1 files changed, 367 insertions, 151 deletions

diff --git a/block/blk-flush.c b/block/blk-flush.c
index b27d0208611..3cb5e9e7108 100644
--- a/block/blk-flush.c
+++ b/block/blk-flush.c
@@ -1,205 +1,424 @@
 /*
  * Functions to sequence FLUSH and FUA writes.
+ *
+ * Copyright (C) 2011		Max Planck Institute for Gravitational Physics
+ * Copyright (C) 2011		Tejun Heo <tj@kernel.org>
+ *
+ * This file is released under the GPLv2.
+ *
+ * REQ_{FLUSH|FUA} requests are decomposed to sequences consisted of three
+ * optional steps - PREFLUSH, DATA and POSTFLUSH - according to the request
+ * properties and hardware capability.
+ *
+ * If a request doesn't have data, only REQ_FLUSH makes sense, which
+ * indicates a simple flush request.  If there is data, REQ_FLUSH indicates
+ * that the device cache should be flushed before the data is executed, and
+ * REQ_FUA means that the data must be on non-volatile media on request
+ * completion.
+ *
+ * If the device doesn't have writeback cache, FLUSH and FUA don't make any
+ * difference.  The requests are either completed immediately if there's no
+ * data or executed as normal requests otherwise.
+ *
+ * If the device has writeback cache and supports FUA, REQ_FLUSH is
+ * translated to PREFLUSH but REQ_FUA is passed down directly with DATA.
+ *
+ * If the device has writeback cache and doesn't support FUA, REQ_FLUSH is
+ * translated to PREFLUSH and REQ_FUA to POSTFLUSH.
+ *
+ * The actual execution of flush is double buffered.  Whenever a request
+ * needs to execute PRE or POSTFLUSH, it queues at
+ * q->flush_queue[q->flush_pending_idx].  Once certain criteria are met, a
+ * flush is issued and the pending_idx is toggled.  When the flush
+ * completes, all the requests which were pending are proceeded to the next
+ * step.  This allows arbitrary merging of different types of FLUSH/FUA
+ * requests.
+ *
+ * Currently, the following conditions are used to determine when to issue
+ * flush.
+ *
+ * C1. At any given time, only one flush shall be in progress.  This makes
+ *     double buffering sufficient.
+ *
+ * C2. Flush is deferred if any request is executing DATA of its sequence.
+ *     This avoids issuing separate POSTFLUSHes for requests which shared
+ *     PREFLUSH.
+ *
+ * C3. The second condition is ignored if there is a request which has
+ *     waited longer than FLUSH_PENDING_TIMEOUT.  This is to avoid
+ *     starvation in the unlikely case where there are continuous stream of
+ *     FUA (without FLUSH) requests.
+ *
+ * For devices which support FUA, it isn't clear whether C2 (and thus C3)
+ * is beneficial.
+ *
+ * Note that a sequenced FLUSH/FUA request with DATA is completed twice.
+ * Once while executing DATA and again after the whole sequence is
+ * complete.  The first completion updates the contained bio but doesn't
+ * finish it so that the bio submitter is notified only after the whole
+ * sequence is complete.  This is implemented by testing REQ_FLUSH_SEQ in
+ * req_bio_endio().
+ *
+ * The above peculiarity requires that each FLUSH/FUA request has only one
+ * bio attached to it, which is guaranteed as they aren't allowed to be
+ * merged in the usual way.
  */
+
 #include <linux/kernel.h>
 #include <linux/module.h>
 #include <linux/bio.h>
 #include <linux/blkdev.h>
 #include <linux/gfp.h>
+#include <linux/blk-mq.h>
 
 #include "blk.h"
+#include "blk-mq.h"
 
 /* FLUSH/FUA sequences */
 enum {
-	QUEUE_FSEQ_STARTED	= (1 << 0), /* flushing in progress */
-	QUEUE_FSEQ_PREFLUSH	= (1 << 1), /* pre-flushing in progress */
-	QUEUE_FSEQ_DATA		= (1 << 2), /* data write in progress */
-	QUEUE_FSEQ_POSTFLUSH	= (1 << 3), /* post-flushing in progress */
-	QUEUE_FSEQ_DONE		= (1 << 4),
-};
+	REQ_FSEQ_PREFLUSH	= (1 << 0), /* pre-flushing in progress */
+	REQ_FSEQ_DATA		= (1 << 1), /* data write in progress */
+	REQ_FSEQ_POSTFLUSH	= (1 << 2), /* post-flushing in progress */
+	REQ_FSEQ_DONE		= (1 << 3),
 
