Re: [RFC PATCH 1/4] mm/damon/core: handle NULL ctx parameter in damon_call()

[Gutierrez Asier <gutierrez.asier@huawei-partners.com>]

Hi SJ,

On 8/13/2026 6:49 AM, SJ Park wrote:
> When NULL damon_ctx pointer parameter is passed, damon_call() could do
> NULL dereference.  The caller is responsible to avoid that.  It is easy
> to forget, and there are many damon_call() callers.  Meanwhile,
> damon_call() is never meant to be performance critical.  It uses mutex
> and completion.  Add the NULL pointer check inside damon_call() so that
> callers can pass the parameter without NULL checks.
> 
> Signed-off-by: SJ Park <sj@kernel.org>
> ---
>  mm/damon/core.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/mm/damon/core.c b/mm/damon/core.c
> index 92631a36d7b51..5882f9c94c47f 100644
> --- a/mm/damon/core.c
> +++ b/mm/damon/core.c
> @@ -2188,6 +2188,8 @@ int damon_kdamond_pid(struct damon_ctx *ctx)
>   */
>  int damon_call(struct damon_ctx *ctx, struct damon_call_control *control)
>  {
> +	if (!ctx)
> +		return -EINVAL;
>  	if (!control->repeat)
>  		init_completion(&control->completion);
>  	control->canceled = false;

I know that this is a minor optimization, but how about moving INIT_LIST_HEAD(&control->list)
to right before list_add_tail?

It doesn't make sense to initialize the list before checking call_controls_obsolete.

Maybe this suggestion should go in a different patch.

-- 
Asier Gutierrez
Huawei