Re: [PATCH] mm/damon/core: reset invalid quota->charge_target_from

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:

Pre-existing issues:
- [High] The newly added fix for invalid `charge_target_from` pointers is bypassed if a scheme's quota is dynamically disabled, leaving the scheme permanently broken.
--

commit f88287bb2670346a5987d086e0731c7ba6d0b19e
Author: SJ Park <sj@kernel.org>

    mm/damon/core: reset invalid quota->charge_target_from
    
    DAMOS can suddenly stop working if a target process that quota just
    fully charged in it is terminated.  Fix by catching and processing the
    corner case.

> diff --git a/mm/damon/core.c b/mm/damon/core.c
> index ce8c6f99106ed..2c58be9edbde4 100644
> --- a/mm/damon/core.c
> +++ b/mm/damon/core.c
[ ... ]
> @@ -3318,6 +3334,8 @@ static void damos_adjust_quota(struct damon_ctx *c, struct damos *s)
>  			damos_trace_esz(c, s, quota);
>  	}
>  
> +	damos_reset_invalid_charge_target_from(quota, c);
> +
>  	if (!c->ops.get_scheme_score)
>  		return;
>  

[Severity: High]
This is a pre-existing issue, but does this bypass the newly added reset if a
scheme's quota is dynamically disabled?

If a user hits the corner case where charge_target_from becomes invalid, and
then dynamically disables the scheme's quota via sysfs (setting ms=0 and
sz=0), damos_adjust_quota() will return early before the reset is reached:

mm/damon/core.c:damos_adjust_quota() {
	if (!quota->ms && !quota->sz && list_empty(&quota->goals))
		return;
	...
}

Because damos_skip_charged_region() does not check if the quota is enabled
before evaluating charge_target_from, it will continue to skip all regions
forever:

mm/damon/core.c:damos_skip_charged_region() {
	...
		if (t != quota->charge_target_from)
			return true;
	...
}

Could the pointer reset be moved before the early return in
damos_adjust_quota(), or could the skipping logic be updated to handle
disabled quotas?

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260907165529.98874-1-sj@kernel.org?part=1