[PATCH] cfq-iosched: slice expiry fixups

During testing of SLES10, we encountered a hang in the CFQ io scheduler.
Turns out the deferred slice expiry logic is buggy, so remove that for
now.  We could be left with an idle queue that would never wake up.  So
kill that logic, always expire immediately.  Also fix a potential timer
race condition.

Patch looks bigger than it is, because it moves a function.
Signed-off-by: Jens Axboe <axboe@suse.de>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

block/cfq-iosched.c

@@ -239,7 +239,6 @@ enum cfqq_state_flags {
 	CFQ_CFQQ_FLAG_fifo_expire,
 	CFQ_CFQQ_FLAG_idle_window,
 	CFQ_CFQQ_FLAG_prio_changed,
-	CFQ_CFQQ_FLAG_expired,
 };
 
 #define CFQ_CFQQ_FNS(name)						\
@@ -264,7 +263,6 @@ CFQ_CFQQ_FNS(must_dispatch);
 CFQ_CFQQ_FNS(fifo_expire);
 CFQ_CFQQ_FNS(idle_window);
 CFQ_CFQQ_FNS(prio_changed);
-CFQ_CFQQ_FNS(expired);
 #undef CFQ_CFQQ_FNS
 
 enum cfq_rq_state_flags {
@@ -336,7 +334,7 @@ static struct request *cfq_find_rq_hash(struct cfq_data *cfqd, sector_t offset)
  */
 static inline void cfq_schedule_dispatch(struct cfq_data *cfqd)
 {
-	if (!cfqd->rq_in_driver && cfqd->busy_queues)
+	if (cfqd->busy_queues)
 		kblockd_schedule_work(&cfqd->unplug_work);
 }
 
@@ -736,12 +734,62 @@ __cfq_set_active_queue(struct cfq_data *cfqd, struct cfq_queue *cfqq)
 		cfqq->slice_left = 0;
 		cfq_clear_cfqq_must_alloc_slice(cfqq);
 		cfq_clear_cfqq_fifo_expire(cfqq);
-		cfq_clear_cfqq_expired(cfqq);
 	}
 
 	cfqd->active_queue = cfqq;
 }
 
+/*
+ * current cfqq expired its slice (or was too idle), select new one
+ */
+static void
+__cfq_slice_expired(struct cfq_data *cfqd, struct cfq_queue *cfqq,
+		    int preempted)
+{
+	unsigned long now = jiffies;
+
+	if (cfq_cfqq_wait_request(cfqq))
+		del_timer(&cfqd->idle_slice_timer);
+
+	if (!preempted && !cfq_cfqq_dispatched(cfqq)) {
+		cfqq->service_last = now;
+		cfq_schedule_dispatch(cfqd);
+	}
+
+	cfq_clear_cfqq_must_dispatch(cfqq);
+	cfq_clear_cfqq_wait_request(cfqq);
+
+	/*
+	 * store what was left of this slice, if the queue idled out
+	 * or was preempted
+	 */
+	if (time_after(cfqq->slice_end, now))
+		cfqq->slice_left = cfqq->slice_end - now;
+	else
+		cfqq->slice_left = 0;
+
+	if (cfq_cfqq_on_rr(cfqq))
+		cfq_resort_rr_list(cfqq, preempted);
+
+	if (cfqq == cfqd->active_queue)
+		cfqd->active_queue = NULL;
+
+	if (cfqd->active_cic) {
+		put_io_context(cfqd->active_cic->ioc);
+		cfqd->active_cic = NULL;
+	}
+
+	cfqd->dispatch_slice = 0;
+}
+
+static inline void cfq_slice_expired(struct cfq_data *cfqd, int preempted)
+{
+	struct cfq_queue *cfqq = cfqd->active_queue;
+
+	if (cfqq)
+		__cfq_slice_expired(cfqd, cfqq, preempted);
+}
+
 /*
  * 0
  * 0,1
@@ -801,16 +849,7 @@ static int cfq_get_next_prio_level(struct cfq_data *cfqd)
 
 static struct cfq_queue *cfq_set_active_queue(struct cfq_data *cfqd)
 {
-	struct cfq_queue *cfqq;
-
-	/*
-	 * if current queue is expired but not done with its requests yet,
-	 * wait for that to happen
-	 */
-	if ((cfqq = cfqd->active_queue) != NULL) {
-		if (cfq_cfqq_expired(cfqq) && cfq_cfqq_dispatched(cfqq))
-			return NULL;
-	}
+	struct cfq_queue *cfqq = NULL;
 
 	/*
 	 * if current list is non-empty, grab first entry. if it is empty,
@@ -837,66 +876,11 @@ static struct cfq_queue *cfq_set_active_queue(struct cfq_data *cfqd)
 	return cfqq;
 }
 
