer to its device driver for I/O
+ * @bio:  The bio describing the location in memory and on the device.
+ *
+ * generic_make_request() is used to make I/O requests of block
+ * devices. It is passed a &struct bio, which describes the I/O that needs
+ * to be done.
+ *
+ * generic_make_request() does not return any status.  The
+ * success/failure status of the request, along with notification of
+ * completion, is delivered asynchronously through the bio->bi_end_io
+ * function described (one day) else where.
+ *
+ * The caller of generic_make_request must make sure that bi_io_vec
+ * are set to describe the memory buffer, and that bi_dev and bi_sector are
+ * set to describe the device address, and the
+ * bi_end_io and optionally bi_private are set to describe how
+ * completion notification should be signaled.
+ *
+ * generic_make_request and the drivers it calls may use bi_next if this
+ * bio happens to be merged with someone else, and may resubmit the bio to
+ * a lower device by calling into generic_make_request recursively, which
+ * means the bio should NOT be touched after the call to ->make_request_fn.
+ */
+blk_qc_t generic_make_request(struct bio *bio)
+{
+	/*
+	 * bio_list_on_stack[0] contains bios submitted by the current
+	 * make_request_fn.
+	 * bio_list_on_stack[1] contains bios that were submitted before
+	 * the current make_request_fn, but that haven't been processed
+	 * yet.
+	 */
+	struct bio_list bio_list_on_stack[2];
+	blk_mq_req_flags_t flags = 0;
+	struct request_queue *q = bio->bi_disk->queue;
+	blk_qc_t ret = BLK_QC_T_NONE;
+
+	if (bio->bi_opf & REQ_NOWAIT)
+		flags = BLK_MQ_REQ_NOWAIT;
+	if (bio_flagged(bio, BIO_QUEUE_ENTERED))
+		blk_queue_enter_live(q);
+	else if (blk_queue_enter(q, flags) < 0) {
+		if (!blk_queue_dying(q) && (bio->bi_opf & REQ_NOWAIT))
+			bio_wouldblock_error(bio);
+		else
+			bio_io_error(bio);
+		return ret;
+	}
+
+	if (!generic_make_request_checks(bio))
+		goto out;
+
+	/*
+	 * We only want one ->make_request_fn to be active at a time, else
+	 * stack usage with stacked devices could be a problem.  So use
+	 * current->bio_list to keep a list of requests submited by a
+	 * make_request_fn function.  current->bio_list is also used as a
+	 * flag to say if generic_make_request is currently active in this
+	 * task or not.  If it is NULL, then no make_request is active.  If
+	 * it is non-NULL, then a make_request is active, and new requests
+	 * should be added at the tail
+	 */
+	if (current->bio_list) {
+		bio_list_add(&current->bio_list[0], bio);
+		goto out;
+	}
+
+	/* following loop may be a bit non-obvious, and so deserves some
+	 * explanation.
+	 * Before entering the loop, bio->bi_next is NULL (as all callers
+	 * ensure that) so we have a list with a single bio.
+	 * We pretend that we have just taken it off a longer list, so
+	 * we assign bio_list to a pointer to the bio_list_on_stack,
+	 * thus initialising the bio_list of new bios to be
+	 * added.  ->make_request() may indeed add some more bios
+	 * through a recursive call to generic_make_request.  If it
+	 * did, we find a non-NULL value in bio_list and re-enter the loop
+	 * from the top.  In this case we really did just take the bio
+	 * of the top of the list (no pretending) and so remove it from
+	 * bio_list, and call into ->make_request() again.
+	 */
+	BUG_ON(bio->bi_next);
+	bio_list_init(&bio_list_on_stack[0]);
+	current->bio_list = bio_list_on_stack;
+	do {
+		bool enter_succeeded = true;
+
+		if (unlikely(q != bio->bi_disk->queue)) {
+			if (q)
+				blk_queue_exit(q);
+			q = bio->bi_disk->queue;
+			flags = 0;
+			if (bio->bi_opf & REQ_NOWAIT)
+				flags = BLK_MQ_REQ_NOWAIT;
+			if (blk_queue_enter(q, flags) < 0)
+				enter_succeeded = false;
+		}
+
+		if (enter_succeeded) {
+			struct bio_list lower, same;
+
+			/* Create a fresh bio_list for all subordinate requests */
+			bio_list_on_stack[1] = bio_list_on_stack[0];
+			bio_list_init(&bio_list_on_stack[0]);
+			ret = q->make_request_fn(q, bio);
+
+			/* sort new bios into those for a lower level
+			 * and those for the same level
+			 */
+			bio_list_init(&lower);
+			bio_list_init(&same);
+			while ((bio = bio_list_pop(&bio_list_on_stack[0])) != NULL)
+				if (q == bio->bi_disk->queue)
+					bio_list_add(&same, bio);
+				else
+					bio_list_add(&lower, bio);
+			/* now assemble so we handle the lowest level first */
+			bio_list_merge(&bio_list_on_stack[0], &lower);
+			bio_list_merge(&bio_list_on_stack[0], &same);
+			bio_list_merge(&bio_list_on_stack[0], &bio_list_on_stack[1]);
+		} else {
+			if (unlikely(!blk_queue_dying(q) &&
+					(bio->bi_opf & REQ_NOWAIT)))
+				bio_wouldblock_error(bio);
+			else
+				bio_io_error(bio);
+			q = NULL;
+		}
+		bio = bio_list_pop(&bio_list_on_stack[0]);
+	} while (bio);
+	current->bio_list = NULL; /* deactivate */
+
+out:
+	if (q)
+		blk_queue_exit(q);
+	return ret;
+}
+EXPORT_SYMBOL(generic_make_request);
+
+/**
+ * direct_make_request - hand a buffer directly to its device driver for I/O
+ * @bio:  The bio describing the location in memory and on the device.
+ *
+ * This function behaves like generic_make_request(), but does not protect
+ * against recursion.  Must only be used if the called driver is known
+ * to not call generic_make_request (or direct_make_request) again from
+ * its make_request function.  (Calling direct_make_request again from
+ * a workqueue is perfectly fine as that doesn't recurse).
+ */
+blk_qc_t direct_make_request(struct bio *bio)
+{
+	struct request_queue *q = bio->bi_disk->queue;
+	bool nowait = bio->bi_opf & REQ_NOWAIT;
+	blk_qc_t ret;
+
+	if (!generic_make_request_checks(bio))
+		return BLK_QC_T_NONE;
+
+	if (unlikely(blk_queue_enter(q, nowait ? BLK_MQ_REQ_NOWAIT : 0))) {
+		if (nowait && !blk_queue_dying(q))
+			bio->bi_status = BLK_STS_AGAIN;
+		else
+			bio->bi_status = BLK_STS_IOERR;
+		bio_endio(bio);
+		return BLK_QC_T_NONE;
+	}
+
+	ret = q->make_request_fn(q, bio);
+	blk_queue_exit(q);
+	return ret;
+}
+EXPORT_SYMBOL_GPL(direct_make_request);
+
+/**
+ * submit_bio - submit a bio to the block device layer for I/O
+ * @bio: The &struct bio which describes the I/O
+ *
+ * submit_bio() is very similar in purpose to generic_make_request(), and
+ * uses that function to do most of the work. Both are fairly rough
+ * interfaces; @bio must be presetup and ready for I/O.