-static struct request *queue_next_fseq(struct request_queue *q);
+	REQ_FSEQ_ACTIONS	= REQ_FSEQ_PREFLUSH | REQ_FSEQ_DATA |
+				  REQ_FSEQ_POSTFLUSH,
 
-unsigned blk_flush_cur_seq(struct request_queue *q)
-{
-	if (!q->flush_seq)
-		return 0;
-	return 1 << ffz(q->flush_seq);
-}
+	/*
+	 * If flush has been pending longer than the following timeout,
+	 * it's issued even if flush_data requests are still in flight.
+	 */
+	FLUSH_PENDING_TIMEOUT	= 5 * HZ,
+};
 
-static struct request *blk_flush_complete_seq(struct request_queue *q,
-					      unsigned seq, int error)
-{
-	struct request *next_rq = NULL;
+static bool blk_kick_flush(struct request_queue *q);
 
-	if (error && !q->flush_err)
-		q->flush_err = error;
+static unsigned int blk_flush_policy(unsigned int fflags, struct request *rq)
+{
+	unsigned int policy = 0;
 
-	BUG_ON(q->flush_seq & seq);
-	q->flush_seq |= seq;
+	if (blk_rq_sectors(rq))
+		policy |= REQ_FSEQ_DATA;
 
-	if (blk_flush_cur_seq(q) != QUEUE_FSEQ_DONE) {
-		/* not complete yet, queue the next flush sequence */
-		next_rq = queue_next_fseq(q);
-	} else {
-		/* complete this flush request */
-		__blk_end_request_all(q->orig_flush_rq, q->flush_err);
-		q->orig_flush_rq = NULL;
-		q->flush_seq = 0;
-
-		/* dispatch the next flush if there's one */
-		if (!list_empty(&q->pending_flushes)) {
-			next_rq = list_entry_rq(q->pending_flushes.next);
-			list_move(&next_rq->queuelist, &q->queue_head);
-		}
+	if (fflags & REQ_FLUSH) {
+		if (rq->cmd_flags & REQ_FLUSH)
+			policy |= REQ_FSEQ_PREFLUSH;
+		if (!(fflags & REQ_FUA) && (rq->cmd_flags & REQ_FUA))
+			policy |= REQ_FSEQ_POSTFLUSH;
 	}
-	return next_rq;
+	return policy;
 }
 
-static void blk_flush_complete_seq_end_io(struct request_queue *q,
-					  unsigned seq, int error)
+static unsigned int blk_flush_cur_seq(struct request *rq)
 {
-	bool was_empty = elv_queue_empty(q);
-	struct request *next_rq;
-
-	next_rq = blk_flush_complete_seq(q, seq, error);
+	return 1 << ffz(rq->flush.seq);
+}
 
+static void blk_flush_restore_request(struct request *rq)
+{
 	/*
-	 * Moving a request silently to empty queue_head may stall the
-	 * queue.  Kick the queue in those cases.  This function is called
-	 * from request completion path and calling directly into
-	 * request_fn may confuse the driver.  Always use kblockd.
+	 * After flush data completion, @rq->bio is %NULL but we need to
+	 * complete the bio again.  @rq->biotail is guaranteed to equal the
+	 * original @rq->bio.  Restore it.
 	 */
-	if (was_empty && next_rq)
-		__blk_run_queue(q, true);
-}
+	rq->bio = rq->biotail;
 
-static void pre_flush_end_io(struct request *rq, int error)
-{
-	elv_completed_request(rq->q, rq);
-	blk_flush_complete_seq_end_io(rq->q, QUEUE_FSEQ_PREFLUSH, error);
-}
+	/* make @rq a normal request */
+	rq->cmd_flags &= ~REQ_FLUSH_SEQ;
+	rq->end_io = rq->flush.saved_end_io;
 
