On 8/21/19 2:15 AM, Ming Lei wrote:
diff --git a/block/blk-mq-sysfs.c b/block/blk-mq-sysfs.c
index 31bbf10d8149..a4cc40ddda86 100644
--- a/block/blk-mq-sysfs.c
+++ b/block/blk-mq-sysfs.c
@@ -247,7 +247,7 @@ void blk_mq_unregister_dev(struct device *dev, struct request_queue *q)
struct blk_mq_hw_ctx *hctx;
int i;
- lockdep_assert_held(&q->sysfs_lock);
+ lockdep_assert_held(&q->sysfs_dir_lock);
queue_for_each_hw_ctx(q, hctx, i)
blk_mq_unregister_hctx(hctx);
@@ -297,7 +297,7 @@ int __blk_mq_register_dev(struct device *dev, struct request_queue *q)
int ret, i;
WARN_ON_ONCE(!q->kobj.parent);
- lockdep_assert_held(&q->sysfs_lock);
+ lockdep_assert_held(&q->sysfs_dir_lock);
ret = kobject_add(q->mq_kobj, kobject_get(&dev->kobj), "%s", "mq");
if (ret < 0)
blk_mq_unregister_dev and __blk_mq_register_dev() are only used by
blk_register_queue() and blk_unregister_queue(). It is the
responsibility of the callers of these function to serialize request
queue registration and unregistration. Is it really necessary to hold a
mutex around the blk_mq_unregister_dev and __blk_mq_register_dev()
calls? Or in other words, can it ever happen that multiple threads
invoke one or both functions concurrently?
@@ -331,7 +331,7 @@ void blk_mq_sysfs_unregister(struct request_queue *q)
struct blk_mq_hw_ctx *hctx;
int i;
- mutex_lock(&q->sysfs_lock);
+ mutex_lock(&q->sysfs_dir_lock);
if (!q->mq_sysfs_init_done)
goto unlock;
@@ -339,7 +339,7 @@ void blk_mq_sysfs_unregister(struct request_queue *q)
blk_mq_unregister_hctx(hctx);
unlock:
- mutex_unlock(&q->sysfs_lock);
+ mutex_unlock(&q->sysfs_dir_lock);
}
int blk_mq_sysfs_register(struct request_queue *q)
@@ -347,7 +347,7 @@ int blk_mq_sysfs_register(struct request_queue *q)
struct blk_mq_hw_ctx *hctx;
int i, ret = 0;
- mutex_lock(&q->sysfs_lock);
+ mutex_lock(&q->sysfs_dir_lock);
if (!q->mq_sysfs_init_done)
goto unlock;
@@ -358,7 +358,7 @@ int blk_mq_sysfs_register(struct request_queue *q)
}
unlock:
- mutex_unlock(&q->sysfs_lock);
+ mutex_unlock(&q->sysfs_dir_lock);
return ret;
}
blk_mq_sysfs_unregister() and blk_mq_sysfs_register() are only used by
__blk_mq_update_nr_hw_queues(). Calls to that function are serialized by
the tag_list_lock mutex. Is it really necessary to use any locking
inside these functions?