+ *
+ */
+blk_qc_t submit_bio(struct bio *bio)
+{
+	/*
+	 * If it's a regular read/write or a barrier with data attached,
+	 * go through the normal accounting stuff before submission.
+	 */
+	if (bio_has_data(bio)) {
+		unsigned int count;
+
+		if (unlikely(bio_op(bio) == REQ_OP_WRITE_SAME))
+			count = queue_logical_block_size(bio->bi_disk->queue) >> 9;
+		else
+			count = bio_sectors(bio);
+
+		if (op_is_write(bio_op(bio))) {
+			count_vm_events(PGPGOUT, count);
+		} else {
+			task_io_account_read(bio->bi_iter.bi_size);
+			count_vm_events(PGPGIN, count);
+		}
+
+		if (unlikely(block_dump)) {
+			char b[BDEVNAME_SIZE];
+			printk(KERN_DEBUG "%s(%d): %s block %Lu on %s (%u sectors)\n",
+			current->comm, task_pid_nr(current),
+				op_is_write(bio_op(bio)) ? "WRITE" : "READ",
+				(unsigned long long)bio->bi_iter.bi_sector,
+				bio_devname(bio, b), count);
+		}
+	}
+
+	return generic_make_request(bio);
+}
+EXPORT_SYMBOL(submit_bio);
+
+bool blk_poll(struct request_queue *q, blk_qc_t cookie)
+{
+	if (!q->poll_fn || !blk_qc_t_valid(cookie))
+		return false;
+
+	if (current->plug)
+		blk_flush_plug_list(current->plug, false);
+	return q->poll_fn(q, cookie);
+}
+EXPORT_SYMBOL_GPL(blk_poll);
+
+/**
+ * blk_cloned_rq_check_limits - Helper function to check a cloned request
+ *                              for new the queue limits
+ * @q:  the queue
+ * @rq: the request being checked
+ *
+ * Description:
+ *    @rq may have been made based on weaker limitations of upper-level queues
+ *    in request stacking drivers, and it may violate the limitation of @q.
+ *    Since the block layer and the underlying device driver trust @rq
+ *    after it is inserted to @q, it should be checked against @q before
+ *    the insertion using this generic function.
+ *
+ *    Request stacking drivers like request-based dm may change the queue
+ *    limits when retrying requests on other queues. Those requests need
+ *    to be checked against the new queue limits again during dispatch.
+ */
+static int blk_cloned_rq_check_limits(struct request_queue *q,
+				      struct request *rq)
+{
+	if (blk_rq_sectors(rq) > blk_queue_get_max_sectors(q, req_op(rq))) {
+		printk(KERN_ERR "%s: over max size limit.\n", __func__);
+		return -EIO;
+	}
+
+	/*
+	 * queue's settings related to segment counting like q->bounce_pfn
+	 * may differ from that of other stacking queues.
+	 * Recalculate it to check the request correctly on this queue's
+	 * limitation.
+	 */
+	blk_recalc_rq_segments(rq);
+	if (rq->nr_phys_segments > queue_max_segments(q)) {
+		printk(KERN_ERR "%s: over max segments limit.\n", __func__);
+		return -EIO;
+	}
+
+	return 0;
+}
+
+/**
+ * blk_insert_cloned_request - Helper for stacking drivers to submit a request
+ * @q:  the queue to submit the request
+ * @rq: the request being queued
+ */
+blk_status_t blk_insert_cloned_request(struct request_queue *q, struct request *rq)
+{
+	unsigned long flags;
+	int where = ELEVATOR_INSERT_BACK;
+
+	if (blk_cloned_rq_check_limits(q, rq))
+		return BLK_STS_IOERR;
+
+	if (rq->rq_disk &&
+	    should_fail_request(&rq->rq_disk->part0, blk_rq_bytes(rq)))
+		return BLK_STS_IOERR;
+
+	if (q->mq_ops) {
+		if (blk_queue_io_stat(q))
+			blk_account_io_start(rq, true);
+		/*
+		 * Since we have a scheduler attached on the top device,
+		 * bypass a potential scheduler on the bottom device for
+		 * insert.
+		 */
+		return blk_mq_request_issue_directly(rq);
+	}
+
+	spin_lock_irqsave(q->queue_lock, flags);
+	if (unlikely(blk_queue_dying(q))) {
+		spin_unlock_irqrestore(q->queue_lock, flags);
+		return BLK_STS_IOERR;
+	}
+
+	/*
+	 * Submitting request must be dequeued before calling this function
+	 * because it will be linked to another request_queue
+	 */
+	BUG_ON(blk_queued_rq(rq));
+
+	if (op_is_flush(rq->cmd_flags))
+		where = ELEVATOR_INSERT_FLUSH;
+
+	add_acct_request(q, rq, where);
+	if (where == ELEVATOR_INSERT_FLUSH)
+		__blk_run_queue(q);
+	spin_unlock_irqrestore(q->queue_lock, flags);
+
+	return BLK_STS_OK;
+}
+EXPORT_SYMBOL_GPL(blk_insert_cloned_request);
+
+/**
+ * blk_rq_err_bytes - determine number of bytes till the next failure boundary
+ * @rq: request to examine
+ *
+ * Description:
+ *     A request could be merge of IOs which require different failure
+ *     handling.  This function determines the number of bytes which
+ *     can be failed from the beginning of the request without
+ *     crossing into area which need to be retried further.
+ *
+ * Return:
+ *     The number of bytes to fail.
+ */
+unsigned int blk_rq_err_bytes(const struct request *rq)
+{
+	unsigned int ff = rq->cmd_flags & REQ_FAILFAST_MASK;
+	unsigned int bytes = 0;
+	struct bio *bio;
+
+	if (!(rq->rq_flags & RQF_MIXED_MERGE))
+		return blk_rq_bytes(rq);
+
+	/*
+	 * Currently the only 'mixing' which can happen is between
+	 * different fastfail types.  We can safely fail portions
+	 * which have all the failfast bits that the first one has -
+	 * the ones which are at least as eager to fail as the first
+	 * one.
+	 */
+	for (bio = rq->bio; bio; bio = bio->bi_next) {
+		if ((bio->bi_opf & ff) != ff)
+			break;
+		bytes += bio->bi_iter.bi_size;
+	}
+
+	/* this could lead to infinite loop */
+	BUG_ON(blk_rq_bytes(rq) && !bytes);
+	return bytes;
+}
+EXPORT_SYMBOL_GPL(blk_rq_err_bytes);
+
+void blk_account_io_completion(struct request *req, unsigned int bytes)
+{
+	if (blk_do_io_stat(req)) {
+		const int sgrp = op_stat_group(req_op(req));
+		struct hd_struct *part;
+		int cpu;
+
+		cpu = part_stat_lock();
+		part = req->part;
+		part_stat_add(cpu, part, sectors[sgrp], bytes >> 9);
+		part_stat_unlock();
+	}
+}
+
+void blk_account_io_done(struct request *req, u64 now)
+{
+	/*
+	 * Account IO completion.  flush_rq isn't accounted as a
+	 * normal IO on queueing nor completion.  Accounting the
+	 * containing request is enough.
