Currently rq-qos debugfs entries are created from rq_qos_add(), while
rq_qos_add() can be called while queue is still frozen. This can
deadlock because creating new entries can trigger fs reclaim.

Fix this problem by delaying creating rq-qos debugfs entries after queue
is unfrozen.

- For wbt, 1) it can be initialized by default, fix it by calling new
  helper after wbt_init() from wbt_enable_default; 2) it can be
  initialized by sysfs, fix it by calling new helper after queue is
  unfrozen from queue_wb_lat_store().
- For iocost and iolatency, they can only be initialized by blkcg
  configuration, fix by calling the new helper from blkg_conf_end().

Signed-off-by: Yu Kuai <yukuai@fnnas.com>
---
 block/blk-cgroup.c | 38 +++++++++++++++++++++++++++++---------
 block/blk-rq-qos.c |  7 -------
 block/blk-sysfs.c  |  4 ++++
 block/blk-wbt.c    |  6 +++++-
 4 files changed, 38 insertions(+), 17 deletions(-)

diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c
index 3cffb68ba5d8..ad3bd43b2859 100644
--- a/block/blk-cgroup.c
+++ b/block/blk-cgroup.c
@@ -33,6 +33,7 @@
 #include "blk-cgroup.h"
 #include "blk-ioprio.h"
 #include "blk-throttle.h"
+#include "blk-mq-debugfs.h"
 
 static void __blkcg_rstat_flush(struct blkcg *blkcg, int cpu);
 
@@ -966,14 +967,7 @@ int blkg_conf_prep(struct blkcg *blkcg, const struct blkcg_policy *pol,
 }
 EXPORT_SYMBOL_GPL(blkg_conf_prep);
 
-/**
- * blkg_conf_exit - clean up per-blkg config update
- * @ctx: blkg_conf_ctx initialized with blkg_conf_init()
- *
- * Clean up after per-blkg config update. This function must be called on all
- * blkg_conf_ctx's initialized with blkg_conf_init().
- */
-void blkg_conf_exit(struct blkg_conf_ctx *ctx)
+static void __blkg_conf_exit(struct blkg_conf_ctx *ctx)
 	__releases(&ctx->bdev->bd_queue->queue_lock)
 	__releases(&ctx->bdev->bd_queue->rq_qos_mutex)
 {
@@ -986,6 +980,26 @@ void blkg_conf_exit(struct blkg_conf_ctx *ctx)
 		mutex_unlock(&ctx->bdev->bd_queue->rq_qos_mutex);
 		blkdev_put_no_open(ctx->bdev);
 		ctx->body = NULL;
+	}
+}
+
+/**
+ * blkg_conf_exit - clean up per-blkg config update
+ * @ctx: blkg_conf_ctx initialized with blkg_conf_init()
+ *
+ * Clean up after per-blkg config update. This function must be called on all
+ * blkg_conf_ctx's initialized with blkg_conf_init().
+ */
+void blkg_conf_exit(struct blkg_conf_ctx *ctx)
+{
+	__blkg_conf_exit(ctx);
+	if (ctx->bdev) {
+		struct request_queue *q = ctx->bdev->bd_queue;
+
+		mutex_lock(&q->debugfs_mutex);
+		blk_mq_debugfs_register_rq_qos(q);
+		mutex_unlock(&q->debugfs_mutex);
+
 		ctx->bdev = NULL;
 	}
 }
@@ -1000,8 +1014,14 @@ void blkg_conf_exit_frozen(struct blkg_conf_ctx *ctx, unsigned long memflags)
 	if (ctx->bdev) {
 		struct request_queue *q = ctx->bdev->bd_queue;
 
-		blkg_conf_exit(ctx);
+		__blkg_conf_exit(ctx);
 		blk_mq_unfreeze_queue(q, memflags);
+
+		mutex_lock(&q->debugfs_mutex);
+		blk_mq_debugfs_register_rq_qos(q);
+		mutex_unlock(&q->debugfs_mutex);
+
+		ctx->bdev = NULL;
 	}
 }
 
diff --git a/block/blk-rq-qos.c b/block/blk-rq-qos.c
index 654478dfbc20..d7ce99ce2e80 100644
--- a/block/blk-rq-qos.c
+++ b/block/blk-rq-qos.c
@@ -347,13 +347,6 @@ int rq_qos_add(struct rq_qos *rqos, struct gendisk *disk, enum rq_qos_id id,
 	blk_queue_flag_set(QUEUE_FLAG_QOS_ENABLED, q);
 
 	blk_mq_unfreeze_queue(q, memflags);
-
-	if (rqos->ops->debugfs_attrs) {
-		mutex_lock(&q->debugfs_mutex);
-		blk_mq_debugfs_register_rqos(rqos);
-		mutex_unlock(&q->debugfs_mutex);
-	}
-
 	return 0;
 ebusy:
 	blk_mq_unfreeze_queue(q, memflags);
diff --git a/block/blk-sysfs.c b/block/blk-sysfs.c
index 5c2d29ac6570..fb165f2977e6 100644
--- a/block/blk-sysfs.c
+++ b/block/blk-sysfs.c
@@ -722,6 +722,10 @@ static ssize_t queue_wb_lat_store(struct gendisk *disk, const char *page,
 out:
 	blk_mq_unfreeze_queue(q, memflags);
 
+	mutex_lock(&q->debugfs_mutex);
+	blk_mq_debugfs_register_rq_qos(q);
+	mutex_unlock(&q->debugfs_mutex);
+
 	return ret;
 }
 
diff --git a/block/blk-wbt.c b/block/blk-wbt.c
index eb8037bae0bd..b1ab0f297f24 100644
--- a/block/blk-wbt.c
+++ b/block/blk-wbt.c
@@ -724,8 +724,12 @@ void wbt_enable_default(struct gendisk *disk)
 	if (!blk_queue_registered(q))
 		return;
 
-	if (queue_is_mq(q) && enable)
+	if (queue_is_mq(q) && enable) {
 		wbt_init(disk);
+		mutex_lock(&q->debugfs_mutex);
+		blk_mq_debugfs_register_rq_qos(q);
+		mutex_unlock(&q->debugfs_mutex);
+	}
 }
 EXPORT_SYMBOL_GPL(wbt_enable_default);
 
-- 
2.51.0