[PATCH v5 01/10] blk-mq: Register /queue/mq after having registered /queue

Bart Van Assche
2017-04-25T20:37:36Z

A later patch in this series will modify blk_mq_debugfs_register()
such that it uses q->kobj.parent to determine the name of a
request queue. Hence make sure that that pointer is initialized
before blk_mq_debugfs_register() is called. To avoid lock inversion,
protect sysfs / debugfs registration with the queue sysfs_lock
instead of the global mutex all_q_mutex.

Signed-off-by: Bart Van Assche <bart.vanassche@sandisk.com>
Reviewed-by: Hannes Reinecke <hare@suse.com>
Reviewed-by: Omar Sandoval <osandov@fb.com>
---
block/blk-mq-sysfs.c | 35 ++++++++++++++++++++++++++++-------
block/blk-mq.h | 1 +
block/blk-sysfs.c | 6 +++---
3 files changed, 32 insertions(+), 10 deletions(-)

diff --git a/block/blk-mq-sysfs.c b/block/blk-mq-sysfs.c
index d745ab81033a..a2dbb1a48e72 100644
--- a/block/blk-mq-sysfs.c
+++ b/block/blk-mq-sysfs.c
@@ -253,6 +253,8 @@ static 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);
+
queue_for_each_hw_ctx(q, hctx, i)
blk_mq_unregister_hctx(hctx);

@@ -267,9 +269,9 @@ static void __blk_mq_unregister_dev(struct device *dev, struct request_queue *q)

void blk_mq_unregister_dev(struct device *dev, struct request_queue *q)
{
- blk_mq_disable_hotplug();
+ mutex_lock(&q->sysfs_lock);
__blk_mq_unregister_dev(dev, q);
- blk_mq_enable_hotplug();
+ mutex_unlock(&q->sysfs_lock);
}

void blk_mq_hctx_kobj_init(struct blk_mq_hw_ctx *hctx)
@@ -302,12 +304,13 @@ void blk_mq_sysfs_init(struct request_queue *q)
}
}

-int blk_mq_register_dev(struct device *dev, struct request_queue *q)
+int __blk_mq_register_dev(struct device *dev, struct request_queue *q)
{
struct blk_mq_hw_ctx *hctx;
int ret, i;

- blk_mq_disable_hotplug();
+ WARN_ON_ONCE(!q->kobj.parent);
+ lockdep_assert_held(&q->sysfs_lock);

ret = kobject_add(&q->mq_kobj, kobject_get(&dev->kobj), "%s", "mq");
if (ret < 0)
@@ -327,8 +330,18 @@ int blk_mq_register_dev(struct device *dev, struct request_queue *q)
__blk_mq_unregister_dev(dev, q);
else
q->mq_sysfs_init_done = true;
+
out:
- blk_mq_enable_hotplug();
+ return ret;
+}
+
+int blk_mq_register_dev(struct device *dev, struct request_queue *q)
+{
+ int ret;
+
+ mutex_lock(&q->sysfs_lock);
+ ret = __blk_mq_register_dev(dev, q);
+ mutex_unlock(&q->sysfs_lock);

return ret;
}
@@ -339,13 +352,17 @@ void blk_mq_sysfs_unregister(struct request_queue *q)
struct blk_mq_hw_ctx *hctx;
int i;

+ mutex_lock(&q->sysfs_lock);
if (!q->mq_sysfs_init_done)
- return;
+ goto unlock;

blk_mq_debugfs_unregister_hctxs(q);

queue_for_each_hw_ctx(q, hctx, i)
blk_mq_unregister_hctx(hctx);
+
+unlock:
+ mutex_unlock(&q->sysfs_lock);
}

int blk_mq_sysfs_register(struct request_queue *q)
@@ -353,8 +370,9 @@ int blk_mq_sysfs_register(struct request_queue *q)
struct blk_mq_hw_ctx *hctx;
int i, ret = 0;

+ mutex_lock(&q->sysfs_lock);
if (!q->mq_sysfs_init_done)
- return ret;
+ goto unlock;

blk_mq_debugfs_register_hctxs(q);

@@ -364,5 +382,8 @@ int blk_mq_sysfs_register(struct request_queue *q)
break;
}

+unlock:
+ mutex_unlock(&q->sysfs_lock);
+
return ret;
}
diff --git a/block/blk-mq.h b/block/blk-mq.h
index 524f44742816..7d955c756810 100644
--- a/block/blk-mq.h
+++ b/block/blk-mq.h
@@ -78,6 +78,7 @@ static inline struct blk_mq_hw_ctx *blk_mq_map_queue(struct request_queue *q,
*/
extern void blk_mq_sysfs_init(struct request_queue *q);
extern void blk_mq_sysfs_deinit(struct request_queue *q);
+extern int __blk_mq_register_dev(struct device *dev, struct request_queue *q);
extern int blk_mq_sysfs_register(struct request_queue *q);
extern void blk_mq_sysfs_unregister(struct request_queue *q);
extern void blk_mq_hctx_kobj_init(struct blk_mq_hw_ctx *hctx);
diff --git a/block/blk-sysfs.c b/block/blk-sysfs.c
index f85723332288..3f37813ccbaf 100644
--- a/block/blk-sysfs.c
+++ b/block/blk-sysfs.c
@@ -877,9 +877,6 @@ int blk_register_queue(struct gendisk *disk)
if (ret)
return ret;

- if (q->mq_ops)
- blk_mq_register_dev(dev, q);
-
/* Prevent changes through sysfs until registration is completed. */
mutex_lock(&q->sysfs_lock);

@@ -889,6 +886,9 @@ int blk_register_queue(struct gendisk *disk)
goto unlock;
}

+ if (q->mq_ops)
+ __blk_mq_register_dev(dev, q);
+
kobject_uevent(&q->kobj, KOBJ_ADD);

wbt_enable_default(q);
--
2.12.2