+	 */
+	if (blk_do_io_stat(req) && !(req->rq_flags & RQF_FLUSH_SEQ)) {
+		const int sgrp = op_stat_group(req_op(req));
+		struct hd_struct *part;
+		int cpu;
+
+		cpu = part_stat_lock();
+		part = req->part;
+
+		part_stat_inc(cpu, part, ios[sgrp]);
+		part_stat_add(cpu, part, nsecs[sgrp], now - req->start_time_ns);
+		part_round_stats(req->q, cpu, part);
+		part_dec_in_flight(req->q, part, rq_data_dir(req));
+
+		hd_struct_put(part);
+		part_stat_unlock();
+	}
+}
+
+#ifdef CONFIG_PM
+/*
+ * Don't process normal requests when queue is suspended
+ * or in the process of suspending/resuming
+ */
+static bool blk_pm_allow_request(struct request *rq)
+{
+	switch (rq->q->rpm_status) {
+	case RPM_RESUMING:
+	case RPM_SUSPENDING:
+		return rq->rq_flags & RQF_PM;
+	case RPM_SUSPENDED:
+		return false;
+	default:
+		return true;
+	}
+}
+#else
+static bool blk_pm_allow_request(struct request *rq)
+{
+	return true;
+}
+#endif
+
+void blk_account_io_start(struct request *rq, bool new_io)
+{
+	struct hd_struct *part;
+	int rw = rq_data_dir(rq);
+	int cpu;
+
+	if (!blk_do_io_stat(rq))
+		return;
+
+	cpu = part_stat_lock();
+
+	if (!new_io) {
+		part = rq->part;
+		part_stat_inc(cpu, part, merges[rw]);
+	} else {
+		part = disk_map_sector_rcu(rq->rq_disk, blk_rq_pos(rq));
+		if (!hd_struct_try_get(part)) {
+			/*
+			 * The partition is already being removed,
+			 * the request will be accounted on the disk only
+			 *
+			 * We take a reference on disk->part0 although that
+			 * partition will never be deleted, so we can treat
+			 * it as any other partition.
+			 */
+			part = &rq->rq_disk->part0;
+			hd_struct_get(part);
+		}
+		part_round_stats(rq->q, cpu, part);
+		part_inc_in_flight(rq->q, part, rw);
+		rq->part = part;
+	}
+
+	part_stat_unlock();
+}
+
+static struct request *elv_next_request(struct request_queue *q)
+{
+	struct request *rq;
+	struct blk_flush_queue *fq = blk_get_flush_queue(q, NULL);
+
+	WARN_ON_ONCE(q->mq_ops);
+
+	while (1) {
+		list_for_each_entry(rq, &q->queue_head, queuelist) {
+			if (blk_pm_allow_request(rq))
+				return rq;
+
+			if (rq->rq_flags & RQF_SOFTBARRIER)
+				break;
+		}
+
+		/*
+		 * Flush request is running and flush request isn't queueable
+		 * in the drive, we can hold the queue till flush request is
+		 * finished. Even we don't do this, driver can't dispatch next
+		 * requests and will requeue them. And this can improve
+		 * throughput too. For example, we have request flush1, write1,
+		 * flush 2. flush1 is dispatched, then queue is hold, write1
+		 * isn't inserted to queue. After flush1 is finished, flush2
+		 * will be dispatched. Since disk cache is already clean,
+		 * flush2 will be finished very soon, so looks like flush2 is
+		 * folded to flush1.
+		 * Since the queue is hold, a flag is set to indicate the queue
+		 * should be restarted later. Please see flush_end_io() for
+		 * details.
+		 */
+		if (fq->flush_pending_idx != fq->flush_running_idx &&
+				!queue_flush_queueable(q)) {
+			fq->flush_queue_delayed = 1;
+			return NULL;
+		}
+		if (unlikely(blk_queue_bypass(q)) ||
+		    !q->elevator->type->ops.sq.elevator_dispatch_fn(q, 0))
+			return NULL;
+	}
+}
+
+/**
+ * blk_peek_request - peek at the top of a request queue
+ * @q: request queue to peek at
+ *
+ * Description:
+ *     Return the request at the top of @q.  The returned request
+ *     should be started using blk_start_request() before LLD starts
+ *     processing it.
+ *
+ * Return:
+ *     Pointer to the request at the top of @q if available.  Null
+ *     otherwise.
+ */
+struct request *blk_peek_request(struct request_queue *q)
+{
+	struct request *rq;
+	int ret;
+
+	lockdep_assert_held(q->queue_lock);
+	WARN_ON_ONCE(q->mq_ops);
+
+	while ((rq = elv_next_request(q)) != NULL) {
+		if (!(rq->rq_flags & RQF_STARTED)) {
+			/*
+			 * This is the first time the device driver
+			 * sees this request (possibly after
+			 * requeueing).  Notify IO scheduler.
+			 */
+			if (rq->rq_flags & RQF_SORTED)
+				elv_activate_rq(q, rq);
+
+			/*
+			 * just mark as started even if we don't start
+			 * it, a request that has been delayed should
+			 * not be passed by new incoming requests
+			 */
+			rq->rq_flags |= RQF_STARTED;
+			trace_block_rq_issue(q, rq);
+		}
+
+		if (!q->boundary_rq || q->boundary_rq == rq) {
+			q->end_sector = rq_end_sector(rq);
+			q->boundary_rq = NULL;
+		}
+
+		if (rq->rq_flags & RQF_DONTPREP)
+			break;
+
+		if (q->dma_drain_size && blk_rq_bytes(rq)) {
+			/*
+			 * make sure space for the drain appears we
+			 * know we can do this because max_hw_segments
+			 * has been adjusted to be one fewer than the
+			 * device can handle
+			 */
+			rq->nr_phys_segments++;
+		}
+
+		if (!q->prep_rq_fn)
+			break;
+
+		ret = q->prep_rq_fn(q, rq);
+		if (ret == BLKPREP_OK) {
+			break;
+		} else if (ret == BLKPREP_DEFER) {
+			/*
+			 * the request may have been (partially) prepped.
+			 * we need to keep this request in the front to
+			 * avoid resource deadlock.  RQF_STARTED will
+			 * prevent other fs requests from passing this one.
+			 */
+			if (q->dma_drain_size && blk_rq_bytes(rq) &&
+			    !(rq->rq_flags & RQF_DONTPREP)) {
+				/*
+				 * remove the space for the drain we added
+				 * so that we don't add it again
+				 */
+				--rq->nr_phys_segments;
+			}
+
+			rq = NULL;
+			break;
+		} else if (ret == BLKPREP_KILL || ret == BLKPREP_INVALID) {
+			rq->rq_flags |= RQF_QUIET;
+			/*
+			 * Mark this request as started so we don't trigger
+			 * any debug logic in the end I/O path.
