While del_gendisk ensures there is no outstanding I/O on the queue, it can't prevent block layer users from building new I/O. This leads to a NULL ->root_blkg reference in bio_associate_blkg when allocating a new bio on a shut down file system. Delay freeing the blk-cgroup subsystems from del_gendisk until disk_release to make sure the blkg and throttle information is still avaіlable for bio submitters, even if those bios will immediately fail. This now can cause a case where disk_release is called on a disk that hasn't been added. That's mostly harmless, except for a case in blk_throttl_exit that now needs to check for a NULL ->td pointer. Fixes: 178fa7d49815 ("blk-cgroup: delay blk-cgroup initialization until add_disk") Reported-by: Ming Lei <ming.lei@xxxxxxxxxx> Signed-off-by: Christoph Hellwig <hch@xxxxxx> --- block/blk-throttle.c | 3 ++- block/genhd.c | 4 ++-- 2 files changed, 4 insertions(+), 3 deletions(-) diff --git a/block/blk-throttle.c b/block/blk-throttle.c index 902203bdddb4b4..e7bd7050d68402 100644 --- a/block/blk-throttle.c +++ b/block/blk-throttle.c @@ -2411,7 +2411,8 @@ void blk_throtl_exit(struct gendisk *disk) { struct request_queue *q = disk->queue; - BUG_ON(!q->td); + if (!q->td) + return; del_timer_sync(&q->td->service_queue.pending_timer); throtl_shutdown_wq(q); blkcg_deactivate_policy(disk, &blkcg_policy_throtl); diff --git a/block/genhd.c b/block/genhd.c index 7e031559bf514c..65373738c70b02 100644 --- a/block/genhd.c +++ b/block/genhd.c @@ -668,8 +668,6 @@ void del_gendisk(struct gendisk *disk) rq_qos_exit(q); blk_mq_unquiesce_queue(q); - blkcg_exit_disk(disk); - /* * If the disk does not own the queue, allow using passthrough requests * again. Else leave the queue frozen to fail all I/O. @@ -1166,6 +1164,8 @@ static void disk_release(struct device *dev) might_sleep(); WARN_ON_ONCE(disk_live(disk)); + blkcg_exit_disk(disk); + /* * To undo the all initialization from blk_mq_init_allocated_queue in * case of a probe failure where add_disk is never called we have to -- 2.39.1