-static void flush_data_end_io(struct request *rq, int error)
-{
-	elv_completed_request(rq->q, rq);
-	blk_flush_complete_seq_end_io(rq->q, QUEUE_FSEQ_DATA, error);
+	blk_clear_rq_complete(rq);
 }
 
-static void post_flush_end_io(struct request *rq, int error)
+static bool blk_flush_queue_rq(struct request *rq, bool add_front)
 {
-	elv_completed_request(rq->q, rq);
-	blk_flush_complete_seq_end_io(rq->q, QUEUE_FSEQ_POSTFLUSH, error);
-}
+	if (rq->q->mq_ops) {
+		struct request_queue *q = rq->q;
 
-static void init_flush_request(struct request *rq, struct gendisk *disk)
-{
-	rq->cmd_type = REQ_TYPE_FS;
-	rq->cmd_flags = WRITE_FLUSH;
-	rq->rq_disk = disk;
+		blk_mq_add_to_requeue_list(rq, add_front);
+		blk_mq_kick_requeue_list(q);
+		return false;
+	} else {
+		if (add_front)
+			list_add(&rq->queuelist, &rq->q->queue_head);
+		else
+			list_add_tail(&rq->queuelist, &rq->q->queue_head);
+		return true;
+	}
 }
 
-static struct request *queue_next_fseq(struct request_queue *q)
+/**
+ * blk_flush_complete_seq - complete flush sequence
+ * @rq: FLUSH/FUA request being sequenced
+ * @seq: sequences to complete (mask of %REQ_FSEQ_*, can be zero)
+ * @error: whether an error occurred
+ *
+ * @rq just completed @seq part of its flush sequence, record the
+ * completion and trigger the next step.
+ *
+ * CONTEXT:
+ * spin_lock_irq(q->queue_lock or q->mq_flush_lock)
+ *
+ * RETURNS:
+ * %true if requests were added to the dispatch queue, %false otherwise.
+ */
+static bool blk_flush_complete_seq(struct request *rq, unsigned int seq,
+				   int error)
 {
-	struct request *orig_rq = q->orig_flush_rq;
-	struct request *rq = &q->flush_rq;
-
-	blk_rq_init(q, rq);
+	struct request_queue *q = rq->q;
+	struct list_head *pending = &q->flush_queue[q->flush_pending_idx];
+	bool queued = false, kicked;
+
+	BUG_ON(rq->flush.seq & seq);
+	rq->flush.seq |= seq;
+
+	if (likely(!error))
+		seq = blk_flush_cur_seq(rq);
+	else
+		seq = REQ_FSEQ_DONE;
+
+	switch (seq) {
+	case REQ_FSEQ_PREFLUSH:
+	case REQ_FSEQ_POSTFLUSH:
+		/* queue for flush */
+		if (list_empty(pending))
+			q->flush_pending_since = jiffies;
+		list_move_tail(&rq->flush.list, pending);
+		break;
 
-	switch (blk_flush_cur_seq(q)) {
-	case QUEUE_FSEQ_PREFLUSH:
-		init_flush_request(rq, orig_rq->rq_disk);
-		rq->end_io = pre_flush_end_io;
+	case REQ_FSEQ_DATA:
+		list_move_tail(&rq->flush.list, &q->flush_data_in_flight);
+		queued = blk_flush_queue_rq(rq, true);
 		break;
-	case QUEUE_FSEQ_DATA:
-		init_request_from_bio(rq, orig_rq->bio);
+
+	case REQ_FSEQ_DONE:
 		/*
-		 * orig_rq->rq_disk may be different from
-		 * bio->bi_bdev->bd_disk if orig_rq got here through
-		 * remapping drivers.  Make sure rq->rq_disk points
-		 * to the same one as orig_rq.
+		 * @rq was previously adjusted by blk_flush_issue() for
+		 * flush sequencing and may already have gone through the
+		 * flush data request completion path.  Restore @rq for
+		 * normal completion and end it.
 		 */
-		rq->rq_disk = orig_rq->rq_disk;
-		rq->cmd_flags &= ~(REQ_FLUSH | REQ_FUA);
-		rq->cmd_flags |= orig_rq->cmd_flags & (REQ_FLUSH | REQ_FUA);
-		rq->end_io = flush_data_end_io;
-		break;
-	case QUEUE_FSEQ_POSTFLUSH:
-		init_flush_request(rq, orig_rq->rq_disk);
-		rq->end_io = post_flush_end_io;
+		BUG_ON(!list_empty(&rq->queuelist));
+		list_del_init(&rq->flush.list);
+		blk_flush_restore_request(rq);
+		if (q->mq_ops)
+			blk_mq_end_io(rq, error);
+		else
+			__blk_end_request_all(rq, error);
 		break;
+
 	default:
 		BUG();
 	}
 
