dm: use md pending for in flight IO counting

This patch changes the counter for the number of in_flight I/Os
to md->pending from q->in_flight in preparation for a later patch.
No functional change.

Request-based dm used q->in_flight to count the number of in-flight
clones assuming the counter is always incremented for an in-flight
original request and original:clone is 1:1 relationship.
However, it this no longer true for barrier requests.
So use md->pending to count the number of in-flight clones.

Signed-off-by: Kiyoshi Ueda <k-ueda@ct.jp.nec.com>
Signed-off-by: Jun'ichi Nomura <j-nomura@ce.jp.nec.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>

1 files changed, 18 insertions, 28 deletions

diff --git a/drivers/md/dm.c b/drivers/md/dm.c
index 634b1daab2d4..01d741a0c079 100644
--- a/drivers/md/dm.c
+++ b/drivers/md/dm.c
@@ -727,23 +727,16 @@ static void end_clone_bio(struct bio *clone, int error)
  * the md may be freed in dm_put() at the end of this function.
  * Or do dm_get() before calling this function and dm_put() later.
  */
-static void rq_completed(struct mapped_device *md, int run_queue)
+static void rq_completed(struct mapped_device *md, int rw, int run_queue)
 {
-        int wakeup_waiters = 0;
-        struct request_queue *q = md->queue;
-        unsigned long flags;
-
-        spin_lock_irqsave(q->queue_lock, flags);
-        if (!queue_in_flight(q))
-                wakeup_waiters = 1;
-        spin_unlock_irqrestore(q->queue_lock, flags);
+        atomic_dec(&md->pending[rw]);
 
         /* nudge anyone waiting on suspend queue */
-        if (wakeup_waiters)
+        if (!md_in_flight(md))
                 wake_up(&md->wait);
 
         if (run_queue)
-                blk_run_queue(q);
+                blk_run_queue(md->queue);
 
         /*
          * dm_put() must be at the end of this function. See the comment above
@@ -774,6 +767,7 @@ static void dm_unprep_request(struct request *rq)
  */
 void dm_requeue_unmapped_request(struct request *clone)
 {
+        int rw = rq_data_dir(clone);
         struct dm_rq_target_io *tio = clone->end_io_data;
         struct mapped_device *md = tio->md;
         struct request *rq = tio->orig;
@@ -788,7 +782,7 @@ void dm_requeue_unmapped_request(struct request *clone)
         blk_requeue_request(q, rq);
         spin_unlock_irqrestore(q->queue_lock, flags);
 
-        rq_completed(md, 0);
+        rq_completed(md, rw, 0);
 }
 EXPORT_SYMBOL_GPL(dm_requeue_unmapped_request);
 
@@ -827,6 +821,7 @@ static void start_queue(struct request_queue *q)
  */
 static void dm_end_request(struct request *clone, int error)
 {
+        int rw = rq_data_dir(clone);
         struct dm_rq_target_io *tio = clone->end_io_data;
         struct mapped_device *md = tio->md;
         struct request *rq = tio->orig;
@@ -848,7 +843,7 @@ static void dm_end_request(struct request *clone, int error)
 
         blk_end_request_all(rq, error);
 
-        rq_completed(md, 1);
+        rq_completed(md, rw, 1);
 }
 
 /*
@@ -1541,12 +1536,13 @@ static void dm_request_fn(struct request_queue *q)
         struct mapped_device *md = q->queuedata;
         struct dm_table *map = dm_get_table(md);
         struct dm_target *ti;
-        struct request *rq;
+        struct request *rq, *clone;
 
         /*
-         * For suspend, check blk_queue_stopped() and don't increment
-         * the number of in-flight I/Os after the queue is stopped
-         * in dm_suspend().
+         * For suspend, check blk_queue_stopped() and increment
+         * ->pending within a single queue_lock not to increment the
+         * number of in-flight I/Os after the queue is stopped in
+         * dm_suspend().
          */
         while (!blk_queue_plugged(q) && !blk_queue_stopped(q)) {
                 rq = blk_peek_request(q);
@@ -1558,8 +1554,11 @@ static void dm_request_fn(struct request_queue *q)
                         goto plug_and_out;
 
                 blk_start_request(rq);
+                clone = rq->special;
+                atomic_inc(&md->pending[rq_data_dir(clone)]);
+
                 spin_unlock(q->queue_lock);
-                map_request(ti, rq->special, md);
+                map_request(ti, clone, md);
                 spin_lock_irq(q->queue_lock);
         }
 
@@ -2071,8 +2070,6 @@ static int dm_wait_for_completion(struct mapped_device *md, int interruptible)
 {
         int r = 0;
         DECLARE_WAITQUEUE(wait, current);
-        struct request_queue *q = md->queue;
-        unsigned long flags;
 
         dm_unplug_all(md->queue);
 
@@ -2082,14 +2079,7 @@ static int dm_wait_for_completion(struct mapped_device *md, int interruptible)
                 set_current_state(interruptible);
 
                 smp_mb();
-                if (dm_request_based(md)) {
-                        spin_lock_irqsave(q->queue_lock, flags);
-                        if (!queue_in_flight(q)) {
-                                spin_unlock_irqrestore(q->queue_lock, flags);
-                                break;
-                        }
-                        spin_unlock_irqrestore(q->queue_lock, flags);
-                } else if (!md_in_flight(md))
+                if (!md_in_flight(md))
                         break;
 
                 if (interruptible == TASK_INTERRUPTIBLE &&