diff --git a/block/blk-sysfs.c b/block/blk-sysfs.c
index 5b0b5224cfd4..5941a0176f87 100644
--- a/block/blk-sysfs.c
+++ b/block/blk-sysfs.c
@@ -938,6 +938,7 @@ int blk_register_queue(struct gendisk *disk)
int ret;
struct device *dev = disk_to_dev(disk);
struct request_queue *q = disk->queue;
+ bool has_elevator = false;
if (WARN_ON(!q))
return -ENXIO;
@@ -945,7 +946,6 @@ int blk_register_queue(struct gendisk *disk)
WARN_ONCE(blk_queue_registered(q),
"%s is registering an already registered queue\n",
kobject_name(&dev->kobj));
- blk_queue_flag_set(QUEUE_FLAG_REGISTERED, q);
/*
* SCSI probing may synchronously create and destroy a lot of
@@ -966,7 +966,7 @@ int blk_register_queue(struct gendisk *disk)
return ret;
/* Prevent changes through sysfs until registration is completed. */
- mutex_lock(&q->sysfs_lock);
+ mutex_lock(&q->sysfs_dir_lock);
ret = kobject_add(&q->kobj, kobject_get(&dev->kobj), "%s", "queue");
if (ret < 0) {
@@ -987,26 +987,37 @@ int blk_register_queue(struct gendisk *disk)
blk_mq_debugfs_register(q);
}
- kobject_uevent(&q->kobj, KOBJ_ADD);
-
- wbt_enable_default(q);
-
- blk_throtl_register_queue(q);
-
+ /*
+ * The queue's kobject ADD uevent isn't sent out, also the
+ * flag of QUEUE_FLAG_REGISTERED isn't set yet, so elevator
+ * switch won't happen at all.
+ */
if (q->elevator) {
- ret = elv_register_queue(q);
+ ret = elv_register_queue(q, false);
if (ret) {
- mutex_unlock(&q->sysfs_lock);
- kobject_uevent(&q->kobj, KOBJ_REMOVE);
+ mutex_unlock(&q->sysfs_dir_lock);
kobject_del(&q->kobj);
blk_trace_remove_sysfs(dev);
kobject_put(&dev->kobj);
return ret;
}
+ has_elevator = true;
}
+
+ mutex_lock(&q->sysfs_lock);
+ blk_queue_flag_set(QUEUE_FLAG_REGISTERED, q);
+ wbt_enable_default(q);
+ blk_throtl_register_queue(q);
+ mutex_unlock(&q->sysfs_lock);
+
+ /* Now everything is ready and send out KOBJ_ADD uevent */
+ kobject_uevent(&q->kobj, KOBJ_ADD);
+ if (has_elevator)
+ kobject_uevent(&q->elevator->kobj, KOBJ_ADD);
+
ret = 0;
unlock:
- mutex_unlock(&q->sysfs_lock);
+ mutex_unlock(&q->sysfs_dir_lock);
return ret;
}
My understanding is that the mutex_lock() / mutex_unlock() calls in this
function are necessary today to prevent concurrent changes of the
scheduler from this function and from sysfs. If the
kobject_uevent(KOBJ_ADD) call is moved, does that mean that all
mutex_lock() / mutex_unlock() calls can be left out from this function?
EXPORT_SYMBOL_GPL(blk_register_queue);
@@ -1021,6 +1032,7 @@ EXPORT_SYMBOL_GPL(blk_register_queue);
void blk_unregister_queue(struct gendisk *disk)
{
struct request_queue *q = disk->queue;
+ bool has_elevator;
if (WARN_ON(!q))
return;
@@ -1035,25 +1047,25 @@ void blk_unregister_queue(struct gendisk *disk)
* concurrent elv_iosched_store() calls.
*/
mutex_lock(&q->sysfs_lock);
-
blk_queue_flag_clear(QUEUE_FLAG_REGISTERED, q);
+ has_elevator = !!q->elevator;
+ 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.
*/
if (queue_is_mq(q))
blk_mq_unregister_dev(disk_to_dev(disk), q);
- mutex_unlock(&q->sysfs_lock);
kobject_uevent(&q->kobj, KOBJ_REMOVE);
kobject_del(&q->kobj);
blk_trace_remove_sysfs(disk_to_dev(disk));
- mutex_lock(&q->sysfs_lock);
- if (q->elevator)
+ if (has_elevator)
elv_unregister_queue(q);
- mutex_unlock(&q->sysfs_lock);
+ mutex_unlock(&q->sysfs_dir_lock);
kobject_put(&disk_to_dev(disk)->kobj);
}
If this function would call kobject_del(&q->kobj) before doing anything
else, does that mean that all mutex_lock() / mutex_unlock() calls can be
left out from this function?
Thanks,
Bart.