-	elv_insert(q, rq, ELEVATOR_INSERT_REQUEUE);
-	return rq;
+	kicked = blk_kick_flush(q);
+	return kicked | queued;
 }
 
-struct request *blk_do_flush(struct request_queue *q, struct request *rq)
+static void flush_end_io(struct request *flush_rq, int error)
 {
-	unsigned int fflags = q->flush_flags; /* may change, cache it */
-	bool has_flush = fflags & REQ_FLUSH, has_fua = fflags & REQ_FUA;
-	bool do_preflush = has_flush && (rq->cmd_flags & REQ_FLUSH);
-	bool do_postflush = has_flush && !has_fua && (rq->cmd_flags & REQ_FUA);
-	unsigned skip = 0;
+	struct request_queue *q = flush_rq->q;
+	struct list_head *running;
+	bool queued = false;
+	struct request *rq, *n;
+	unsigned long flags = 0;
+
+	if (q->mq_ops) {
+		spin_lock_irqsave(&q->mq_flush_lock, flags);
+		q->flush_rq->tag = -1;
+	}
+
+	running = &q->flush_queue[q->flush_running_idx];
+	BUG_ON(q->flush_pending_idx == q->flush_running_idx);
+
+	/* account completion of the flush request */
+	q->flush_running_idx ^= 1;
+
+	if (!q->mq_ops)
+		elv_completed_request(q, flush_rq);
+
+	/* and push the waiting requests to the next stage */
+	list_for_each_entry_safe(rq, n, running, flush.list) {
+		unsigned int seq = blk_flush_cur_seq(rq);
+
+		BUG_ON(seq != REQ_FSEQ_PREFLUSH && seq != REQ_FSEQ_POSTFLUSH);
+		queued |= blk_flush_complete_seq(rq, seq, error);
+	}
 
 	/*
-	 * Special case.  If there's data but flush is not necessary,
-	 * the request can be issued directly.
-	 *
-	 * Flush w/o data should be able to be issued directly too but
-	 * currently some drivers assume that rq->bio contains
-	 * non-zero data if it isn't NULL and empty FLUSH requests
-	 * getting here usually have bio's without data.
+	 * Kick the queue to avoid stall for two cases:
+	 * 1. Moving a request silently to empty queue_head may stall the
+	 * queue.
+	 * 2. When flush request is running in non-queueable queue, the
+	 * queue is hold. Restart the queue after flush request is finished
+	 * to avoid stall.
+	 * This function is called from request completion path and calling
+	 * directly into request_fn may confuse the driver.  Always use
+	 * kblockd.
 	 */
-	if (blk_rq_sectors(rq) && !do_preflush && !do_postflush) {
-		rq->cmd_flags &= ~REQ_FLUSH;
-		if (!has_fua)
-			rq->cmd_flags &= ~REQ_FUA;
-		return rq;
+	if (queued || q->flush_queue_delayed) {
+		WARN_ON(q->mq_ops);
+		blk_run_queue_async(q);
 	}
+	q->flush_queue_delayed = 0;
+	if (q->mq_ops)
+		spin_unlock_irqrestore(&q->mq_flush_lock, flags);
+}
+
+/**
+ * blk_kick_flush - consider issuing flush request
+ * @q: request_queue being kicked
+ *
+ * Flush related states of @q have changed, consider issuing flush request.
+ * Please read the comment at the top of this file for more info.
+ *
+ * CONTEXT:
+ * spin_lock_irq(q->queue_lock or q->mq_flush_lock)
+ *
+ * RETURNS:
+ * %true if flush was issued, %false otherwise.
+ */
+static bool blk_kick_flush(struct request_queue *q)
+{
+	struct list_head *pending = &q->flush_queue[q->flush_pending_idx];
+	struct request *first_rq =
+		list_first_entry(pending, struct request, flush.list);
+
+	/* C1 described at the top of this file */
+	if (q->flush_pending_idx != q->flush_running_idx || list_empty(pending))
+		return false;
+
+	/* C2 and C3 */
+	if (!list_empty(&q->flush_data_in_flight) &&
+	    time_before(jiffies,
+			q->flush_pending_since + FLUSH_PENDING_TIMEOUT))
+		return false;
 