+			 */
+			blk_start_request(rq);
+			__blk_end_request_all(rq, ret == BLKPREP_INVALID ?
+					BLK_STS_TARGET : BLK_STS_IOERR);
+		} else {
+			printk(KERN_ERR "%s: bad return=%d\n", __func__, ret);
+			break;
+		}
+	}
+
+	return rq;
+}
+EXPORT_SYMBOL(blk_peek_request);
+
+static void blk_dequeue_request(struct request *rq)
+{
+	struct request_queue *q = rq->q;
+
+	BUG_ON(list_empty(&rq->queuelist));
+	BUG_ON(ELV_ON_HASH(rq));
+
+	list_del_init(&rq->queuelist);
+
+	/*
+	 * the time frame between a request being removed from the lists
+	 * and to it is freed is accounted as io that is in progress at
+	 * the driver side.
+	 */
+	if (blk_account_rq(rq))
+		q->in_flight[rq_is_sync(rq)]++;
+}
+
+/**
+ * blk_start_request - start request processing on the driver
+ * @req: request to dequeue
+ *
+ * Description:
+ *     Dequeue @req and start timeout timer on it.  This hands off the
+ *     request to the driver.
+ */
+void blk_start_request(struct request *req)
+{
+	lockdep_assert_held(req->q->queue_lock);
+	WARN_ON_ONCE(req->q->mq_ops);
+
+	blk_dequeue_request(req);
+
+	if (test_bit(QUEUE_FLAG_STATS, &req->q->queue_flags)) {
+		req->io_start_time_ns = ktime_get_ns();
+#ifdef CONFIG_BLK_DEV_THROTTLING_LOW
+		req->throtl_size = blk_rq_sectors(req);
+#endif
+		req->rq_flags |= RQF_STATS;
+		rq_qos_issue(req->q, req);
+	}
+
+	BUG_ON(blk_rq_is_complete(req));
+	blk_add_timer(req);
+}
+EXPORT_SYMBOL(blk_start_request);
+
+/**
+ * blk_fetch_request - fetch a request from a request queue
+ * @q: request queue to fetch a request from
+ *
+ * Description:
+ *     Return the request at the top of @q.  The request is started on
+ *     return and LLD can start processing it immediately.
+ *
+ * Return:
+ *     Pointer to the request at the top of @q if available.  Null
+ *     otherwise.
+ */
+struct request *blk_fetch_request(struct request_queue *q)
+{
+	struct request *rq;
+
+	lockdep_assert_held(q->queue_lock);
+	WARN_ON_ONCE(q->mq_ops);
+
+	rq = blk_peek_request(q);
+	if (rq)
+		blk_start_request(rq);
+	return rq;
+}
+EXPORT_SYMBOL(blk_fetch_request);
+
+/*
+ * Steal bios from a request and add them to a bio list.
+ * The request must not have been partially completed before.
+ */
+void blk_steal_bios(struct bio_list *list, struct request *rq)
+{
+	if (rq->bio) {
+		if (list->tail)
+			list->tail->bi_next = rq->bio;
+		else
+			list->head = rq->bio;
+		list->tail = rq->biotail;
+
+		rq->bio = NULL;
+		rq->biotail = NULL;
+	}
+
+	rq->__data_len = 0;
+}
+EXPORT_SYMBOL_GPL(blk_steal_bios);
+
+/**
+ * blk_update_request - Special helper function for request stacking drivers
+ * @req:      the request being processed
+ * @error:    block status code
+ * @nr_bytes: number of bytes to complete @req
+ *
+ * Description:
+ *     Ends I/O on a number of bytes attached to @req, but doesn't complete
+ *     the request structure even if @req doesn't have leftover.
+ *     If @req has leftover, sets it up for the next range of segments.
+ *
+ *     This special helper function is only for request stacking drivers
+ *     (e.g. request-based dm) so that they can handle partial completion.
+ *     Actual device drivers should use blk_end_request instead.
+ *
+ *     Passing the result of blk_rq_bytes() as @nr_bytes guarantees
+ *     %false return from this function.
+ *
+ * Note:
+ *	The RQF_SPECIAL_PAYLOAD flag is ignored on purpose in both
+ *	blk_rq_bytes() and in blk_update_request().
+ *
+ * Return:
+ *     %false - this request doesn't have any more data
+ *     %true  - this request has more data
+ **/
+bool blk_update_request(struct request *req, blk_status_t error,
+		unsigned int nr_bytes)
+{
+	int total_bytes;
+
+	trace_block_rq_complete(req, blk_status_to_errno(error), nr_bytes);
+
+	if (!req->bio)
+		return false;
+
+	if (unlikely(error && !blk_rq_is_passthrough(req) &&
+		     !(req->rq_flags & RQF_QUIET)))
+		print_req_error(req, error);
+
+	blk_account_io_completion(req, nr_bytes);
+
+	total_bytes = 0;
+	while (req->bio) {
+		struct bio *bio = req->bio;
+		unsigned bio_bytes = min(bio->bi_iter.bi_size, nr_bytes);
+
+		if (bio_bytes == bio->bi_iter.bi_size)
+			req->bio = bio->bi_next;
+
+		/* Completion has already been traced */
+		bio_clear_flag(bio, BIO_TRACE_COMPLETION);
+		req_bio_endio(req, bio, bio_bytes, error);
+
+		total_bytes += bio_bytes;
+		nr_bytes -= bio_bytes;
+
+		if (!nr_bytes)
+			break;
+	}
+
+	/*
+	 * completely done
+	 */
+	if (!req->bio) {
+		/*
+		 * Reset counters so that the request stacking driver
+		 * can find how many bytes remain in the request
+		 * later.
+		 */
+		req->__data_len = 0;
+		return false;
+	}
+
+	req->__data_len -= total_bytes;
+
+	/* update sector only for requests with clear definition of sector */
+	if (!blk_rq_is_passthrough(req))
+		req->__sector += total_bytes >> 9;
+
+	/* mixed attributes always follow the first bio */
+	if (req->rq_flags & RQF_MIXED_MERGE) {
+		req->cmd_flags &= ~REQ_FAILFAST_MASK;
+		req->cmd_flags |= req->bio->bi_opf & REQ_FAILFAST_MASK;
+	}
+
+	if (!(req->rq_flags & RQF_SPECIAL_PAYLOAD)) {
+		/*
+		 * If total number of sectors is less than the first segment
+		 * size, something has gone terribly wrong.
+		 */
+		if (blk_rq_bytes(req) < blk_rq_cur_bytes(req)) {
+			blk_dump_rq_flags(req, "request botched");
+			req->__data_len = blk_rq_cur_bytes(req);
+		}
+
+		/* recalculate the number of segments */
+		blk_recalc_rq_segments(req);
+	}
+
+	return true;
+}
+EXPORT_SYMBOL_GPL(blk_update_request);
+
+static bool blk_update_bidi_request(struct request *rq, blk_status_t error,
+				    unsigned int nr_bytes,
+				    unsigned int bidi_bytes)
+{
+	if (blk_update_request(rq, error, nr_bytes))
+		return true;
+
+	/* Bidi request must be completed as a whole */
+	if (unlikely(blk_bidi_rq(rq)) &&
+	    blk_update_request(rq->next_rq, error, bidi_bytes))
+		return true;
+
+	if (blk_queue_add_random(rq->q))
+		add_disk_randomness(rq->rq_disk);
+
+	return false;
+}
+
+/**
+ * blk_unprep_request - unprepare a request
+ * @req:	the request
+ *
+ * This function makes a request ready for complete resubmission (or
+ * completion).  It happens only after all error handling is complete,
+ * so represents the appropriate moment to deallocate any resources
+ * that were allocated to the request in the prep_rq_fn.  The queue
+ * lock is held when calling this.
