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blk-cgroup: delay calling blkcg_exit_disk until disk_release 

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: 178fa7d498 ("blk-cgroup: delay blk-cgroup initialization until add_disk")
Reported-by: Ming Lei <ming.lei@redhat.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Ming Lei <ming.lei@redhat.com>
Link: https://lore.kernel.org/r/20230208063514.171485-1-hch@lst.de
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Christoph Hellwig 2023-02-08 07:35:14 +01:00 committed by Jens Axboe
parent a872818f48
commit c43332fe02
2 changed files with 4 additions and 3 deletions
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3
block/blk-throttle.c
View File

@ -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);

4
block/genhd.c
View File

@ -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