 	/*
-	 * Sequenced flushes can't be processed in parallel.  If
-	 * another one is already in progress, queue for later
-	 * processing.
+	 * Issue flush and toggle pending_idx.  This makes pending_idx
+	 * different from running_idx, which means flush is in flight.
 	 */
-	if (q->flush_seq) {
-		list_move_tail(&rq->queuelist, &q->pending_flushes);
-		return NULL;
-	}
+	q->flush_pending_idx ^= 1;
+
+	blk_rq_init(q, q->flush_rq);
+	if (q->mq_ops)
+		blk_mq_clone_flush_request(q->flush_rq, first_rq);
+
+	q->flush_rq->cmd_type = REQ_TYPE_FS;
+	q->flush_rq->cmd_flags = WRITE_FLUSH | REQ_FLUSH_SEQ;
+	q->flush_rq->rq_disk = first_rq->rq_disk;
+	q->flush_rq->end_io = flush_end_io;
+
+	return blk_flush_queue_rq(q->flush_rq, false);
+}
+
+static void flush_data_end_io(struct request *rq, int error)
+{
+	struct request_queue *q = rq->q;
 
 	/*
-	 * Start a new flush sequence
+	 * After populating an empty queue, kick it to avoid stall.  Read
+	 * the comment in flush_end_io().
 	 */
-	q->flush_err = 0;
-	q->flush_seq |= QUEUE_FSEQ_STARTED;
+	if (blk_flush_complete_seq(rq, REQ_FSEQ_DATA, error))
+		blk_run_queue_async(q);
+}
 
-	/* adjust FLUSH/FUA of the original request and stash it away */
-	rq->cmd_flags &= ~REQ_FLUSH;
-	if (!has_fua)
-		rq->cmd_flags &= ~REQ_FUA;
-	blk_dequeue_request(rq);
-	q->orig_flush_rq = rq;
-
-	/* skip unneded sequences and return the first one */
-	if (!do_preflush)
-		skip |= QUEUE_FSEQ_PREFLUSH;
-	if (!blk_rq_sectors(rq))
-		skip |= QUEUE_FSEQ_DATA;
-	if (!do_postflush)
-		skip |= QUEUE_FSEQ_POSTFLUSH;
-	return blk_flush_complete_seq(q, skip, 0);
+static void mq_flush_data_end_io(struct request *rq, int error)
+{
+	struct request_queue *q = rq->q;
+	struct blk_mq_hw_ctx *hctx;
+	struct blk_mq_ctx *ctx;
+	unsigned long flags;
+
+	ctx = rq->mq_ctx;
+	hctx = q->mq_ops->map_queue(q, ctx->cpu);
+
+	/*
+	 * After populating an empty queue, kick it to avoid stall.  Read
+	 * the comment in flush_end_io().
+	 */
+	spin_lock_irqsave(&q->mq_flush_lock, flags);
+	if (blk_flush_complete_seq(rq, REQ_FSEQ_DATA, error))
+		blk_mq_run_hw_queue(hctx, true);
+	spin_unlock_irqrestore(&q->mq_flush_lock, flags);
 }
 