+ */
+void blk_unprep_request(struct request *req)
+{
+	struct request_queue *q = req->q;
+
+	req->rq_flags &= ~RQF_DONTPREP;
+	if (q->unprep_rq_fn)
+		q->unprep_rq_fn(q, req);
+}
+EXPORT_SYMBOL_GPL(blk_unprep_request);
+
+void blk_finish_request(struct request *req, blk_status_t error)
+{
+	struct request_queue *q = req->q;
+	u64 now = ktime_get_ns();
+
+	lockdep_assert_held(req->q->queue_lock);
+	WARN_ON_ONCE(q->mq_ops);
+
+	if (req->rq_flags & RQF_STATS)
+		blk_stat_add(req, now);
+
+	if (req->rq_flags & RQF_QUEUED)
+		blk_queue_end_tag(q, req);
+
+	BUG_ON(blk_queued_rq(req));
+
+	if (unlikely(laptop_mode) && !blk_rq_is_passthrough(req))
+		laptop_io_completion(req->q->backing_dev_info);
+
+	blk_delete_timer(req);
+
+	if (req->rq_flags & RQF_DONTPREP)
+		blk_unprep_request(req);
+
+	blk_account_io_done(req, now);
+
+	if (req->end_io) {
+		rq_qos_done(q, req);
+		req->end_io(req, error);
+	} else {
+		if (blk_bidi_rq(req))
+			__blk_put_request(req->next_rq->q, req->next_rq);
+
+		__blk_put_request(q, req);
+	}
+}
+EXPORT_SYMBOL(blk_finish_request);
+
+/**
+ * blk_end_bidi_request - Complete a bidi request
+ * @rq:         the request to complete
+ * @error:      block status code
+ * @nr_bytes:   number of bytes to complete @rq
+ * @bidi_bytes: number of bytes to complete @rq->next_rq
+ *
+ * Description:
+ *     Ends I/O on a number of bytes attached to @rq and @rq->next_rq.
+ *     Drivers that supports bidi can safely call this member for any
+ *     type of request, bidi or uni.  In the later case @bidi_bytes is
+ *     just ignored.
+ *
+ * Return:
+ *     %false - we are done with this request
+ *     %true  - still buffers pending for this request
+ **/
+static bool blk_end_bidi_request(struct request *rq, blk_status_t error,
+				 unsigned int nr_bytes, unsigned int bidi_bytes)
+{
+	struct request_queue *q = rq->q;
+	unsigned long flags;
+
+	WARN_ON_ONCE(q->mq_ops);
+
+	if (blk_update_bidi_request(rq, error, nr_bytes, bidi_bytes))
+		return true;
+
+	spin_lock_irqsave(q->queue_lock, flags);
+	blk_finish_request(rq, error);
+	spin_unlock_irqrestore(q->queue_lock, flags);
+
+	return false;
+}
+
+/**
+ * __blk_end_bidi_request - Complete a bidi request with queue lock held
+ * @rq:         the request to complete
+ * @error:      block status code
+ * @nr_bytes:   number of bytes to complete @rq
+ * @bidi_bytes: number of bytes to complete @rq->next_rq
+ *
+ * Description:
+ *     Identical to blk_end_bidi_request() except that queue lock is
+ *     assumed to be locked on entry and remains so on return.
+ *
+ * Return:
+ *     %false - we are done with this request
+ *     %true  - still buffers pending for this request
+ **/
+static bool __blk_end_bidi_request(struct request *rq, blk_status_t error,
+				   unsigned int nr_bytes, unsigned int bidi_bytes)
+{
+	lockdep_assert_held(rq->q->queue_lock);
+	WARN_ON_ONCE(rq->q->mq_ops);
+
+	if (blk_update_bidi_request(rq, error, nr_bytes, bidi_bytes))
+		return true;
+
+	blk_finish_request(rq, error);
+
+	return false;
+}
+
+/**
+ * blk_end_request - Helper function for drivers to complete the request.
+ * @rq:       the request being processed
+ * @error:    block status code
+ * @nr_bytes: number of bytes to complete
+ *
+ * Description:
+ *     Ends I/O on a number of bytes attached to @rq.
+ *     If @rq has leftover, sets it up for the next range of segments.
+ *
+ * Return:
+ *     %false - we are done with this request
+ *     %true  - still buffers pending for this request
+ **/
+bool blk_end_request(struct request *rq, blk_status_t error,
+		unsigned int nr_bytes)
+{
+	WARN_ON_ONCE(rq->q->mq_ops);
+	return blk_end_bidi_request(rq, error, nr_bytes, 0);
+}
+EXPORT_SYMBOL(blk_end_request);
+
+/**
+ * blk_end_request_all - Helper function for drives to finish the request.
+ * @rq: the request to finish
+ * @error: block status code
+ *
+ * Description:
+ *     Completely finish @rq.
+ */
+void blk_end_request_all(struct request *rq, blk_status_t error)
+{
+	bool pending;
+	unsigned int bidi_bytes = 0;
+
+	if (unlikely(blk_bidi_rq(rq)))
+		bidi_bytes = blk_rq_bytes(rq->next_rq);
+
+	pending = blk_end_bidi_request(rq, error, blk_rq_bytes(rq), bidi_bytes);
+	BUG_ON(pending);
+}
+EXPORT_SYMBOL(blk_end_request_all);
+
+/**
+ * __blk_end_request - Helper function for drivers to complete the request.
+ * @rq:       the request being processed
+ * @error:    block status code
+ * @nr_bytes: number of bytes to complete
+ *
+ * Description:
+ *     Must be called with queue lock held unlike blk_end_request().
+ *
+ * Return:
+ *     %false - we are done with this request
+ *     %true  - still buffers pending for this request
+ **/
+bool __blk_end_request(struct request *rq, blk_status_t error,
+		unsigned int nr_bytes)
+{
+	lockdep_assert_held(rq->q->queue_lock);
+	WARN_ON_ONCE(rq->q->mq_ops);
+
+	return __blk_end_bidi_request(rq, error, nr_bytes, 0);
+}
+EXPORT_SYMBOL(__blk_end_request);
+
+/**
+ * __blk_end_request_all - Helper function for drives to finish the request.
+ * @rq: the request to finish
+ * @error:    block status code
+ *
+ * Description:
+ *     Completely finish @rq.  Must be called with queue lock held.
