Re: [RFC PATCH v1.2 1/2] mm/damon/stat: add a parameter for reading kdamond pid

[sashiko-bot@kernel.org]

Sashiko AI review found 1 potential issue(s):
- [Medium] Stale `kdamond_pid` exposed to userspace if `damon_call()` fails during startup.
--

commit 46eb0a4278ccd2dec190db28b78b0766b8865901
Author: SeongJae Park <sj@kernel.org>

mm/damon/stat: add a parameter for reading kdamond pid

This commit exposes the pid of the DAMON_STAT kdamond via a new read-only
module parameter named kdamond_pid, standardizing usage with other DAMON
modules.

> diff --git a/mm/damon/stat.c b/mm/damon/stat.c
> index 99ba346f9e325..4901e9a7c3398 100644
> --- a/mm/damon/stat.c
> +++ b/mm/damon/stat.c

[ ... ]

> @@ -260,6 +269,14 @@ static int damon_stat_start(void)
>  		damon_stat_context = NULL;
>  		return err;
>  	}
> +	kdamond_pid = damon_kdamond_pid(damon_stat_context);
> +	if (kdamond_pid < 0) {
> +		err = kdamond_pid;
> +		kdamond_pid = -1;
> +		damon_destroy_ctx(damon_stat_context);
> +		damon_stat_context = NULL;
> +		return err;
> +	}
>  
>  	damon_stat_last_refresh_jiffies = jiffies;
>  	call_control.data = damon_stat_context;

If damon_call() fails right after this and returns an error,
damon_stat_start() will pass that error back to its caller and the module
will revert to a disabled state.

Does this leave a stale kdamond_pid exposed to userspace? The newly added
documentation states: "If DAMON_STAT is enabled, this becomes the PID of
the worker thread. Else, -1." Since the initialization fails, the module
remains disabled, but kdamond_pid isn't reset to -1 on this error path.

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260416002149.87090-1-sj@kernel.org?part=1