-static void bio_end_flush(struct bio *bio, int err)
+/**
+ * blk_insert_flush - insert a new FLUSH/FUA request
+ * @rq: request to insert
+ *
+ * To be called from __elv_add_request() for %ELEVATOR_INSERT_FLUSH insertions.
+ * or __blk_mq_run_hw_queue() to dispatch request.
+ * @rq is being submitted.  Analyze what needs to be done and put it on the
+ * right queue.
+ *
+ * CONTEXT:
+ * spin_lock_irq(q->queue_lock) in !mq case
+ */
+void blk_insert_flush(struct request *rq)
 {
-	if (err)
-		clear_bit(BIO_UPTODATE, &bio->bi_flags);
-	if (bio->bi_private)
-		complete(bio->bi_private);
-	bio_put(bio);
+	struct request_queue *q = rq->q;
+	unsigned int fflags = q->flush_flags;	/* may change, cache */
+	unsigned int policy = blk_flush_policy(fflags, rq);
+
+	/*
+	 * @policy now records what operations need to be done.  Adjust
+	 * REQ_FLUSH and FUA for the driver.
+	 */
+	rq->cmd_flags &= ~REQ_FLUSH;
+	if (!(fflags & REQ_FUA))
+		rq->cmd_flags &= ~REQ_FUA;
+
+	/*
+	 * An empty flush handed down from a stacking driver may
+	 * translate into nothing if the underlying device does not
+	 * advertise a write-back cache.  In this case, simply
+	 * complete the request.
+	 */
+	if (!policy) {
+		if (q->mq_ops)
+			blk_mq_end_io(rq, 0);
+		else
+			__blk_end_bidi_request(rq, 0, 0, 0);
+		return;
+	}
+
+	BUG_ON(rq->bio != rq->biotail); /*assumes zero or single bio rq */
+
+	/*
+	 * If there's data but flush is not necessary, the request can be
+	 * processed directly without going through flush machinery.  Queue
+	 * for normal execution.
+	 */
+	if ((policy & REQ_FSEQ_DATA) &&
+	    !(policy & (REQ_FSEQ_PREFLUSH | REQ_FSEQ_POSTFLUSH))) {
+		if (q->mq_ops) {
+			blk_mq_insert_request(rq, false, false, true);
+		} else
+			list_add_tail(&rq->queuelist, &q->queue_head);
+		return;
+	}
+
+	/*
+	 * @rq should go through flush machinery.  Mark it part of flush
+	 * sequence and submit for further processing.
+	 */
+	memset(&rq->flush, 0, sizeof(rq->flush));
+	INIT_LIST_HEAD(&rq->flush.list);
+	rq->cmd_flags |= REQ_FLUSH_SEQ;
+	rq->flush.saved_end_io = rq->end_io; /* Usually NULL */
+	if (q->mq_ops) {
+		rq->end_io = mq_flush_data_end_io;
+
+		spin_lock_irq(&q->mq_flush_lock);
+		blk_flush_complete_seq(rq, REQ_FSEQ_ACTIONS & ~policy, 0);
+		spin_unlock_irq(&q->mq_flush_lock);
+		return;
+	}
+	rq->end_io = flush_data_end_io;
+
+	blk_flush_complete_seq(rq, REQ_FSEQ_ACTIONS & ~policy, 0);
 }
 
 /**
@@ -217,7 +436,6 @@ static void bio_end_flush(struct bio *bio, int err)
 int blkdev_issue_flush(struct block_device *bdev, gfp_t gfp_mask,
 		sector_t *error_sector)
 {
-	DECLARE_COMPLETION_ONSTACK(wait);
 	struct request_queue *q;
 	struct bio *bio;
 	int ret = 0;
@@ -239,13 +457,9 @@ int blkdev_issue_flush(struct block_device *bdev, gfp_t gfp_mask,
 		return -ENXIO;
 
 	bio = bio_alloc(gfp_mask, 0);
-	bio->bi_end_io = bio_end_flush;
 	bio->bi_bdev = bdev;
-	bio->bi_private = &wait;
 
-	bio_get(bio);
-	submit_bio(WRITE_FLUSH, bio);
-	wait_for_completion(&wait);
+	ret = submit_bio_wait(WRITE_FLUSH, bio);
 
 	/*
 	 * The driver must store the error location in ->bi_sector, if
@@ -253,12 +467,14 @@ int blkdev_issue_flush(struct block_device *bdev, gfp_t gfp_mask,
 	 * copied from blk_rq_pos(rq).
 	 */
 	if (error_sector)
-               *error_sector = bio->bi_sector;
-
-	if (!bio_flagged(bio, BIO_UPTODATE))
-		ret = -EIO;
+		*error_sector = bio->bi_iter.bi_sector;
 
 	bio_put(bio);
 	return ret;
 }
 EXPORT_SYMBOL(blkdev_issue_flush);
+
+void blk_mq_init_flush(struct request_queue *q)
+{
+	spin_lock_init(&q->mq_flush_lock);
+}