+ */
+void __blk_end_request_all(struct request *rq, blk_status_t error)
+{
+	bool pending;
+	unsigned int bidi_bytes = 0;
+
+	lockdep_assert_held(rq->q->queue_lock);
+	WARN_ON_ONCE(rq->q->mq_ops);
+
+	if (unlikely(blk_bidi_rq(rq)))
+		bidi_bytes = blk_rq_bytes(rq->next_rq);
+
+	pending = __blk_end_bidi_request(rq, error, blk_rq_bytes(rq), bidi_bytes);
+	BUG_ON(pending);
+}
+EXPORT_SYMBOL(__blk_end_request_all);
+
+/**
+ * __blk_end_request_cur - Helper function to finish the current request chunk.
+ * @rq: the request to finish the current chunk for
+ * @error:    block status code
+ *
+ * Description:
+ *     Complete the current consecutively mapped chunk from @rq.  Must
+ *     be called with queue lock held.
+ *
+ * Return:
+ *     %false - we are done with this request
+ *     %true  - still buffers pending for this request
+ */
+bool __blk_end_request_cur(struct request *rq, blk_status_t error)
+{
+	return __blk_end_request(rq, error, blk_rq_cur_bytes(rq));
+}
+EXPORT_SYMBOL(__blk_end_request_cur);
+
+void blk_rq_bio_prep(struct request_queue *q, struct request *rq,
+		     struct bio *bio)
+{
+	if (bio_has_data(bio))
+		rq->nr_phys_segments = bio_phys_segments(q, bio);
+	else if (bio_op(bio) == REQ_OP_DISCARD)
+		rq->nr_phys_segments = 1;
+
+	rq->__data_len = bio->bi_iter.bi_size;
+	rq->bio = rq->biotail = bio;
+
+	if (bio->bi_disk)
+		rq->rq_disk = bio->bi_disk;
+}
+
+#if ARCH_IMPLEMENTS_FLUSH_DCACHE_PAGE
+/**
+ * rq_flush_dcache_pages - Helper function to flush all pages in a request
+ * @rq: the request to be flushed
+ *
+ * Description:
+ *     Flush all pages in @rq.
+ */
+void rq_flush_dcache_pages(struct request *rq)
+{
+	struct req_iterator iter;
+	struct bio_vec bvec;
+
+	rq_for_each_segment(bvec, rq, iter)
+		flush_dcache_page(bvec.bv_page);
+}
+EXPORT_SYMBOL_GPL(rq_flush_dcache_pages);
+#endif
+
+/**
+ * blk_lld_busy - Check if underlying low-level drivers of a device are busy
+ * @q : the queue of the device being checked
+ *
+ * Description:
+ *    Check if underlying low-level drivers of a device are busy.
+ *    If the drivers want to export their busy state, they must set own
+ *    exporting function using blk_queue_lld_busy() first.
+ *
+ *    Basically, this function is used only by request stacking drivers
+ *    to stop dispatching requests to underlying devices when underlying
+ *    devices are busy.  This behavior helps more I/O merging on the queue
+ *    of the request stacking driver and prevents I/O throughput regression
+ *    on burst I/O load.
+ *
+ * Return:
+ *    0 - Not busy (The request stacking driver should dispatch request)
+ *    1 - Busy (The request stacking driver should stop dispatching request)
+ */
+int blk_lld_busy(struct request_queue *q)
+{
+	if (q->lld_busy_fn)
+		return q->lld_busy_fn(q);
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(blk_lld_busy);
+
+/**
+ * blk_rq_unprep_clone - Helper function to free all bios in a cloned request
+ * @rq: the clone request to be cleaned up
+ *
+ * Description:
+ *     Free all bios in @rq for a cloned request.
+ */
+void blk_rq_unprep_clone(struct request *rq)
+{
+	struct bio *bio;
+
+	while ((bio = rq->bio) != NULL) {
+		rq->bio = bio->bi_next;
+
+		bio_put(bio);
+	}
+}
+EXPORT_SYMBOL_GPL(blk_rq_unprep_clone);
+
+/*
+ * Copy attributes of the original request to the clone request.
+ * The actual data parts (e.g. ->cmd, ->sense) are not copied.
+ */
+static void __blk_rq_prep_clone(struct request *dst, struct request *src)
+{
+	dst->cpu = src->cpu;
+	dst->__sector = blk_rq_pos(src);
+	dst->__data_len = blk_rq_bytes(src);
+	if (src->rq_flags & RQF_SPECIAL_PAYLOAD) {
+		dst->rq_flags |= RQF_SPECIAL_PAYLOAD;
+		dst->special_vec = src->special_vec;
+	}
+	dst->nr_phys_segments = src->nr_phys_segments;
+	dst->ioprio = src->ioprio;
+	dst->extra_len = src->extra_len;
+}
+
+/**
+ * blk_rq_prep_clone - Helper function to setup clone request
+ * @rq: the request to be setup
+ * @rq_src: original request to be cloned
+ * @bs: bio_set that bios for clone are allocated from
+ * @gfp_mask: memory allocation mask for bio
+ * @bio_ctr: setup function to be called for each clone bio.
+ *           Returns %0 for success, non %0 for failure.
+ * @data: private data to be passed to @bio_ctr
+ *
+ * Description:
+ *     Clones bios in @rq_src to @rq, and copies attributes of @rq_src to @rq.
+ *     The actual data parts of @rq_src (e.g. ->cmd, ->sense)
+ *     are not copied, and copying such parts is the caller's responsibility.
+ *     Also, pages which the original bios are pointing to are not copied
+ *     and the cloned bios just point same pages.
+ *     So cloned bios must be completed before original bios, which means
+ *     the caller must complete @rq before @rq_src.
+ */
+int blk_rq_prep_clone(struct request *rq, struct request *rq_src,
+		      struct bio_set *bs, gfp_t gfp_mask,
+		      int (*bio_ctr)(struct bio *, struct bio *, void *),
+		      void *data)
+{
+	struct bio *bio, *bio_src;
+
+	if (!bs)
+		bs = &fs_bio_set;
+
+	__rq_for_each_bio(bio_src, rq_src) {
+		bio = bio_clone_fast(bio_src, gfp_mask, bs);
+		if (!bio)
+			goto free_and_out;
+
+		if (bio_ctr && bio_ctr(bio, bio_src, data))
+			goto free_and_out;
+
+		if (rq->bio) {
+			rq->biotail->bi_next = bio;
+			rq->biotail = bio;
+		} else
+			rq->bio = rq->biotail = bio;
+	}
+
+	__blk_rq_prep_clone(rq, rq_src);
+
+	return 0;
+
+free_and_out:
+	if (bio)
+		bio_put(bio);
+	blk_rq_unprep_clone(rq);
+
+	return -ENOMEM;
+}
+EXPORT_SYMBOL_GPL(blk_rq_prep_clone);
+
+int kblockd_schedule_work(struct work_struct *work)
+{
+	return queue_work(kblockd_workqueue, work);
+}
+EXPORT_SYMBOL(kblockd_schedule_work);
+
+int kblockd_schedule_work_on(int cpu, struct work_struct *work)
+{
+	return queue_work_on(cpu, kblockd_workqueue, work);
+}
+EXPORT_SYMBOL(kblockd_schedule_work_on);
+
+int kblockd_mod_delayed_work_on(int cpu, struct delayed_work *dwork,
+				unsigned long delay)
+{
+	return mod_delayed_work_on(cpu, kblockd_workqueue, dwork, delay);
+}
+EXPORT_SYMBOL(kblockd_mod_delayed_work_on);
+
+/**
+ * blk_start_plug - initialize blk_plug and track it inside the task_struct
+ * @plug:	The &struct blk_plug that needs to be initialized
+ *
+ * Description:
+ *   Tracking blk_plug inside the task_struct will help with auto-flushing the
+ *   pending I/O should the task end up blocking between blk_start_plug() and
+ *   blk_finish_plug(). This is important from a performance perspective, but
+ *   also ensures that we don't deadlock. For instance, if the task is blocking
+ *   for a memory allocation, memory reclaim could end up wanting to free a
+ *   page belonging to that request that is currently residing in our private
+ *   plug. By flushing the pending I/O when the process goes to sleep, we avoid
+ *   this kind of deadlock.
