Re: [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:

Pre-existing issues:
- [High] The patch correctly fixes an indefinite wait vulnerability in damon_call() by initializing ctx->call_controls_obsolete to true, but fails to initialize the identical ctx->walk_control_obsolete flag. This leaves damos_walk() vulnerable to the exact same indefinite hang if called on an unstarted context.
--

commit 55412502962e64df1de83b2c9805595450e93fc7
Author: SJ Park <sj@kernel.org>

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

This patch sets ctx->call_controls_obsolete to true in damon_new_ctx() to
prevent indefinite hangs when damon_call() is used on an unstarted context.

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

> diff --git a/mm/damon/core.c b/mm/damon/core.c
> index f1f007d8dd1d9..610556abb129e 100644
> --- a/mm/damon/core.c
> +++ b/mm/damon/core.c
> @@ -933,6 +933,7 @@ struct damon_ctx *damon_new_ctx(void)
>  	INIT_LIST_HEAD(&ctx->adaptive_targets);
>  	INIT_LIST_HEAD(&ctx->schemes);
>  
> +	ctx->call_controls_obsolete = true;

[Severity: High]
This is a pre-existing issue, but does the same fix need to be applied to
ctx->walk_control_obsolete?

Because walk_control_obsolete is zero-initialized (false) by kzalloc_obj(),
calling damos_walk() on an unstarted context will bypass the obsolete check:

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

This could lead to an indefinite hang in wait_for_completion(), since the
DAMON worker thread is not running to signal the completion. Should
ctx->walk_control_obsolete also be initialized to true here?

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

[ ... ]

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Sashiko AI review · https://sashiko.dev/#/patchset/20260903010334.93622-1-sj@kernel.org?part=2