6 files changed, 332 insertions, 156 deletions

diff --git a/block/blk-core.c b/block/blk-core.c
index 617bb9e40927..05746093b45e 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -134,8 +134,6 @@ EXPORT_SYMBOL(blk_rq_init);
 static void req_bio_endio(struct request *rq, struct bio *bio,
                           unsigned int nbytes, int error)
 {
-        struct request_queue *q = rq->q;
-
         if (error)
                 clear_bit(BIO_UPTODATE, &bio->bi_flags);
         else if (!test_bit(BIO_UPTODATE, &bio->bi_flags))
@@ -159,8 +157,6 @@ static void req_bio_endio(struct request *rq, struct bio *bio,
         /* don't actually finish bio if it's part of flush sequence */
         if (bio->bi_size == 0 && !(rq->cmd_flags & REQ_FLUSH_SEQ))
                 bio_endio(bio, error);
-        else if (error && !q->flush_err)
-                q->flush_err = error;
 }
 
 void blk_dump_rq_flags(struct request *rq, char *msg)
@@ -519,7 +515,9 @@ struct request_queue *blk_alloc_queue_node(gfp_t gfp_mask, int node_id)
         init_timer(&q->unplug_timer);
         setup_timer(&q->timeout, blk_rq_timed_out_timer, (unsigned long) q);
         INIT_LIST_HEAD(&q->timeout_list);
-        INIT_LIST_HEAD(&q->pending_flushes);
+        INIT_LIST_HEAD(&q->flush_queue[0]);
+        INIT_LIST_HEAD(&q->flush_queue[1]);
+        INIT_LIST_HEAD(&q->flush_data_in_flight);
         INIT_WORK(&q->unplug_work, blk_unplug_work);
 
         kobject_init(&q->kobj, &blk_queue_ktype);
@@ -1198,7 +1196,7 @@ static int __make_request(struct request_queue *q, struct bio *bio)
         spin_lock_irq(q->queue_lock);
 
         if (bio->bi_rw & (REQ_FLUSH | REQ_FUA)) {
-                where = ELEVATOR_INSERT_FRONT;
+                where = ELEVATOR_INSERT_FLUSH;
                 goto get_rq;
         }
 
diff --git a/block/blk-flush.c b/block/blk-flush.c
index 8592869bcbe7..a867e3f524f3 100644
--- a/block/blk-flush.c
+++ b/block/blk-flush.c
@@ -1,6 +1,69 @@
 /*
  * 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>
@@ -11,185 +74,290 @@
 
 /* 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),
+
+        REQ_FSEQ_ACTIONS        = REQ_FSEQ_PREFLUSH | REQ_FSEQ_DATA |
+                                  REQ_FSEQ_POSTFLUSH,
+
+        /*
+         * 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 *queue_next_fseq(struct request_queue *q);
+static bool blk_kick_flush(struct request_queue *q);
 
-unsigned blk_flush_cur_seq(struct request_queue *q)
+static unsigned int blk_flush_policy(unsigned int fflags, struct request *rq)
 {
-        if (!q->flush_seq)
-                return 0;
-        return 1 << ffz(q->flush_seq);
+        unsigned int policy = 0;
+
+        if (fflags & REQ_FLUSH) {
+                if (rq->cmd_flags & REQ_FLUSH)
+                        policy |= REQ_FSEQ_PREFLUSH;
+                if (blk_rq_sectors(rq))
+                        policy |= REQ_FSEQ_DATA;
+                if (!(fflags & REQ_FUA) && (rq->cmd_flags & REQ_FUA))
+                        policy |= REQ_FSEQ_POSTFLUSH;
+        }
+        return policy;
 }
 
-static struct request *blk_flush_complete_seq(struct request_queue *q,
-                                              unsigned seq, int error)
+static unsigned int blk_flush_cur_seq(struct request *rq)
 {
-        struct request *next_rq = NULL;
-
-        if (error && !q->flush_err)
-                q->flush_err = error;
-
-        BUG_ON(q->flush_seq & seq);
-        q->flush_seq |= seq;
-
-        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);
-                }
-        }
-        return next_rq;
+        return 1 << ffz(rq->flush.seq);
 }
 
