Re: [PATCH v6 1/3] blk-cgroup: Correctly free percpu iostat_cpu in blkg on error exit

[Ming Lei]

On Thu, Jun 02, 2022 at 03:20:18PM -0400, Waiman Long wrote:
> Commit f73316482977 ("blk-cgroup: reimplement basic IO stats using cgroup
> rstat") changes block cgroup IO stats to use the rstat APIs. It added
> a new percpu iostat_cpu field into blkg. The blkg_alloc() was modified
> to allocate the new percpu iostat_cpu but didn't free it when an error
> happened. Fix this by freeing the percpu iostat_cpu on error exit.
> 
> Fixes: f73316482977 ("blk-cgroup: reimplement basic IO stats using cgroup rstat")
> Signed-off-by: Waiman Long <longman@xxxxxxxxxx>
> Acked-by: Tejun Heo <tj@xxxxxxxxxx>
> ---
>  block/blk-cgroup.c | 7 +++++--
>  1 file changed, 5 insertions(+), 2 deletions(-)
> 
> diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c
> index 40161a3f68d0..acd9b0aa8dc8 100644
> --- a/block/blk-cgroup.c
> +++ b/block/blk-cgroup.c
> @@ -219,11 +219,11 @@ static struct blkcg_gq *blkg_alloc(struct blkcg *blkcg, struct request_queue *q,
>  		return NULL;
>  
>  	if (percpu_ref_init(&blkg->refcnt, blkg_release, 0, gfp_mask))
> -		goto err_free;
> +		goto err_free_blkg;
>  
>  	blkg->iostat_cpu = alloc_percpu_gfp(struct blkg_iostat_set, gfp_mask);
>  	if (!blkg->iostat_cpu)
> -		goto err_free;
> +		goto err_free_blkg;
>  
>  	if (!blk_get_queue(q))
>  		goto err_free;
> @@ -259,6 +259,9 @@ static struct blkcg_gq *blkg_alloc(struct blkcg *blkcg, struct request_queue *q,
>  	return blkg;
>  
>  err_free:
> +	free_percpu(blkg->iostat_cpu);
> +
> +err_free_blkg:
>  	blkg_free(blkg);

Hi Waiman,

But blkg_free() frees blkg->iostat_cpu via blkg_free_workfn(), so I am
confused where the leak is in failure path?


Thanks
Ming