+ */
+void blk_start_plug(struct blk_plug *plug)
+{
+	struct task_struct *tsk = current;
+
+	/*
+	 * If this is a nested plug, don't actually assign it.
+	 */
+	if (tsk->plug)
+		return;
+
+	INIT_LIST_HEAD(&plug->list);
+	INIT_LIST_HEAD(&plug->mq_list);
+	INIT_LIST_HEAD(&plug->cb_list);
+	/*
+	 * Store ordering should not be needed here, since a potential
+	 * preempt will imply a full memory barrier
+	 */
+	tsk->plug = plug;
+}
+EXPORT_SYMBOL(blk_start_plug);
+
+static int plug_rq_cmp(void *priv, struct list_head *a, struct list_head *b)
+{
+	struct request *rqa = container_of(a, struct request, queuelist);
+	struct request *rqb = container_of(b, struct request, queuelist);
+
+	return !(rqa->q < rqb->q ||
+		(rqa->q == rqb->q && blk_rq_pos(rqa) < blk_rq_pos(rqb)));
+}
+
+/*
+ * If 'from_schedule' is true, then postpone the dispatch of requests
+ * until a safe kblockd context. We due this to avoid accidental big
+ * additional stack usage in driver dispatch, in places where the originally
+ * plugger did not intend it.
+ */
+static void queue_unplugged(struct request_queue *q, unsigned int depth,
+			    bool from_schedule)
+	__releases(q->queue_lock)
+{
+	lockdep_assert_held(q->queue_lock);
+
+	trace_block_unplug(q, depth, !from_schedule);
+
+	if (from_schedule)
+		blk_run_queue_async(q);
+	else
+		__blk_run_queue(q);
+	spin_unlock_irq(q->queue_lock);
+}
+
+static void flush_plug_callbacks(struct blk_plug *plug, bool from_schedule)
+{
+	LIST_HEAD(callbacks);
+
+	while (!list_empty(&plug->cb_list)) {
+		list_splice_init(&plug->cb_list, &callbacks);
+
+		while (!list_empty(&callbacks)) {
+			struct blk_plug_cb *cb = list_first_entry(&callbacks,
+							  struct blk_plug_cb,
+							  list);
+			list_del(&cb->list);
+			cb->callback(cb, from_schedule);
+		}
+	}
+}
+
+struct blk_plug_cb *blk_check_plugged(blk_plug_cb_fn unplug, void *data,
+				      int size)
+{
+	struct blk_plug *plug = current->plug;
+	struct blk_plug_cb *cb;
+
+	if (!plug)
+		return NULL;
+
+	list_for_each_entry(cb, &plug->cb_list, list)
+		if (cb->callback == unplug && cb->data == data)
+			return cb;
+
+	/* Not currently on the callback list */
+	BUG_ON(size < sizeof(*cb));
+	cb = kzalloc(size, GFP_ATOMIC);
+	if (cb) {
+		cb->data = data;
+		cb->callback = unplug;
+		list_add(&cb->list, &plug->cb_list);
+	}
+	return cb;
+}
+EXPORT_SYMBOL(blk_check_plugged);
+
+void blk_flush_plug_list(struct blk_plug *plug, bool from_schedule)
+{
+	struct request_queue *q;
+	struct request *rq;
+	LIST_HEAD(list);
+	unsigned int depth;
+
+	flush_plug_callbacks(plug, from_schedule);
+
+	if (!list_empty(&plug->mq_list))
+		blk_mq_flush_plug_list(plug, from_schedule);
+
+	if (list_empty(&plug->list))
+		return;
+
+	list_splice_init(&plug->list, &list);
+
+	list_sort(NULL, &list, plug_rq_cmp);
+
+	q = NULL;
+	depth = 0;
+
+	while (!list_empty(&list)) {
+		rq = list_entry_rq(list.next);
+		list_del_init(&rq->queuelist);
+		BUG_ON(!rq->q);
+		if (rq->q != q) {
+			/*
+			 * This drops the queue lock
+			 */
+			if (q)
+				queue_unplugged(q, depth, from_schedule);
+			q = rq->q;
+			depth = 0;
+			spin_lock_irq(q->queue_lock);
+		}
+
+		/*
+		 * Short-circuit if @q is dead
+		 */
+		if (unlikely(blk_queue_dying(q))) {
+			__blk_end_request_all(rq, BLK_STS_IOERR);
+			continue;
+		}
+
+		/*
+		 * rq is already accounted, so use raw insert
+		 */
+		if (op_is_flush(rq->cmd_flags))
+			__elv_add_request(q, rq, ELEVATOR_INSERT_FLUSH);
+		else
+			__elv_add_request(q, rq, ELEVATOR_INSERT_SORT_MERGE);
+
+		depth++;
+	}
+
+	/*
+	 * This drops the queue lock
+	 */
+	if (q)
+		queue_unplugged(q, depth, from_schedule);
+}
+
+void blk_finish_plug(struct blk_plug *plug)
+{
+	if (plug != current->plug)
+		return;
+	blk_flush_plug_list(plug, false);
+
+	current->plug = NULL;
+}
+EXPORT_SYMBOL(blk_finish_plug);
+
+#ifdef CONFIG_PM
+/**
+ * blk_pm_runtime_init - Block layer runtime PM initialization routine
+ * @q: the queue of the device
+ * @dev: the device the queue belongs to
+ *
+ * Description:
+ *    Initialize runtime-PM-related fields for @q and start auto suspend for
+ *    @dev. Drivers that want to take advantage of request-based runtime PM
+ *    should call this function after @dev has been initialized, and its
+ *    request queue @q has been allocated, and runtime PM for it can not happen
+ *    yet(either due to disabled/forbidden or its usage_count > 0). In most
+ *    cases, driver should call this function before any I/O has taken place.
+ *
+ *    This function takes care of setting up using auto suspend for the device,
+ *    the autosuspend delay is set to -1 to make runtime suspend impossible
+ *    until an updated value is either set by user or by driver. Drivers do
+ *    not need to touch other autosuspend settings.
