Re: [PATCH] blk-cgroup: clear blkg->pd[] with WRITE_ONCE() in blkcg_deactivate_policy()

[Tao Cui]

在 2026/7/7 20:58, Guopeng Zhang 写道:
> From: Guopeng Zhang <zhangguopeng@xxxxxxxxxx>
> 
> blkcg_activate_policy() installs blkg->pd[] entries with WRITE_ONCE()
> and also uses WRITE_ONCE() when clearing them on its error path.
> blkg_to_pd() is used by RCU readers and reads the same array with
> READ_ONCE().
> 
> blkcg_deactivate_policy() clears the entry with a plain store. Use
> WRITE_ONCE() there as well.
> 
> Fixes: 56cc24f59c14 ("blk-cgroup: don't nest queue_lock under rcu in blkcg_print_blkgs()")
> Signed-off-by: Guopeng Zhang <zhangguopeng@xxxxxxxxxx>
> ---
>  block/blk-cgroup.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c
> index d2a1f5903f24..a1dd69f99f5c 100644
> --- a/block/blk-cgroup.c
> +++ b/block/blk-cgroup.c
> @@ -1691,7 +1691,7 @@ void blkcg_deactivate_policy(struct gendisk *disk,
>  			if (blkg->pd[pol->plid]->online && pol->pd_offline_fn)
>  				pol->pd_offline_fn(blkg->pd[pol->plid]);
>  			pol->pd_free_fn(blkg->pd[pol->plid]);
> -			blkg->pd[pol->plid] = NULL;
> +			WRITE_ONCE(blkg->pd[pol->plid], NULL);
>  		}
>  		spin_unlock(&blkcg->lock);
>  	}

Reviewed-by: Tao Cui <cuitao@xxxxxxxxxx>