Re: [PATCH] Remove blkg node after destroying blkg

[Yu Kuai]

Hi,

在 2023/04/25 15:59, Tao Su 写道:
> Kernel hang when poweroff or reboot, due to infinite restart in function
> blkg_destroy_all. It will goto restart label when a batch of blkgs are
> destroyed, but not remove blkg node in blkg_list. So the blkg_list is
> same in every 'restart' and result in kernel hang.
>
> By adding list_del to remove blkg node after destroying, can solve this
> kernel hang issue and satisfy the previous will to 'restart'.
>
> Reported-by: Xiangfei Ma <xiangfeix.ma@xxxxxxxxx>
> Tested-by: Xiangfei Ma <xiangfeix.ma@xxxxxxxxx>
> Tested-by: Farrah Chen <farrah.chen@xxxxxxxxx>
> Signed-off-by: Tao Su <tao1.su@xxxxxxxxxxxxxxx>
> ---
>   block/blk-cgroup.c | 1 +
>   1 file changed, 1 insertion(+)
>
> diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c
> index bd50b55bdb61..960eb538a704 100644
> --- a/block/blk-cgroup.c
> +++ b/block/blk-cgroup.c
> @@ -530,6 +530,7 @@ static void blkg_destroy_all(struct gendisk *disk)
>   
>   		spin_lock(&blkcg->lock);
>   		blkg_destroy(blkg);
> +		list_del(&blkg->q_node);

blkg should stay on the queue list until blkg_free_workfn(), otherwise
parent blkg can be freed before child, which will cause some known
issue.

I think this hung happens when total blkg is greater than
BLKG_DESTROY_BATCH_SIZE, right?

Can you try if following patch fix your problem?

index 1c1ebeb51003..0ecb4cce8af2 100644
--- a/block/blk-cgroup.c
+++ b/block/blk-cgroup.c
@@ -527,6 +527,9 @@ static void blkg_destroy_all(struct gendisk *disk)
        list_for_each_entry_safe(blkg, n, &q->blkg_list, q_node) {
                struct blkcg *blkcg = blkg->blkcg;

+               if (hlist_unhashed(&blkg->blkcg_node))
+                       continue;
+
                spin_lock(&blkcg->lock);
                blkg_destroy(blkg);
                spin_unlock(&blkcg->lock);

>   		spin_unlock(&blkcg->lock);
>   
>   		/*