[PATCH 1/7] block: remove hctx->debugfs_dir

[Ming Lei <ming.lei@xxxxxxxxxx>]

For each hctx, its debugfs path is fixed, which can be queried from
its parent dentry and hctx queue num, so it isn't necessary to cache
it in hctx structure because it isn't used in fast path.

Signed-off-by: Ming Lei <ming.lei@xxxxxxxxxx>
---
 block/blk-mq-debugfs.c | 47 ++++++++++++++++++++++++++++++++----------
 include/linux/blk-mq.h |  5 -----
 2 files changed, 36 insertions(+), 16 deletions(-)

diff --git a/block/blk-mq-debugfs.c b/block/blk-mq-debugfs.c
index adf5f0697b6b..16260bba4d11 100644
--- a/block/blk-mq-debugfs.c
+++ b/block/blk-mq-debugfs.c
@@ -633,8 +633,7 @@ void blk_mq_debugfs_register(struct request_queue *q)
 
 	/* Similarly, blk_mq_init_hctx() couldn't do this previously. */
 	queue_for_each_hw_ctx(q, hctx, i) {
-		if (!hctx->debugfs_dir)
-			blk_mq_debugfs_register_hctx(q, hctx);
+		blk_mq_debugfs_register_hctx(q, hctx);
 		if (q->elevator && !hctx->sched_debugfs_dir)
 			blk_mq_debugfs_register_sched_hctx(q, hctx);
 	}
@@ -649,14 +648,28 @@ void blk_mq_debugfs_register(struct request_queue *q)
 	}
 }
 
+static __must_check struct dentry *blk_mq_get_hctx_entry(
+		struct blk_mq_hw_ctx *hctx)
+{
+	char name[20];
+
+	snprintf(name, sizeof(name), "hctx%u", hctx->queue_num);
+	return debugfs_lookup(name, hctx->queue->debugfs_dir);
+}
+
 static void blk_mq_debugfs_register_ctx(struct blk_mq_hw_ctx *hctx,
 					struct blk_mq_ctx *ctx)
 {
+	struct dentry *hctx_dir = blk_mq_get_hctx_entry(hctx);
 	struct dentry *ctx_dir;
 	char name[20];
 
+	if (IS_ERR_OR_NULL(hctx_dir))
+		return;
+
 	snprintf(name, sizeof(name), "cpu%u", ctx->cpu);
-	ctx_dir = debugfs_create_dir(name, hctx->debugfs_dir);
+	ctx_dir = debugfs_create_dir(name, hctx_dir);
+	dput(hctx_dir);
 
 	debugfs_create_files(ctx_dir, ctx, blk_mq_debugfs_ctx_attrs);
 }
@@ -664,6 +677,7 @@ static void blk_mq_debugfs_register_ctx(struct blk_mq_hw_ctx *hctx,
 void blk_mq_debugfs_register_hctx(struct request_queue *q,
 				  struct blk_mq_hw_ctx *hctx)
 {
+	struct dentry *hctx_dir;
 	struct blk_mq_ctx *ctx;
 	char name[20];
 	int i;
@@ -672,9 +686,11 @@ void blk_mq_debugfs_register_hctx(struct request_queue *q,
 		return;
 
 	snprintf(name, sizeof(name), "hctx%u", hctx->queue_num);
-	hctx->debugfs_dir = debugfs_create_dir(name, q->debugfs_dir);
+	hctx_dir = debugfs_create_dir(name, q->debugfs_dir);
+	if (IS_ERR_OR_NULL(hctx_dir))
+		return;
 
-	debugfs_create_files(hctx->debugfs_dir, hctx, blk_mq_debugfs_hctx_attrs);
+	debugfs_create_files(hctx_dir, hctx, blk_mq_debugfs_hctx_attrs);
 
 	hctx_for_each_ctx(hctx, ctx, i)
 		blk_mq_debugfs_register_ctx(hctx, ctx);
@@ -682,11 +698,18 @@ void blk_mq_debugfs_register_hctx(struct request_queue *q,
 
 void blk_mq_debugfs_unregister_hctx(struct blk_mq_hw_ctx *hctx)
 {
+	struct dentry *hctx_dir;
+
 	if (!hctx->queue->debugfs_dir)
 		return;
-	debugfs_remove_recursive(hctx->debugfs_dir);
+
+	hctx_dir = blk_mq_get_hctx_entry(hctx);
+	if (IS_ERR_OR_NULL(hctx_dir))
+		return;
+
+	debugfs_remove_recursive(hctx_dir);
 	hctx->sched_debugfs_dir = NULL;
-	hctx->debugfs_dir = NULL;
+	dput(hctx_dir);
 }
 
 void blk_mq_debugfs_register_hctxs(struct request_queue *q)
@@ -780,6 +803,7 @@ void blk_mq_debugfs_register_rqos(struct rq_qos *rqos)
 void blk_mq_debugfs_register_sched_hctx(struct request_queue *q,
 					struct blk_mq_hw_ctx *hctx)
 {
+	struct dentry *hctx_dir = blk_mq_get_hctx_entry(hctx);
 	struct elevator_type *e = q->elevator->type;
 
 	lockdep_assert_held(&q->debugfs_mutex);
@@ -789,16 +813,17 @@ void blk_mq_debugfs_register_sched_hctx(struct request_queue *q,
 	 * We will be called again later on with appropriate parent debugfs
 	 * directory from blk_register_queue()
 	 */
-	if (!hctx->debugfs_dir)
+	if (IS_ERR_OR_NULL(hctx_dir))
 		return;
 
 	if (!e->hctx_debugfs_attrs)
-		return;
+		goto exit;
 
-	hctx->sched_debugfs_dir = debugfs_create_dir("sched",
-						     hctx->debugfs_dir);
+	hctx->sched_debugfs_dir = debugfs_create_dir("sched", hctx_dir);
 	debugfs_create_files(hctx->sched_debugfs_dir, hctx,
 			     e->hctx_debugfs_attrs);
+exit:
+	dput(hctx_dir);
 }
 
 void blk_mq_debugfs_unregister_sched_hctx(struct blk_mq_hw_ctx *hctx)
diff --git a/include/linux/blk-mq.h b/include/linux/blk-mq.h
index 9ebb53f031cd..8c8682491403 100644
--- a/include/linux/blk-mq.h
+++ b/include/linux/blk-mq.h
@@ -427,11 +427,6 @@ struct blk_mq_hw_ctx {
 	struct kobject		kobj;
 
 #ifdef CONFIG_BLK_DEBUG_FS
-	/**
-	 * @debugfs_dir: debugfs directory for this hardware queue. Named
-	 * as cpu<cpu_number>.
-	 */
-	struct dentry		*debugfs_dir;
 	/** @sched_debugfs_dir:	debugfs directory for the scheduler. */
 	struct dentry		*sched_debugfs_dir;
 #endif
-- 
2.47.0