-static void blk_flush_complete_seq_end_io(struct request_queue *q,
-                                          unsigned seq, int error)
+static void blk_flush_restore_request(struct request *rq)
 {
-        bool was_empty = elv_queue_empty(q);
-        struct request *next_rq;
-
-        next_rq = blk_flush_complete_seq(q, seq, error);
-
         /*
-         * Moving a request silently to empty queue_head may stall the
-         * queue.  Kick the queue in those cases.
+         * 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);
+        rq->bio = rq->biotail;
+
+        /* make @rq a normal request */
+        rq->cmd_flags &= ~REQ_FLUSH_SEQ;
+        rq->end_io = NULL;
 }
 
-static void pre_flush_end_io(struct request *rq, int error)
+/**
+ * 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)
+ *
+ * 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)
 {
-        elv_completed_request(rq->q, rq);
-        blk_flush_complete_seq_end_io(rq->q, QUEUE_FSEQ_PREFLUSH, error);
+        struct request_queue *q = rq->q;
+        struct list_head *pending = &q->flush_queue[q->flush_pending_idx];
+        bool queued = false;
+
+        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;
+
+        case REQ_FSEQ_DATA:
+                list_move_tail(&rq->flush.list, &q->flush_data_in_flight);
+                list_add(&rq->queuelist, &q->queue_head);
+                queued = true;
+                break;
+
+        case REQ_FSEQ_DONE:
+                /*
+                 * @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.
+                 */
+                BUG_ON(!list_empty(&rq->queuelist));
+                list_del_init(&rq->flush.list);
+                blk_flush_restore_request(rq);
+                __blk_end_request_all(rq, error);
+                break;
+
+        default:
+                BUG();
+        }
+
+        return blk_kick_flush(q) | queued;
 }
 
-static void flush_data_end_io(struct request *rq, int error)
+static void flush_end_io(struct request *flush_rq, int error)
 {
-        elv_completed_request(rq->q, rq);
-        blk_flush_complete_seq_end_io(rq->q, QUEUE_FSEQ_DATA, error);
+        struct request_queue *q = flush_rq->q;
+        struct list_head *running = &q->flush_queue[q->flush_running_idx];
+        bool was_empty = elv_queue_empty(q);
+        bool queued = false;
+        struct request *rq, *n;
+
+        BUG_ON(q->flush_pending_idx == q->flush_running_idx);
+
+        /* account completion of the flush request */
+        q->flush_running_idx ^= 1;
+        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);
+        }
+
+        /* after populating an empty queue, kick it to avoid stall */
+        if (queued && was_empty)
+                __blk_run_queue(q);
 }
 
-static void post_flush_end_io(struct request *rq, int error)
+/**
+ * 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)
+ *
+ * RETURNS:
+ * %true if flush was issued, %false otherwise.
+ */
+static bool blk_kick_flush(struct request_queue *q)
 {
-        elv_completed_request(rq->q, rq);
-        blk_flush_complete_seq_end_io(rq->q, QUEUE_FSEQ_POSTFLUSH, error);
+        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;
+
+        /*
+         * Issue flush and toggle pending_idx.  This makes pending_idx
+         * different from running_idx, which means flush is in flight.
+         */
+        blk_rq_init(q, &q->flush_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;
+
+        q->flush_pending_idx ^= 1;
+        elv_insert(q, &q->flush_rq, ELEVATOR_INSERT_FRONT);
+        return true;
 }
 
-static void init_flush_request(struct request *rq, struct gendisk *disk)
+static void flush_data_end_io(struct request *rq, int error)
 {
-        rq->cmd_type = REQ_TYPE_FS;
-        rq->cmd_flags = WRITE_FLUSH;
-        rq->rq_disk = disk;
+        struct request_queue *q = rq->q;
+        bool was_empty = elv_queue_empty(q);
+
+        /* after populating an empty queue, kick it to avoid stall */
+        if (blk_flush_complete_seq(rq, REQ_FSEQ_DATA, error) && was_empty)
+                __blk_run_queue(q);
 }
 
