[RFC PATCHv2 1/2] block: get rid of request queue ->sysfs_dir_lock

[Nilay Shroff <nilay@linux.ibm.com>]

The request queue uses ->sysfs_dir_lock for protecting the addition/
deletion of kobject entries under sysfs while we register/unregister
blk-mq. However kobject addition/deletion is already protected with
kernfs/sysfs internal synchronization primitives. So use of q->sysfs_
dir_lock seems redundant.

Moreover, q->sysfs_dir_lock is also used at few other callsites along
with q->sysfs_lock for protecting the addition/deletion of kojects.
One such example is when we register with sysfs a set of independent
access ranges for a disk. Here as well we could get rid off q->sysfs_
dir_lock and only use q->sysfs_lock.

The only variable which q->sysfs_dir_lock appears to protect is q->
mq_sysfs_init_done which is set/unset while registering/unregistering
blk-mq with sysfs. But use of q->mq_sysfs_init_done could be easily
replaced using queue registered bit QUEUE_FLAG_REGISTERED.

So with this patch we remove q->sysfs_dir_lock from each callsite
and replace q->mq_sysfs_init_done using QUEUE_FLAG_REGISTERED.

Signed-off-by: Nilay Shroff <nilay@linux.ibm.com>
---
 block/blk-core.c       |  1 -
 block/blk-ia-ranges.c  |  4 ----
 block/blk-mq-sysfs.c   | 23 +++++------------------
 block/blk-sysfs.c      |  5 -----
 include/linux/blkdev.h |  3 ---
 5 files changed, 5 insertions(+), 31 deletions(-)

diff --git a/block/blk-core.c b/block/blk-core.c
index 32fb28a6372c..d6c4fa3943b5 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -430,7 +430,6 @@ struct request_queue *blk_alloc_queue(struct queue_limits *lim, int node_id)
 	refcount_set(&q->refs, 1);
 	mutex_init(&q->debugfs_mutex);
 	mutex_init(&q->sysfs_lock);
-	mutex_init(&q->sysfs_dir_lock);
 	mutex_init(&q->limits_lock);
 	mutex_init(&q->rq_qos_mutex);
 	spin_lock_init(&q->queue_lock);
diff --git a/block/blk-ia-ranges.c b/block/blk-ia-ranges.c
index c9eb4241e048..d479f5481b66 100644
--- a/block/blk-ia-ranges.c
+++ b/block/blk-ia-ranges.c
@@ -111,7 +111,6 @@ int disk_register_independent_access_ranges(struct gendisk *disk)
 	struct request_queue *q = disk->queue;
 	int i, ret;
 
-	lockdep_assert_held(&q->sysfs_dir_lock);
 	lockdep_assert_held(&q->sysfs_lock);
 
 	if (!iars)
@@ -155,7 +154,6 @@ void disk_unregister_independent_access_ranges(struct gendisk *disk)
 	struct blk_independent_access_ranges *iars = disk->ia_ranges;
 	int i;
 
-	lockdep_assert_held(&q->sysfs_dir_lock);
 	lockdep_assert_held(&q->sysfs_lock);
 
 	if (!iars)
@@ -289,7 +287,6 @@ void disk_set_independent_access_ranges(struct gendisk *disk,
 {
 	struct request_queue *q = disk->queue;
 
-	mutex_lock(&q->sysfs_dir_lock);
 	mutex_lock(&q->sysfs_lock);
 	if (iars && !disk_check_ia_ranges(disk, iars)) {
 		kfree(iars);
@@ -313,6 +310,5 @@ void disk_set_independent_access_ranges(struct gendisk *disk,
 		disk_register_independent_access_ranges(disk);
 unlock:
 	mutex_unlock(&q->sysfs_lock);
-	mutex_unlock(&q->sysfs_dir_lock);
 }
 EXPORT_SYMBOL_GPL(disk_set_independent_access_ranges);
diff --git a/block/blk-mq-sysfs.c b/block/blk-mq-sysfs.c
index 156e9bb07abf..6113328abd70 100644
--- a/block/blk-mq-sysfs.c
+++ b/block/blk-mq-sysfs.c
@@ -223,8 +223,6 @@ int blk_mq_sysfs_register(struct gendisk *disk)
 	unsigned long i, j;
 	int ret;
 
-	lockdep_assert_held(&q->sysfs_dir_lock);
-
 	ret = kobject_add(q->mq_kobj, &disk_to_dev(disk)->kobj, "mq");
 	if (ret < 0)
 		goto out;
@@ -237,7 +235,6 @@ int blk_mq_sysfs_register(struct gendisk *disk)
 			goto unreg;
 	}
 
-	q->mq_sysfs_init_done = true;
 
 out:
 	return ret;
@@ -259,15 +256,12 @@ void blk_mq_sysfs_unregister(struct gendisk *disk)
 	struct blk_mq_hw_ctx *hctx;
 	unsigned long i;
 
