Re: [PATCH v3] blk-cgroup: fix leaks and online flag on radix_tree_insert failure

[Tejun Heo <tj@kernel.org>]

On Thu, May 07, 2026 at 02:12:29PM +0800, Tao Cui wrote:
> When radix_tree_insert() fails in blkg_create(), the error path has two
> issues:
> 
> 1. blkg->online is set to true unconditionally, even when the blkg was
>    never fully inserted.  Move the assignment inside the success block.
> 
> 2. The error path calls blkg_put() without first calling
>    percpu_ref_kill().  Because the refcount is still in percpu mode,
>    percpu_ref_put() only does this_cpu_sub() without checking for zero,
>    so blkg_release() is never triggered.  This permanently leaks the
>    blkg memory, its percpu iostat, policy data, the parent blkg
>    reference, and the cgroup css reference — the latter preventing the
>    cgroup from ever being destroyed.
> 
> Fix by replacing blkg_put() with percpu_ref_kill(), matching the pattern
> used in blkg_destroy().
> 
> Signed-off-by: Tao Cui <cuitao@kylinos.cn>

Acked-by: Tejun Heo <tj@kernel.org>

Thanks.

-- 
tejun