-static struct request *queue_next_fseq(struct request_queue *q)
+/**
+ * blk_insert_flush - insert a new FLUSH/FUA request
+ * @rq: request to insert
+ *
+ * To be called from elv_insert() for %ELEVATOR_INSERT_FLUSH insertions.
+ * @rq is being submitted.  Analyze what needs to be done and put it on the
+ * right queue.
+ *
+ * CONTEXT:
+ * spin_lock_irq(q->queue_lock)
+ */
+void blk_insert_flush(struct request *rq)
 {
-        struct request *orig_rq = q->orig_flush_rq;
-        struct request *rq = &q->flush_rq;
+        struct request_queue *q = rq->q;
+        unsigned int fflags = q->flush_flags;   /* may change, cache */
+        unsigned int policy = blk_flush_policy(fflags, rq);
 
-        blk_rq_init(q, rq);
+        BUG_ON(rq->end_io);
+        BUG_ON(!rq->bio || rq->bio != rq->biotail);
 
-        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;
-                break;
-        case QUEUE_FSEQ_DATA:
-                init_request_from_bio(rq, orig_rq->bio);
-                /*
-                 * 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->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;
-                break;
-        default:
-                BUG();
+        /*
+         * @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;
+
+        /*
+         * 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))) {
+                list_add(&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;
-        elv_insert(q, rq, ELEVATOR_INSERT_FRONT);
-        return rq;
+        rq->end_io = flush_data_end_io;
+
+        blk_flush_complete_seq(rq, REQ_FSEQ_ACTIONS & ~policy, 0);
 }
 
-struct request *blk_do_flush(struct request_queue *q, struct request *rq)
+/**
+ * blk_abort_flushes - @q is being aborted, abort flush requests
+ * @q: request_queue being aborted
+ *
+ * To be called from elv_abort_queue().  @q is being aborted.  Prepare all
+ * FLUSH/FUA requests for abortion.
+ *
+ * CONTEXT:
+ * spin_lock_irq(q->queue_lock)
+ */
+void blk_abort_flushes(struct request_queue *q)
 {
-        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 *rq, *n;
+        int i;
 
         /*
-         * 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.
+         * Requests in flight for data are already owned by the dispatch
+         * queue or the device driver.  Just restore for normal completion.
          */
-        if (blk_rq_sectors(rq) && !do_preflush && !do_postflush) {
-                rq->cmd_flags &= ~REQ_FLUSH;
-                if (!has_fua)
-                        rq->cmd_flags &= ~REQ_FUA;
-                return rq;
+        list_for_each_entry_safe(rq, n, &q->flush_data_in_flight, flush.list) {
+                list_del_init(&rq->flush.list);
+                blk_flush_restore_request(rq);
         }
 
         /*
-         * Sequenced flushes can't be processed in parallel.  If
-         * another one is already in progress, queue for later
-         * processing.
+         * We need to give away requests on flush queues.  Restore for
+         * normal completion and put them on the dispatch queue.
          */
-        if (q->flush_seq) {
-                list_move_tail(&rq->queuelist, &q->pending_flushes);
-                return NULL;
+        for (i = 0; i < ARRAY_SIZE(q->flush_queue); i++) {
+                list_for_each_entry_safe(rq, n, &q->flush_queue[i],
+                                         flush.list) {
+                        list_del_init(&rq->flush.list);
+                        blk_flush_restore_request(rq);
+                        list_add_tail(&rq->queuelist, &q->queue_head);
+                }
         }
-
-        /*
-         * Start a new flush sequence
-         */
-        q->flush_err = 0;
-        q->flush_seq |= QUEUE_FSEQ_STARTED;
-
-        /* 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 bio_end_flush(struct bio *bio, int err)
diff --git a/block/blk.h b/block/blk.h
index 9d2ee8f4d9af..284b500852bd 100644
--- a/block/blk.h
+++ b/block/blk.h
@@ -51,21 +51,17 @@ static inline void blk_clear_rq_complete(struct request *rq)
  */
 #define ELV_ON_HASH(rq)         (!hlist_unhashed(&(rq)->hash))
 
