block: introduce blk_flush_queue to drive flush machinery

This patch introduces 'struct blk_flush_queue' and puts all
flush machinery related fields into this structure, so that

	- flush implementation details aren't exposed to driver
	- it is easy to convert to per dispatch-queue flush machinery

This patch is basically a mechanical replacement.

Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Ming Lei <ming.lei@canonical.com>
Signed-off-by: Jens Axboe <axboe@fb.com>

4 files changed, 97 insertions, 48 deletions

diff --git a/block/blk-core.c b/block/blk-core.c
index 222fe84d6ac4..cfaca8ca6cc4 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -390,11 +390,13 @@ static void __blk_drain_queue(struct request_queue *q, bool drain_all)
                  * be drained.  Check all the queues and counters.
                  */
                 if (drain_all) {
+                        struct blk_flush_queue *fq = blk_get_flush_queue(q);
                         drain |= !list_empty(&q->queue_head);
                         for (i = 0; i < 2; i++) {
                                 drain |= q->nr_rqs[i];
                                 drain |= q->in_flight[i];
-                                drain |= !list_empty(&q->flush_queue[i]);
+                                if (fq)
+                                    drain |= !list_empty(&fq->flush_queue[i]);
                         }
                 }
 
diff --git a/block/blk-flush.c b/block/blk-flush.c
index caf44756d329..b01a86d6bf86 100644
--- a/block/blk-flush.c
+++ b/block/blk-flush.c
@@ -28,7 +28,7 @@
  *
  * 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
+ * fq->flush_queue[fq->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
@@ -155,7 +155,7 @@ static bool blk_flush_queue_rq(struct request *rq, bool add_front)
  * completion and trigger the next step.
  *
  * CONTEXT:
- * spin_lock_irq(q->queue_lock or q->mq_flush_lock)
+ * spin_lock_irq(q->queue_lock or fq->mq_flush_lock)
  *
  * RETURNS:
  * %true if requests were added to the dispatch queue, %false otherwise.
@@ -164,7 +164,8 @@ static bool blk_flush_complete_seq(struct request *rq, unsigned int seq,
                                    int error)
 {
         struct request_queue *q = rq->q;
-        struct list_head *pending = &q->flush_queue[q->flush_pending_idx];
+        struct blk_flush_queue *fq = blk_get_flush_queue(q);
+        struct list_head *pending = &fq->flush_queue[fq->flush_pending_idx];
         bool queued = false, kicked;
 
         BUG_ON(rq->flush.seq & seq);
@@ -180,12 +181,12 @@ static bool blk_flush_complete_seq(struct request *rq, unsigned int seq,
         case REQ_FSEQ_POSTFLUSH:
                 /* queue for flush */
                 if (list_empty(pending))
-                        q->flush_pending_since = jiffies;
+                        fq->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_move_tail(&rq->flush.list, &fq->flush_data_in_flight);
                 queued = blk_flush_queue_rq(rq, true);
                 break;
 
@@ -220,17 +221,18 @@ static void flush_end_io(struct request *flush_rq, int error)
         bool queued = false;
         struct request *rq, *n;
         unsigned long flags = 0;
+        struct blk_flush_queue *fq = blk_get_flush_queue(q);
 
         if (q->mq_ops) {
-                spin_lock_irqsave(&q->mq_flush_lock, flags);
+                spin_lock_irqsave(&fq->mq_flush_lock, flags);
                 flush_rq->tag = -1;
         }
 
-        running = &q->flush_queue[q->flush_running_idx];
-        BUG_ON(q->flush_pending_idx == q->flush_running_idx);
+        running = &fq->flush_queue[fq->flush_running_idx];
+        BUG_ON(fq->flush_pending_idx == fq->flush_running_idx);
 
         /* account completion of the flush request */
-        q->flush_running_idx ^= 1;
+        fq->flush_running_idx ^= 1;
 
         if (!q->mq_ops)
                 elv_completed_request(q, flush_rq);
@@ -254,13 +256,13 @@ static void flush_end_io(struct request *flush_rq, int error)
          * directly into request_fn may confuse the driver.  Always use
          * kblockd.
          */
-        if (queued || q->flush_queue_delayed) {
+        if (queued || fq->flush_queue_delayed) {
                 WARN_ON(q->mq_ops);
                 blk_run_queue_async(q);
         }
-        q->flush_queue_delayed = 0;
+        fq->flush_queue_delayed = 0;
         if (q->mq_ops)
-                spin_unlock_irqrestore(&q->mq_flush_lock, flags);
+                spin_unlock_irqrestore(&fq->mq_flush_lock, flags);
 }
 
