1 files changed, 45 insertions, 14 deletions

diff --git a/block/blk-mq.c b/block/blk-mq.c
index 3a39184..a5dbd06 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -1789,7 +1789,8 @@ static void blk_mq_init_cpu_queues(struct request_queue *q,
 	}
 }
 
-static void blk_mq_map_swqueue(struct request_queue *q)
+static void blk_mq_map_swqueue(struct request_queue *q,
+			       const struct cpumask *online_mask)
 {
 	unsigned int i;
 	struct blk_mq_hw_ctx *hctx;
@@ -1806,7 +1807,7 @@ static void blk_mq_map_swqueue(struct request_queue *q)
 	 */
 	queue_for_each_ctx(q, ctx, i) {
 		/* If the cpu isn't online, the cpu is mapped to first hctx */
-		if (!cpu_online(i))
+		if (!cpumask_test_cpu(i, online_mask))
 			continue;
 
 		hctx = q->mq_ops->map_queue(q, i);
@@ -1852,7 +1853,7 @@ static void blk_mq_map_swqueue(struct request_queue *q)
 	}
 
 	queue_for_each_ctx(q, ctx, i) {
-		if (!cpu_online(i))
+		if (!cpumask_test_cpu(i, online_mask))
 			continue;
 
 		hctx = q->mq_ops->map_queue(q, i);
@@ -2037,13 +2038,15 @@ struct request_queue *blk_mq_init_allocated_queue(struct blk_mq_tag_set *set,
 	if (blk_mq_init_hw_queues(q, set))
 		goto err_hctxs;
 
+	get_online_cpus();
 	mutex_lock(&all_q_mutex);
 
 	list_add_tail(&q->all_q_node, &all_q_list);
 	blk_mq_add_queue_tag_set(set, q);
-	blk_mq_map_swqueue(q);
+	blk_mq_map_swqueue(q, cpu_online_mask);
 
 	mutex_unlock(&all_q_mutex);
+	put_online_cpus();
 
 	return q;
 
@@ -2080,13 +2083,14 @@ void blk_mq_free_queue(struct request_queue *q)
 }
 
 /* Basically redo blk_mq_init_queue with queue frozen */
-static void blk_mq_queue_reinit(struct request_queue *q)
+static void blk_mq_queue_reinit(struct request_queue *q,
+				const struct cpumask *online_mask)
 {
 	WARN_ON_ONCE(!atomic_read(&q->mq_freeze_depth));
 
 	blk_mq_sysfs_unregister(q);
 
-	blk_mq_update_queue_map(q->mq_map, q->nr_hw_queues);
+	blk_mq_update_queue_map(q->mq_map, q->nr_hw_queues, online_mask);
 
 	/*
 	 * redo blk_mq_init_cpu_queues and blk_mq_init_hw_queues. FIXME: maybe
@@ -2094,7 +2098,7 @@ static void blk_mq_queue_reinit(struct request_queue *q)
 	 * involves free and re-allocate memory, worthy doing?)
 	 */
 
-	blk_mq_map_swqueue(q);
+	blk_mq_map_swqueue(q, online_mask);
 
 	blk_mq_sysfs_register(q);
 }
@@ -2103,16 +2107,43 @@ static int blk_mq_queue_reinit_notify(struct notifier_block *nb,
 				      unsigned long action, void *hcpu)
 {
 	struct request_queue *q;
+	int cpu = (unsigned long)hcpu;
+	/*
+	 * New online cpumask which is going to be set in this hotplug event.
+	 * Declare this cpumasks as global as cpu-hotplug operation is invoked
+	 * one-by-one and dynamically allocating this could result in a failure.
+	 */
+	static struct cpumask online_new;
 
 	/*
-	 * Before new mappings are established, hotadded cpu might already
-	 * start handling requests. This doesn't break anything as we map
-	 * offline CPUs to first hardware queue. We will re-init the queue
-	 * below to get optimal settings.
+	 * Before hotadded cpu starts handling requests, new mappings must
+	 * be established.  Otherwise, these requests in hw queue might
+	 * never be dispatched.
+	 *
+	 * For example, there is a single hw queue (hctx) and two CPU queues
+	 * (ctx0 for CPU0, and ctx1 for CPU1).
+	 *
+	 * Now CPU1 is just onlined and a request is inserted into
+	 * ctx1->rq_list and set bit0 in pending bitmap as ctx1->index_hw is
+	 * still zero.
+	 *
+	 * And then while running hw queue, flush_busy_ctxs() finds bit0 is
+	 * set in pending bitmap and tries to retrieve requests in
+	 * hctx->ctxs[0]->rq_list.  But htx->ctxs[0] is a pointer to ctx0,
+	 * so the request in ctx1->rq_list is ignored.
 	 */
-	if (action != CPU_DEAD && action != CPU_DEAD_FROZEN &&
-	    action != CPU_ONLINE && action != CPU_ONLINE_FROZEN)
+	switch (action & ~CPU_TASKS_FROZEN) {
+	case CPU_DEAD:
+	case CPU_UP_CANCELED:
+		cpumask_copy(&online_new, cpu_online_mask);
+		break;
+	case CPU_UP_PREPARE:
+		cpumask_copy(&online_new, cpu_online_mask);
+		cpumask_set_cpu(cpu, &online_new);
+		break;
+	default:
 		return NOTIFY_OK;
+	}
 
 	mutex_lock(&all_q_mutex);
 
@@ -2136,7 +2167,7 @@ static int blk_mq_queue_reinit_notify(struct notifier_block *nb,
 	}
 
 	list_for_each_entry(q, &all_q_list, all_q_node)
-		blk_mq_queue_reinit(q);
+		blk_mq_queue_reinit(q, &online_new);
 
 	list_for_each_entry(q, &all_q_list, all_q_node)
 		blk_mq_unfreeze_queue(q);