blk-rq-qos: fix possible debugfs_mutex deadlock

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_init_enable_default(); 2) it can be
  initialized by sysfs, fix it by calling new helper after queue is
  unfrozen from wbt_set_lat().
- For iocost and iolatency, they can only be initialized by blkcg
  configuration, however, they don't have debugfs entries for now, hence
  they are not handled yet.

Signed-off-by: Yu Kuai <yukuai@fnnas.com>
Reviewed-by: Nilay Shroff <nilay@linux.ibm.com>
Reviewed-by: Ming Lei <ming.lei@redhat.com>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/block/blk-rq-qos.c b/block/blk-rq-qos.c
index 654478dfbc20445914c43416344d8e44adfa9e43..d7ce99ce2e808182ace9d0ae1c6c58b14b55fdb9 100644 (file)
--- 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-wbt.c b/block/blk-wbt.c
index 665760274e601d8ba840e68810db098e9c19f1ab..1415f2bf86116953a59e8c31ad3a8928a01ef2ad 100644 (file)
--- a/block/blk-wbt.c
+++ b/block/blk-wbt.c
@@ -774,6 +774,7 @@ EXPORT_SYMBOL_GPL(wbt_enable_default);
 
 void wbt_init_enable_default(struct gendisk *disk)
 {
+       struct request_queue *q = disk->queue;
        struct rq_wb *rwb;
 
        if (!__wbt_enable_default(disk))
@@ -783,8 +784,14 @@ void wbt_init_enable_default(struct gendisk *disk)
        if (WARN_ON_ONCE(!rwb))
                return;
 
-       if (WARN_ON_ONCE(wbt_init(disk, rwb)))
+       if (WARN_ON_ONCE(wbt_init(disk, rwb))) {
                wbt_free(rwb);
+               return;
+       }
+
+       mutex_lock(&q->debugfs_mutex);
+       blk_mq_debugfs_register_rq_qos(q);
+       mutex_unlock(&q->debugfs_mutex);
 }
 
 static u64 wbt_default_latency_nsec(struct request_queue *q)
@@ -1008,5 +1015,9 @@ int wbt_set_lat(struct gendisk *disk, s64 val)
        blk_mq_unquiesce_queue(q);
 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;
 }