Re: [RFC PATCH 2/4] mm/damon/core: set ctx->call_controls_obsolete in damon_new_ctx()

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Medium] The patch introduces an inconsistent state in the `damon_ctx` API by initializing `call_controls_obsolete` to true while leaving its identically-designed sibling field `walk_control_obsolete` as false.
--

--- Patch [2]: [RFC PATCH 2/4] mm/damon/core: set ctx->call_controls_obsolete in damon_new_ctx() ---
commit 94c12d6bfcca8f83b408960a36d0c0a8519d80c7
Author: SJ Park <sj@kernel.org>

mm/damon/core: set ctx->call_controls_obsolete in damon_new_ctx()

This commit addresses an issue where passing an unstarted DAMON context
to damon_call() can cause an indefinite hang. It fixes this by initializing
ctx->call_controls_obsolete to true in damon_new_ctx().

Link: https://lore.kernel.org/20260803134646.16640-1-sj@kernel.org

> diff --git a/mm/damon/core.c b/mm/damon/core.c
> index af7b77710745d..5080cb12220d2 100644
> --- a/mm/damon/core.c
> +++ b/mm/damon/core.c
> @@ -864,6 +864,7 @@ struct damon_ctx *damon_new_ctx(void)
>  	INIT_LIST_HEAD(&ctx->adaptive_targets);
>  	INIT_LIST_HEAD(&ctx->schemes);
>  
> +	ctx->call_controls_obsolete = true;

[Severity: Medium]
Should ctx->walk_control_obsolete also be initialized to true here?

Because walk_control_obsolete is zero-initialized to false during allocation,
an unstarted context passed to damos_walk() will bypass the obsolete check:

mm/damon/core.c:damos_walk() {
	...
	if (ctx->walk_control_obsolete) {
		mutex_unlock(&ctx->walk_control_lock);
		return -ECANCELED;
	}
	...
}

This appears to leave damos_walk() vulnerable to the exact same indefinite
wait_for_completion() hang on unstarted contexts that this patch resolves for
damon_call(). 

Does it make sense to update walk_control_obsolete alongside
call_controls_obsolete to ensure the API behaves consistently?

>  	prandom_seed_state(&ctx->rnd_state, get_random_u64());
>  
>  	return ctx;

[ ... ]

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260813035001.97364-1-sj@kernel.org?part=2