[PATCH v2] kyber: introduce kyber_depth_updated()

[Yang Yang <yang.yang@xxxxxxxx>]

Hang occurs when user changes the scheduler queue depth, by writing to
the 'nr_requests' sysfs file of that device.

The details of the environment that we found the problem are as follows:
  an eMMC block device
  total driver tags: 16
  default queue_depth: 32
  kqd->async_depth initialized in kyber_init_sched() with queue_depth=32

Then we change queue_depth to 256, by writing to the 'nr_requests' sysfs
file. But kqd->async_depth don't be updated after queue_depth changes.
Now the value of async depth is too small for queue_depth=256, this may
cause hang.

This patch introduces kyber_depth_updated(), so that kyber can update
async depth when queue depth changes.

Signed-off-by: Yang Yang <yang.yang@xxxxxxxx>
---
v2:
- Change the commit message
- Change from sbitmap::depth to 2^sbitmap::shift
---
 block/kyber-iosched.c | 29 +++++++++++++----------------
 1 file changed, 13 insertions(+), 16 deletions(-)

diff --git a/block/kyber-iosched.c b/block/kyber-iosched.c
index dc89199bc8c6..17215b6bf482 100644
--- a/block/kyber-iosched.c
+++ b/block/kyber-iosched.c
@@ -353,19 +353,9 @@ static void kyber_timer_fn(struct timer_list *t)
 	}
 }
 
-static unsigned int kyber_sched_tags_shift(struct request_queue *q)
-{
-	/*
-	 * All of the hardware queues have the same depth, so we can just grab
-	 * the shift of the first one.
-	 */
-	return q->queue_hw_ctx[0]->sched_tags->bitmap_tags->sb.shift;
-}
-
 static struct kyber_queue_data *kyber_queue_data_alloc(struct request_queue *q)
 {
 	struct kyber_queue_data *kqd;
-	unsigned int shift;
 	int ret = -ENOMEM;
 	int i;
 
@@ -400,9 +390,6 @@ static struct kyber_queue_data *kyber_queue_data_alloc(struct request_queue *q)
 		kqd->latency_targets[i] = kyber_latency_targets[i];
 	}
 
-	shift = kyber_sched_tags_shift(q);
-	kqd->async_depth = (1U << shift) * KYBER_ASYNC_PERCENT / 100U;
-
 	return kqd;
 
 err_buckets:
@@ -458,9 +445,19 @@ static void kyber_ctx_queue_init(struct kyber_ctx_queue *kcq)
 		INIT_LIST_HEAD(&kcq->rq_list[i]);
 }
 
-static int kyber_init_hctx(struct blk_mq_hw_ctx *hctx, unsigned int hctx_idx)
+static void kyber_depth_updated(struct blk_mq_hw_ctx *hctx)
 {
 	struct kyber_queue_data *kqd = hctx->queue->elevator->elevator_data;
+	struct blk_mq_tags *tags = hctx->sched_tags;
+	unsigned int shift = tags->bitmap_tags->sb.shift;
+
+	kqd->async_depth = (1U << shift) * KYBER_ASYNC_PERCENT / 100U;
+
+	sbitmap_queue_min_shallow_depth(tags->bitmap_tags, kqd->async_depth);
+}
+
+static int kyber_init_hctx(struct blk_mq_hw_ctx *hctx, unsigned int hctx_idx)
+{
 	struct kyber_hctx_data *khd;
 	int i;
 
@@ -502,8 +499,7 @@ static int kyber_init_hctx(struct blk_mq_hw_ctx *hctx, unsigned int hctx_idx)
 	khd->batching = 0;
 
 	hctx->sched_data = khd;
-	sbitmap_queue_min_shallow_depth(hctx->sched_tags->bitmap_tags,
-					kqd->async_depth);
+	kyber_depth_updated(hctx);
 
 	return 0;
 
@@ -1022,6 +1018,7 @@ static struct elevator_type kyber_sched = {
 		.completed_request = kyber_completed_request,
 		.dispatch_request = kyber_dispatch_request,
 		.has_work = kyber_has_work,
+		.depth_updated = kyber_depth_updated,
 	},
 #ifdef CONFIG_BLK_DEBUG_FS
 	.queue_debugfs_attrs = kyber_queue_debugfs_attrs,
-- 
2.17.1