+ *
+ *    The block layer runtime PM is request based, so only works for drivers
+ *    that use request as their IO unit instead of those directly use bio's.
+ */
+void blk_pm_runtime_init(struct request_queue *q, struct device *dev)
+{
+	/* Don't enable runtime PM for blk-mq until it is ready */
+	if (q->mq_ops) {
+		pm_runtime_disable(dev);
+		return;
+	}
+
+	q->dev = dev;
+	q->rpm_status = RPM_ACTIVE;
+	pm_runtime_set_autosuspend_delay(q->dev, -1);
+	pm_runtime_use_autosuspend(q->dev);
+}
+EXPORT_SYMBOL(blk_pm_runtime_init);
+
+/**
+ * blk_pre_runtime_suspend - Pre runtime suspend check
+ * @q: the queue of the device
+ *
+ * Description:
+ *    This function will check if runtime suspend is allowed for the device
+ *    by examining if there are any requests pending in the queue. If there
+ *    are requests pending, the device can not be runtime suspended; otherwise,
+ *    the queue's status will be updated to SUSPENDING and the driver can
+ *    proceed to suspend the device.
+ *
+ *    For the not allowed case, we mark last busy for the device so that
+ *    runtime PM core will try to autosuspend it some time later.
+ *
+ *    This function should be called near the start of the device's
+ *    runtime_suspend callback.
+ *
+ * Return:
+ *    0		- OK to runtime suspend the device
+ *    -EBUSY	- Device should not be runtime suspended
+ */
+int blk_pre_runtime_suspend(struct request_queue *q)
+{
+	int ret = 0;
+
+	if (!q->dev)
+		return ret;
+
+	spin_lock_irq(q->queue_lock);
+	if (q->nr_pending) {
+		ret = -EBUSY;
+		pm_runtime_mark_last_busy(q->dev);
+	} else {
+		q->rpm_status = RPM_SUSPENDING;
+	}
+	spin_unlock_irq(q->queue_lock);
+	return ret;
+}
+EXPORT_SYMBOL(blk_pre_runtime_suspend);
+
+/**
+ * blk_post_runtime_suspend - Post runtime suspend processing
+ * @q: the queue of the device
+ * @err: return value of the device's runtime_suspend function
+ *
+ * Description:
+ *    Update the queue's runtime status according to the return value of the
+ *    device's runtime suspend function and mark last busy for the device so
+ *    that PM core will try to auto suspend the device at a later time.
+ *
+ *    This function should be called near the end of the device's
+ *    runtime_suspend callback.
+ */
+void blk_post_runtime_suspend(struct request_queue *q, int err)
+{
+	if (!q->dev)
+		return;
+
+	spin_lock_irq(q->queue_lock);
+	if (!err) {
+		q->rpm_status = RPM_SUSPENDED;
+	} else {
+		q->rpm_status = RPM_ACTIVE;
+		pm_runtime_mark_last_busy(q->dev);
+	}
+	spin_unlock_irq(q->queue_lock);
+}
+EXPORT_SYMBOL(blk_post_runtime_suspend);
+
+/**
+ * blk_pre_runtime_resume - Pre runtime resume processing
+ * @q: the queue of the device
+ *
+ * Description:
+ *    Update the queue's runtime status to RESUMING in preparation for the
+ *    runtime resume of the device.
+ *
+ *    This function should be called near the start of the device's
+ *    runtime_resume callback.
+ */
+void blk_pre_runtime_resume(struct request_queue *q)
+{
+	if (!q->dev)
+		return;
+
+	spin_lock_irq(q->queue_lock);
+	q->rpm_status = RPM_RESUMING;
+	spin_unlock_irq(q->queue_lock);
+}
+EXPORT_SYMBOL(blk_pre_runtime_resume);
+
+/**
+ * blk_post_runtime_resume - Post runtime resume processing
+ * @q: the queue of the device
+ * @err: return value of the device's runtime_resume function
+ *
+ * Description:
+ *    Update the queue's runtime status according to the return value of the
+ *    device's runtime_resume function. If it is successfully resumed, process
+ *    the requests that are queued into the device's queue when it is resuming
+ *    and then mark last busy and initiate autosuspend for it.
+ *
+ *    This function should be called near the end of the device's
+ *    runtime_resume callback.
+ */
+void blk_post_runtime_resume(struct request_queue *q, int err)
+{
+	if (!q->dev)
+		return;
+
+	spin_lock_irq(q->queue_lock);
+	if (!err) {
+		q->rpm_status = RPM_ACTIVE;
+		__blk_run_queue(q);
+		pm_runtime_mark_last_busy(q->dev);
+		pm_request_autosuspend(q->dev);
+	} else {
+		q->rpm_status = RPM_SUSPENDED;
+	}
+	spin_unlock_irq(q->queue_lock);
+}
+EXPORT_SYMBOL(blk_post_runtime_resume);
+
+/**
+ * blk_set_runtime_active - Force runtime status of the queue to be active
+ * @q: the queue of the device
+ *
+ * If the device is left runtime suspended during system suspend the resume
+ * hook typically resumes the device and corrects runtime status
+ * accordingly. However, that does not affect the queue runtime PM status
+ * which is still "suspended". This prevents processing requests from the
+ * queue.
+ *
+ * This function can be used in driver's resume hook to correct queue
+ * runtime PM status and re-enable peeking requests from the queue. It
+ * should be called before first request is added to the queue.
+ */
+void blk_set_runtime_active(struct request_queue *q)
+{
+	spin_lock_irq(q->queue_lock);
+	q->rpm_status = RPM_ACTIVE;
+	pm_runtime_mark_last_busy(q->dev);
+	pm_request_autosuspend(q->dev);
+	spin_unlock_irq(q->queue_lock);
+}
+EXPORT_SYMBOL(blk_set_runtime_active);
+#endif
+
+int __init blk_dev_init(void)
+{
+	BUILD_BUG_ON(REQ_OP_LAST >= (1 << REQ_OP_BITS));
+	BUILD_BUG_ON(REQ_OP_BITS + REQ_FLAG_BITS > 8 *
+			FIELD_SIZEOF(struct request, cmd_flags));
+	BUILD_BUG_ON(REQ_OP_BITS + REQ_FLAG_BITS > 8 *
+			FIELD_SIZEOF(struct bio, bi_opf));
+
+	/* used for unplugging and affects IO latency/throughput - HIGHPRI */
+	kblockd_workqueue = alloc_workqueue("kblockd",
+					    WQ_MEM_RECLAIM | WQ_HIGHPRI, 0);
+	if (!kblockd_workqueue)
+		panic("Failed to create kblockd\n");
+
+	request_cachep = kmem_cache_create("blkdev_requests",
+			sizeof(struct request), 0, SLAB_PANIC, NULL);
+
+	blk_requestq_cachep = kmem_cache_create("request_queue",
+			sizeof(struct request_queue), 0, SLAB_PANIC, NULL);
+
+#ifdef CONFIG_DEBUG_FS
+	blk_debugfs_root = debugfs_create_dir("block", NULL);
+#endif
+
+	return 0;
+}