-/*
- * current cfqq expired its slice (or was too idle), select new one
- */
-static void
-__cfq_slice_expired(struct cfq_data *cfqd, struct cfq_queue *cfqq,
-		    int preempted)
-{
-	unsigned long now = jiffies;
-
-	if (cfq_cfqq_wait_request(cfqq))
-		del_timer(&cfqd->idle_slice_timer);
-
-	if (!preempted && !cfq_cfqq_dispatched(cfqq))
-		cfqq->service_last = now;
-
-	cfq_clear_cfqq_must_dispatch(cfqq);
-	cfq_clear_cfqq_wait_request(cfqq);
-
-	/*
-	 * store what was left of this slice, if the queue idled out
-	 * or was preempted
-	 */
-	if (time_after(cfqq->slice_end, now))
-		cfqq->slice_left = cfqq->slice_end - now;
-	else
-		cfqq->slice_left = 0;
-
-	if (cfq_cfqq_on_rr(cfqq))
-		cfq_resort_rr_list(cfqq, preempted);
-
-	if (cfqq == cfqd->active_queue)
-		cfqd->active_queue = NULL;
-
-	if (cfqd->active_cic) {
-		put_io_context(cfqd->active_cic->ioc);
-		cfqd->active_cic = NULL;
-	}
-
-	cfqd->dispatch_slice = 0;
-}
-
-static inline void cfq_slice_expired(struct cfq_data *cfqd, int preempted)
-{
-	struct cfq_queue *cfqq = cfqd->active_queue;
-
-	if (cfqq) {
-		/*
-		 * use deferred expiry, if there are requests in progress as
-		 * not to disturb the slice of the next queue
-		 */
-		if (cfq_cfqq_dispatched(cfqq))
-			cfq_mark_cfqq_expired(cfqq);
-		else
-			__cfq_slice_expired(cfqd, cfqq, preempted);
-	}
-}
-
 static int cfq_arm_slice_timer(struct cfq_data *cfqd, struct cfq_queue *cfqq)
 
 {
+	unsigned long sl;
+
 	WARN_ON(!RB_EMPTY(&cfqq->sort_list));
 	WARN_ON(cfqq != cfqd->active_queue);
 
@@ -916,13 +900,8 @@ static int cfq_arm_slice_timer(struct cfq_data *cfqd, struct cfq_queue *cfqq)
 	cfq_mark_cfqq_must_dispatch(cfqq);
 	cfq_mark_cfqq_wait_request(cfqq);
 
-	if (!timer_pending(&cfqd->idle_slice_timer)) {
-		unsigned long slice_left = min(cfqq->slice_end - 1, (unsigned long) cfqd->cfq_slice_idle);
-
-		cfqd->idle_slice_timer.expires = jiffies + slice_left;
-		add_timer(&cfqd->idle_slice_timer);
-	}
-
+	sl = min(cfqq->slice_end - 1, (unsigned long) cfqd->cfq_slice_idle);
+	mod_timer(&cfqd->idle_slice_timer, jiffies + sl);
 	return 1;
 }
 
@@ -1006,9 +985,6 @@ static struct cfq_queue *cfq_select_queue(struct cfq_data *cfqd)
 	if (!cfqq)
 		goto new_queue;
 
-	if (cfq_cfqq_expired(cfqq))
-		goto new_queue;
-
 	/*
 	 * slice has expired
 	 */
@@ -1181,10 +1157,8 @@ static void cfq_put_queue(struct cfq_queue *cfqq)
 	BUG_ON(cfqq->allocated[READ] + cfqq->allocated[WRITE]);
 	BUG_ON(cfq_cfqq_on_rr(cfqq));
 
-	if (unlikely(cfqd->active_queue == cfqq)) {
+	if (unlikely(cfqd->active_queue == cfqq))
 		__cfq_slice_expired(cfqd, cfqq, 0);
-		cfq_schedule_dispatch(cfqd);
-	}
 
 	cfq_put_cfqd(cfqq->cfqd);
 
@@ -1245,10 +1219,8 @@ static void cfq_exit_single_io_context(struct cfq_io_context *cic)
 
 	spin_lock(q->queue_lock);
 
-	if (unlikely(cic->cfqq == cfqd->active_queue)) {
+	if (unlikely(cic->cfqq == cfqd->active_queue))
 		__cfq_slice_expired(cfqd, cic->cfqq, 0);
-		cfq_schedule_dispatch(cfqd);
-	}
 
 	cfq_put_queue(cic->cfqq);
 	cic->cfqq = NULL;
@@ -1715,11 +1687,8 @@ static void cfq_completed_request(request_queue_t *q, struct request *rq)
 			cfqq->service_last = now;
 			cfq_resort_rr_list(cfqq, 0);
 		}
-		if (cfq_cfqq_expired(cfqq)) {
-			__cfq_slice_expired(cfqd, cfqq, 0);
 		cfq_schedule_dispatch(cfqd);
 	}
-	}
 
 	if (cfq_crq_is_sync(crq))
 		crq->io_context->last_end_request = now;