 /**
@@ -271,33 +273,34 @@ static void flush_end_io(struct request *flush_rq, int error)
  * 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)
+ * spin_lock_irq(q->queue_lock or fq->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 blk_flush_queue *fq = blk_get_flush_queue(q);
+        struct list_head *pending = &fq->flush_queue[fq->flush_pending_idx];
         struct request *first_rq =
                 list_first_entry(pending, struct request, flush.list);
-        struct request *flush_rq = q->flush_rq;
+        struct request *flush_rq = fq->flush_rq;
 
         /* C1 described at the top of this file */
-        if (q->flush_pending_idx != q->flush_running_idx || list_empty(pending))
+        if (fq->flush_pending_idx != fq->flush_running_idx || list_empty(pending))
                 return false;
 
         /* C2 and C3 */
-        if (!list_empty(&q->flush_data_in_flight) &&
+        if (!list_empty(&fq->flush_data_in_flight) &&
             time_before(jiffies,
-                        q->flush_pending_since + FLUSH_PENDING_TIMEOUT))
+                        fq->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.
          */
-        q->flush_pending_idx ^= 1;
+        fq->flush_pending_idx ^= 1;
 
         blk_rq_init(q, flush_rq);
         if (q->mq_ops)
@@ -329,6 +332,7 @@ static void mq_flush_data_end_io(struct request *rq, int error)
         struct blk_mq_hw_ctx *hctx;
         struct blk_mq_ctx *ctx;
         unsigned long flags;
+        struct blk_flush_queue *fq = blk_get_flush_queue(q);
 
         ctx = rq->mq_ctx;
         hctx = q->mq_ops->map_queue(q, ctx->cpu);
@@ -337,10 +341,10 @@ static void mq_flush_data_end_io(struct request *rq, int error)
          * 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);
+        spin_lock_irqsave(&fq->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);
+        spin_unlock_irqrestore(&fq->mq_flush_lock, flags);
 }
 
 /**
@@ -408,11 +412,13 @@ void blk_insert_flush(struct request *rq)
         rq->cmd_flags |= REQ_FLUSH_SEQ;
         rq->flush.saved_end_io = rq->end_io; /* Usually NULL */
         if (q->mq_ops) {
+                struct blk_flush_queue *fq = blk_get_flush_queue(q);
+
                 rq->end_io = mq_flush_data_end_io;
 
-                spin_lock_irq(&q->mq_flush_lock);
+                spin_lock_irq(&fq->mq_flush_lock);
                 blk_flush_complete_seq(rq, REQ_FSEQ_ACTIONS & ~policy, 0);
-                spin_unlock_irq(&q->mq_flush_lock);
+                spin_unlock_irq(&fq->mq_flush_lock);
                 return;
         }
         rq->end_io = flush_data_end_io;
@@ -473,31 +479,52 @@ int blkdev_issue_flush(struct block_device *bdev, gfp_t gfp_mask,
 }
 EXPORT_SYMBOL(blkdev_issue_flush);
 
-static int blk_mq_init_flush(struct request_queue *q)
+static struct blk_flush_queue *blk_alloc_flush_queue(
+                struct request_queue *q)
 {
-        struct blk_mq_tag_set *set = q->tag_set;
+        struct blk_flush_queue *fq;
+        int rq_sz = sizeof(struct request);
 
-        spin_lock_init(&q->mq_flush_lock);
+        fq = kzalloc(sizeof(*fq), GFP_KERNEL);
+        if (!fq)
+                goto fail;
 
-        q->flush_rq = kzalloc(round_up(sizeof(struct request) +
-                                set->cmd_size, cache_line_size()),
-                                GFP_KERNEL);
-        if (!q->flush_rq)
-                return -ENOMEM;
-        return 0;
+        if (q->mq_ops) {
+                spin_lock_init(&fq->mq_flush_lock);
+                rq_sz = round_up(rq_sz + q->tag_set->cmd_size,
+                                cache_line_size());
+        }
+
+        fq->flush_rq = kzalloc(rq_sz, GFP_KERNEL);
+        if (!fq->flush_rq)
+                goto fail_rq;
+
+        INIT_LIST_HEAD(&fq->flush_queue[0]);
+        INIT_LIST_HEAD(&fq->flush_queue[1]);
+        INIT_LIST_HEAD(&fq->flush_data_in_flight);
+
+        return fq;
+
+ fail_rq:
+        kfree(fq);
+ fail:
+        return NULL;
 }
 
