Re: [PATCH v19 34/40] rcu/update: fix same dept key collision between various types of RCU

[sashiko-bot]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Low] Unused struct member `dkey` inflates stack footprint
--

commit de6aa9797881496b4a8d7d66626b1bfd19cfdd54
Author: Yunseong Kim <ysk@xxxxxxxxxxx>

rcu/update: fix same dept key collision between various types of RCU

This commit addresses a false positive circular dependency report in dept
by assigning separate dept keys and maps to each struct rcu_synchronize
execution context.

> diff --git a/include/linux/rcupdate_wait.h b/include/linux/rcupdate_wait.h
> --- a/include/linux/rcupdate_wait.h
> +++ b/include/linux/rcupdate_wait.h
> @@ -19,17 +19,20 @@ struct rcu_synchronize {
>  
>  	/* This is for debugging. */
>  	struct rcu_gp_oldstate oldstate;
> +	struct dept_map dmap;
> +	struct dept_key dkey;

[Severity: Low]
Does this code ever use the dkey member of struct rcu_synchronize?

The _wait_rcu_gp() macro defines its own static struct dept_key __key,
which it passes as an argument to __wait_rcu_gp(). This leaves the dkey
member of struct rcu_synchronize completely unused and uninitialized, while
needlessly increasing the stack footprint of the rs_array allocated in the
macro.

>  };
>  void wakeme_after_rcu(struct rcu_head *head);
>  
>  void __wait_rcu_gp(bool checktiny, unsigned int state, int n, call_rcu_func_t *crcu_array,
> -		   struct rcu_synchronize *rs_array);
> +		   struct rcu_synchronize *rs_array, struct dept_key *dkey);
>  
>  #define _wait_rcu_gp(checktiny, state, ...) \
> -do {												\
> -	call_rcu_func_t __crcu_array[] = { __VA_ARGS__ };					\
> -	struct rcu_synchronize __rs_array[ARRAY_SIZE(__crcu_array)];				\
> -	__wait_rcu_gp(checktiny, state, ARRAY_SIZE(__crcu_array), __crcu_array, __rs_array);	\
> +do {													\
> +	call_rcu_func_t __crcu_array[] = { __VA_ARGS__ };						\
> +	static struct dept_key __key;									\
> +	struct rcu_synchronize __rs_array[ARRAY_SIZE(__crcu_array)];					\
> +	__wait_rcu_gp(checktiny, state, ARRAY_SIZE(__crcu_array), __crcu_array, __rs_array, &__key);	\
>  } while (0)

[ ... ]

> diff --git a/kernel/rcu/update.c b/kernel/rcu/update.c
> --- a/kernel/rcu/update.c
> +++ b/kernel/rcu/update.c

[ ... ]

> @@ -426,7 +426,8 @@ void __wait_rcu_gp(bool checktiny, unsigned int state, int n, call_rcu_func_t *c
>  				break;
>  		if (j == i) {
>  			init_rcu_head_on_stack(&rs_array[i].head);
> -			init_completion(&rs_array[i].completion);
> +			sdt_map_init_key(&rs_array[i].dmap, dkey);
> +			init_completion_dmap(&rs_array[i].completion, &rs_array[i].dmap);
>  			(crcu_array[i])(&rs_array[i].head, wakeme_after_rcu);
>  		}
>  	}

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260706061928.66713-1-byungchul@xxxxxx?part=34