-	lockdep_assert_held(&q->sysfs_dir_lock);
 
 	queue_for_each_hw_ctx(q, hctx, i)
 		blk_mq_unregister_hctx(hctx);
 
 	kobject_uevent(q->mq_kobj, KOBJ_REMOVE);
 	kobject_del(q->mq_kobj);
-
-	q->mq_sysfs_init_done = false;
 }
 
 void blk_mq_sysfs_unregister_hctxs(struct request_queue *q)
@@ -275,15 +269,11 @@ void blk_mq_sysfs_unregister_hctxs(struct request_queue *q)
 	struct blk_mq_hw_ctx *hctx;
 	unsigned long i;
 
-	mutex_lock(&q->sysfs_dir_lock);
-	if (!q->mq_sysfs_init_done)
-		goto unlock;
+	if (!blk_queue_registered(q))
+		return;
 
 	queue_for_each_hw_ctx(q, hctx, i)
 		blk_mq_unregister_hctx(hctx);
-
-unlock:
-	mutex_unlock(&q->sysfs_dir_lock);
 }
 
 int blk_mq_sysfs_register_hctxs(struct request_queue *q)
@@ -292,9 +282,8 @@ int blk_mq_sysfs_register_hctxs(struct request_queue *q)
 	unsigned long i;
 	int ret = 0;
 
-	mutex_lock(&q->sysfs_dir_lock);
-	if (!q->mq_sysfs_init_done)
-		goto unlock;
+	if (!blk_queue_registered(q))
+		goto out;
 
 	queue_for_each_hw_ctx(q, hctx, i) {
 		ret = blk_mq_register_hctx(hctx);
@@ -302,8 +291,6 @@ int blk_mq_sysfs_register_hctxs(struct request_queue *q)
 			break;
 	}
 
-unlock:
-	mutex_unlock(&q->sysfs_dir_lock);
-
+out:
 	return ret;
 }
diff --git a/block/blk-sysfs.c b/block/blk-sysfs.c
index e09b455874bf..7b970e6765e7 100644
--- a/block/blk-sysfs.c
+++ b/block/blk-sysfs.c
@@ -764,7 +764,6 @@ int blk_register_queue(struct gendisk *disk)
 	struct request_queue *q = disk->queue;
 	int ret;
 
-	mutex_lock(&q->sysfs_dir_lock);
 	kobject_init(&disk->queue_kobj, &blk_queue_ktype);
 	ret = kobject_add(&disk->queue_kobj, &disk_to_dev(disk)->kobj, "queue");
 	if (ret < 0)
@@ -805,7 +804,6 @@ int blk_register_queue(struct gendisk *disk)
 	if (q->elevator)
 		kobject_uevent(&q->elevator->kobj, KOBJ_ADD);
 	mutex_unlock(&q->sysfs_lock);
-	mutex_unlock(&q->sysfs_dir_lock);
 
 	/*
 	 * SCSI probing may synchronously create and destroy a lot of
@@ -830,7 +828,6 @@ int blk_register_queue(struct gendisk *disk)
 	mutex_unlock(&q->sysfs_lock);
 out_put_queue_kobj:
 	kobject_put(&disk->queue_kobj);
-	mutex_unlock(&q->sysfs_dir_lock);
 	return ret;
 }
 
@@ -861,7 +858,6 @@ void blk_unregister_queue(struct gendisk *disk)
 	blk_queue_flag_clear(QUEUE_FLAG_REGISTERED, q);
 	mutex_unlock(&q->sysfs_lock);
 
-	mutex_lock(&q->sysfs_dir_lock);
 	/*
 	 * Remove the sysfs attributes before unregistering the queue data
 	 * structures that can be modified through sysfs.
@@ -878,7 +874,6 @@ void blk_unregister_queue(struct gendisk *disk)
 	/* Now that we've deleted all child objects, we can delete the queue. */
 	kobject_uevent(&disk->queue_kobj, KOBJ_REMOVE);
 	kobject_del(&disk->queue_kobj);
-	mutex_unlock(&q->sysfs_dir_lock);
 
 	blk_debugfs_remove(disk);
 }
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index 76f0a4e7c2e5..248416ecd01c 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -561,7 +561,6 @@ struct request_queue {
 	struct list_head	flush_list;
 
 	struct mutex		sysfs_lock;
-	struct mutex		sysfs_dir_lock;
 	struct mutex		limits_lock;
 
 	/*
@@ -605,8 +604,6 @@ struct request_queue {
 	 * Serializes all debugfs metadata operations using the above dentries.
 	 */
 	struct mutex		debugfs_mutex;
-
-	bool			mq_sysfs_init_done;
 };
 
 /* Keep blk_queue_flag_name[] in sync with the definitions below */
-- 
2.47.1