-int blk_init_flush(struct request_queue *q)
+static void blk_free_flush_queue(struct blk_flush_queue *fq)
 {
-        INIT_LIST_HEAD(&q->flush_queue[0]);
-        INIT_LIST_HEAD(&q->flush_queue[1]);
-        INIT_LIST_HEAD(&q->flush_data_in_flight);
+        /* bio based request queue hasn't flush queue */
+        if (!fq)
+                return;
 
-        if (q->mq_ops)
-                return blk_mq_init_flush(q);
+        kfree(fq->flush_rq);
+        kfree(fq);
+}
 
-        q->flush_rq = kzalloc(sizeof(struct request), GFP_KERNEL);
-        if (!q->flush_rq)
+int blk_init_flush(struct request_queue *q)
+{
+        q->fq = blk_alloc_flush_queue(q);
+        if (!q->fq)
                 return -ENOMEM;
 
         return 0;
@@ -505,5 +532,5 @@ int blk_init_flush(struct request_queue *q)
 
 void blk_exit_flush(struct request_queue *q)
 {
-        kfree(q->flush_rq);
+        blk_free_flush_queue(q->fq);
 }
diff --git a/block/blk-mq.c b/block/blk-mq.c
index 2758cdf2de94..d39e8a5eaeaa 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -508,20 +508,22 @@ void blk_mq_kick_requeue_list(struct request_queue *q)
 }
 EXPORT_SYMBOL(blk_mq_kick_requeue_list);
 
-static inline bool is_flush_request(struct request *rq, unsigned int tag)
+static inline bool is_flush_request(struct request *rq,
+                struct blk_flush_queue *fq, unsigned int tag)
 {
         return ((rq->cmd_flags & REQ_FLUSH_SEQ) &&
-                        rq->q->flush_rq->tag == tag);
+                        fq->flush_rq->tag == tag);
 }
 
 struct request *blk_mq_tag_to_rq(struct blk_mq_tags *tags, unsigned int tag)
 {
         struct request *rq = tags->rqs[tag];
+        struct blk_flush_queue *fq = blk_get_flush_queue(rq->q);
 
-        if (!is_flush_request(rq, tag))
+        if (!is_flush_request(rq, fq, tag))
                 return rq;
 
-        return rq->q->flush_rq;
+        return fq->flush_rq;
 }
 EXPORT_SYMBOL(blk_mq_tag_to_rq);
 
diff --git a/block/blk.h b/block/blk.h
index c6fa3d4c6a89..833c4ac6c4eb 100644
--- a/block/blk.h
+++ b/block/blk.h
@@ -12,11 +12,28 @@
 /* Max future timer expiry for timeouts */
 #define BLK_MAX_TIMEOUT         (5 * HZ)
 
+struct blk_flush_queue {
+        unsigned int            flush_queue_delayed:1;
+        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;
+        spinlock_t              mq_flush_lock;
+};
+
 extern struct kmem_cache *blk_requestq_cachep;
 extern struct kmem_cache *request_cachep;
 extern struct kobj_type blk_queue_ktype;
 extern struct ida blk_queue_ida;
 
+static inline struct blk_flush_queue *blk_get_flush_queue(
+                struct request_queue *q)
+{
+        return q->fq;
+}
+
 static inline void __blk_get_queue(struct request_queue *q)
 {
         kobject_get(&q->kobj);
@@ -89,6 +106,7 @@ void blk_insert_flush(struct request *rq);
 static inline struct request *__elv_next_request(struct request_queue *q)
 {
         struct request *rq;
+        struct blk_flush_queue *fq = blk_get_flush_queue(q);
 
         while (1) {
                 if (!list_empty(&q->queue_head)) {
@@ -111,9 +129,9 @@ static inline struct request *__elv_next_request(struct request_queue *q)
                  * should be restarted later. Please see flush_end_io() for
                  * details.
                  */
-                if (q->flush_pending_idx != q->flush_running_idx &&
+                if (fq->flush_pending_idx != fq->flush_running_idx &&
                                 !queue_flush_queueable(q)) {
-                        q->flush_queue_delayed = 1;
+                        fq->flush_queue_delayed = 1;
                         return NULL;
                 }
                 if (unlikely(blk_queue_bypass(q)) ||