[BLOCK] cfq-iosched: cfq forced dispatching fix

cfq forced dispatching might not return all requests on the queue.
This bug can hang elevator switchinig and corrupt request ordering
during flush sequence.

Signed-off-by: Tejun Heo <htejun@gmail.com>
Signed-off-by: Jens Axboe <axboe@suse.de>

1 files changed, 45 insertions, 9 deletions

diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
index ecacca9c877e..452538644bce 100644
--- a/block/cfq-iosched.c
+++ b/block/cfq-iosched.c
@@ -999,7 +999,7 @@ cfq_prio_to_maxrq(struct cfq_data *cfqd, struct cfq_queue *cfqq)
 /*
  * get next queue for service
  */
-static struct cfq_queue *cfq_select_queue(struct cfq_data *cfqd, int force)
+static struct cfq_queue *cfq_select_queue(struct cfq_data *cfqd)
 {
         unsigned long now = jiffies;
         struct cfq_queue *cfqq;
@@ -1023,7 +1023,7 @@ static struct cfq_queue *cfq_select_queue(struct cfq_data *cfqd, int force)
          */
         if (!RB_EMPTY(&cfqq->sort_list))
                 goto keep_queue;
-        else if (!force && cfq_cfqq_class_sync(cfqq) &&
+        else if (cfq_cfqq_class_sync(cfqq) &&
                  time_before(now, cfqq->slice_end)) {
                 if (cfq_arm_slice_timer(cfqd, cfqq))
                         return NULL;
@@ -1092,6 +1092,42 @@ __cfq_dispatch_requests(struct cfq_data *cfqd, struct cfq_queue *cfqq,
 }
 
 static int
+cfq_forced_dispatch_cfqqs(struct list_head *list)
+{
+        int dispatched = 0;
+        struct cfq_queue *cfqq, *next;
+        struct cfq_rq *crq;
+
+        list_for_each_entry_safe(cfqq, next, list, cfq_list) {
+                while ((crq = cfqq->next_crq)) {
+                        cfq_dispatch_insert(cfqq->cfqd->queue, crq);
+                        dispatched++;
+                }
+                BUG_ON(!list_empty(&cfqq->fifo));
+        }
+        return dispatched;
+}
+
+static int
+cfq_forced_dispatch(struct cfq_data *cfqd)
+{
+        int i, dispatched = 0;
+
+        for (i = 0; i < CFQ_PRIO_LISTS; i++)
+                dispatched += cfq_forced_dispatch_cfqqs(&cfqd->rr_list[i]);
+
+        dispatched += cfq_forced_dispatch_cfqqs(&cfqd->busy_rr);
+        dispatched += cfq_forced_dispatch_cfqqs(&cfqd->cur_rr);
+        dispatched += cfq_forced_dispatch_cfqqs(&cfqd->idle_rr);
+
+        cfq_slice_expired(cfqd, 0);
+
+        BUG_ON(cfqd->busy_queues);
+
+        return dispatched;
+}
+
+static int
 cfq_dispatch_requests(request_queue_t *q, int force)
 {
         struct cfq_data *cfqd = q->elevator->elevator_data;
@@ -1100,7 +1136,10 @@ cfq_dispatch_requests(request_queue_t *q, int force)
         if (!cfqd->busy_queues)
                 return 0;
 
-        cfqq = cfq_select_queue(cfqd, force);
+        if (unlikely(force))
+                return cfq_forced_dispatch(cfqd);
+
+        cfqq = cfq_select_queue(cfqd);
         if (cfqq) {
                 int max_dispatch;
 
@@ -1115,12 +1154,9 @@ cfq_dispatch_requests(request_queue_t *q, int force)
                 cfq_clear_cfqq_wait_request(cfqq);
                 del_timer(&cfqd->idle_slice_timer);
 
-                if (!force) {
-                        max_dispatch = cfqd->cfq_quantum;
-                        if (cfq_class_idle(cfqq))
-                                max_dispatch = 1;
-                } else
-                        max_dispatch = INT_MAX;
+                max_dispatch = cfqd->cfq_quantum;
+                if (cfq_class_idle(cfqq))
+                        max_dispatch = 1;
 
                 return __cfq_dispatch_requests(cfqd, cfqq, max_dispatch);
         }