From 3c17a346ffc613615f48c6f1ed30cdf328bab805 Mon Sep 17 00:00:00 2001 From: Yu Kuai Date: Mon, 2 Feb 2026 16:05:19 +0800 Subject: [PATCH] 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 Reviewed-by: Nilay Shroff Reviewed-by: Ming Lei Reviewed-by: Hannes Reinecke Signed-off-by: Jens Axboe --- block/blk-rq-qos.c | 7 ------- block/blk-wbt.c | 13 ++++++++++++- 2 files changed, 12 insertions(+), 8 deletions(-) diff --git a/block/blk-rq-qos.c b/block/blk-rq-qos.c index 654478dfbc204..d7ce99ce2e808 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-wbt.c b/block/blk-wbt.c index 665760274e601..1415f2bf86116 100644 --- 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; } -- 2.47.3