block: use same block debugfs directory for blk-mq and blktrace

When I added the blk-mq debugging information to debugfs, I didn't
notice that blktrace also creates a "block" directory in debugfs. Make
them use the same dentry, now created in the core block code. Based on a
patch from Jens.
Signed-off-by: Omar Sandoval <osandov@fb.com>
Signed-off-by: Jens Axboe <axboe@fb.com>

block/blk-core.c

@@ -33,6 +33,7 @@
 #include <linux/ratelimit.h>
 #include <linux/pm_runtime.h>
 #include <linux/blk-cgroup.h>
+#include <linux/debugfs.h>
 
 #define CREATE_TRACE_POINTS
 #include <trace/events/block.h>
@@ -42,6 +43,10 @@
 #include "blk-mq-sched.h"
 #include "blk-wbt.h"
 
+#ifdef CONFIG_DEBUG_FS
+struct dentry *blk_debugfs_root;
+#endif
+
 EXPORT_TRACEPOINT_SYMBOL_GPL(block_bio_remap);
 EXPORT_TRACEPOINT_SYMBOL_GPL(block_rq_remap);
 EXPORT_TRACEPOINT_SYMBOL_GPL(block_bio_complete);
@@ -3441,5 +3446,9 @@ int __init blk_dev_init(void)
 	blk_requestq_cachep = kmem_cache_create("request_queue",
 			sizeof(struct request_queue), 0, SLAB_PANIC, NULL);
 
+#ifdef CONFIG_DEBUG_FS
+	blk_debugfs_root = debugfs_create_dir("block", NULL);
+#endif
+
 	return 0;
 }

block/blk-mq-debugfs.c

@@ -19,6 +19,7 @@
 #include <linux/debugfs.h>
 
 #include <linux/blk-mq.h>
+#include "blk.h"
 #include "blk-mq.h"
 #include "blk-mq-tag.h"
 
@@ -28,8 +29,6 @@ struct blk_mq_debugfs_attr {
 	const struct file_operations *fops;
 };
 
-static struct dentry *block_debugfs_root;
-
 static int blk_mq_debugfs_seq_open(struct inode *inode, struct file *file,
 				   const struct seq_operations *ops)
 {
@@ -665,10 +664,10 @@ static const struct blk_mq_debugfs_attr blk_mq_debugfs_ctx_attrs[] = {
 
 int blk_mq_debugfs_register(struct request_queue *q, const char *name)
 {
-	if (!block_debugfs_root)
+	if (!blk_debugfs_root)
 		return -ENOENT;
 
-	q->debugfs_dir = debugfs_create_dir(name, block_debugfs_root);
+	q->debugfs_dir = debugfs_create_dir(name, blk_debugfs_root);
 	if (!q->debugfs_dir)
 		goto err;
 
@@ -771,8 +770,3 @@ void blk_mq_debugfs_unregister_hctxs(struct request_queue *q)
 	debugfs_remove_recursive(q->mq_debugfs_dir);
 	q->mq_debugfs_dir = NULL;
 }
-
-void blk_mq_debugfs_init(void)
-{
-	block_debugfs_root = debugfs_create_dir("block", NULL);
-}

block/blk-mq.c

@@ -2817,8 +2817,6 @@ void blk_mq_enable_hotplug(void)
 
 static int __init blk_mq_init(void)
 {
-	blk_mq_debugfs_init();
-
 	cpuhp_setup_state_multi(CPUHP_BLK_MQ_DEAD, "block/mq:dead", NULL,
 				blk_mq_hctx_notify_dead);
 

block/blk-mq.h

@@ -85,16 +85,11 @@ extern void blk_mq_hctx_kobj_init(struct blk_mq_hw_ctx *hctx);
  * debugfs helpers
  */
 #ifdef CONFIG_BLK_DEBUG_FS
-void blk_mq_debugfs_init(void);
 int blk_mq_debugfs_register(struct request_queue *q, const char *name);
 void blk_mq_debugfs_unregister(struct request_queue *q);
 int blk_mq_debugfs_register_hctxs(struct request_queue *q);
 void blk_mq_debugfs_unregister_hctxs(struct request_queue *q);
 #else
-static inline void blk_mq_debugfs_init(void)
-{
-}
-
 static inline int blk_mq_debugfs_register(struct request_queue *q,
 					  const char *name)
 {

block/blk.h

@@ -14,6 +14,10 @@
 /* Max future timer expiry for timeouts */
 #define BLK_MAX_TIMEOUT		(5 * HZ)
 
+#ifdef CONFIG_DEBUG_FS
+extern struct dentry *blk_debugfs_root;
+#endif
+
 struct blk_flush_queue {
 	unsigned int		flush_queue_delayed:1;
 	unsigned int		flush_pending_idx:1;

kernel/trace/blktrace.c

@@ -28,6 +28,8 @@
 #include <linux/uaccess.h>
 #include <linux/list.h>
 
+#include "../../block/blk.h"
+
 #include <trace/events/block.h>
 
 #include "trace_output.h"
@@ -292,9 +294,6 @@ static void __blk_add_trace(struct blk_trace *bt, sector_t sector, int bytes,
 	local_irq_restore(flags);
 }
 
-static struct dentry *blk_tree_root;
-static DEFINE_MUTEX(blk_tree_mutex);
-
 static void blk_trace_free(struct blk_trace *bt)
 {
 	debugfs_remove(bt->msg_file);
@@ -468,17 +467,10 @@ static int do_blk_trace_setup(struct request_queue *q, char *name, dev_t dev,
 
 	ret = -ENOENT;
 
-	mutex_lock(&blk_tree_mutex);
-	if (!blk_tree_root) {
-		blk_tree_root = debugfs_create_dir("block", NULL);
-		if (!blk_tree_root) {
-			mutex_unlock(&blk_tree_mutex);
-			goto err;
-		}
-	}
-	mutex_unlock(&blk_tree_mutex);
+	if (!blk_debugfs_root)
+		goto err;
 
-	dir = debugfs_create_dir(buts->name, blk_tree_root);
+	dir = debugfs_create_dir(buts->name, blk_debugfs_root);
 
 	if (!dir)
 		goto err;