-struct request *blk_do_flush(struct request_queue *q, struct request *rq);
+void blk_insert_flush(struct request *rq);
+void blk_abort_flushes(struct request_queue *q);
 
 static inline struct request *__elv_next_request(struct request_queue *q)
 {
         struct request *rq;
 
         while (1) {
-                while (!list_empty(&q->queue_head)) {
+                if (!list_empty(&q->queue_head)) {
                         rq = list_entry_rq(q->queue_head.next);
-                        if (!(rq->cmd_flags & (REQ_FLUSH | REQ_FUA)) ||
-                            (rq->cmd_flags & REQ_FLUSH_SEQ))
-                                return rq;
-                        rq = blk_do_flush(q, rq);
-                        if (rq)
-                                return rq;
+                        return rq;
                 }
 
                 if (!q->elevator->ops->elevator_dispatch_fn(q, 0))
diff --git a/block/elevator.c b/block/elevator.c
index 2569512830d3..270e0972eb9f 100644
--- a/block/elevator.c
+++ b/block/elevator.c
@@ -673,6 +673,11 @@ void elv_insert(struct request_queue *q, struct request *rq, int where)
                 q->elevator->ops->elevator_add_req_fn(q, rq);
                 break;
 
+        case ELEVATOR_INSERT_FLUSH:
+                rq->cmd_flags |= REQ_SOFTBARRIER;
+                blk_insert_flush(rq);
+                break;
+
         default:
                 printk(KERN_ERR "%s: bad insertion point %d\n",
                        __func__, where);
@@ -785,6 +790,8 @@ void elv_abort_queue(struct request_queue *q)
 {
         struct request *rq;
 
+        blk_abort_flushes(q);
+
         while (!list_empty(&q->queue_head)) {
                 rq = list_entry_rq(q->queue_head.next);
                 rq->cmd_flags |= REQ_QUIET;
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index 36ab42c9bb99..6d7e9afd08c3 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -99,13 +99,18 @@ struct request {
         /*
          * The rb_node is only used inside the io scheduler, requests
          * are pruned when moved to the dispatch queue. So let the
-         * completion_data share space with the rb_node.
+         * flush fields share space with the rb_node.
          */
         union {
                 struct rb_node rb_node; /* sort/lookup */
-                void *completion_data;
+                struct {
+                        unsigned int                    seq;
+                        struct list_head                list;
+                } flush;
         };
 
+        void *completion_data;
+
         /*
          * Three pointers are available for the IO schedulers, if they need
          * more they have to dynamically allocate it.
@@ -362,11 +367,12 @@ struct request_queue
          * for flush operations
          */
         unsigned int            flush_flags;
-        unsigned int            flush_seq;
-        int                     flush_err;
+        unsigned int            flush_pending_idx:1;
+        unsigned int            flush_running_idx:1;
+        unsigned long           flush_pending_since;
+        struct list_head        flush_queue[2];
+        struct list_head        flush_data_in_flight;
         struct request          flush_rq;
-        struct request          *orig_flush_rq;
-        struct list_head        pending_flushes;
 
         struct mutex            sysfs_lock;
 
diff --git a/include/linux/elevator.h b/include/linux/elevator.h
index 4fd978e7eb83..86120c916fcc 100644
--- a/include/linux/elevator.h
+++ b/include/linux/elevator.h
@@ -167,6 +167,7 @@ extern struct request *elv_rb_find(struct rb_root *, sector_t);
 #define ELEVATOR_INSERT_BACK    2
 #define ELEVATOR_INSERT_SORT    3
 #define ELEVATOR_INSERT_REQUEUE 4
+#define ELEVATOR_INSERT_FLUSH   5
 
 /*
  * return values from elevator_may_queue_fn