Re: [PATCH v1 1/1] rculist: move list_for_each_rcu() to where it belongs

["Paul E. McKenney" <paulmck@kernel.org>]

On Thu, Jul 10, 2025 at 03:15:28PM +0300, Andy Shevchenko wrote:
> The list_for_each_rcu() relies on the rcu_dereference() API which is not
> provided by the list.h. At the same time list.h is a low-level basic header
> that must not have dependencies like RCU, besides the fact of the potential
> circular dependencies in some cases. With all that said, move RCU related
> API to the rculist.h where it belongs.
> 
> Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>

I cannot see why this would not work, and it does pass testing, but I
am adding David Howells in case there is some subtle reason why this
must remain in include/linux/list.h.

ad25f5cb3987 ("rxrpc: Fix locking issue")

In the absence of such a reason, from an RCU viewpoint:

Reviewed-by: Paul E. McKenney <paulmck@kernel.org>

> ---
>  include/linux/list.h    | 10 ----------
>  include/linux/rculist.h | 10 ++++++++++
>  kernel/cgroup/dmem.c    |  1 +
>  3 files changed, 11 insertions(+), 10 deletions(-)
> 
> diff --git a/include/linux/list.h b/include/linux/list.h
> index e7e28afd28f8..e7bdad9b8618 100644
> --- a/include/linux/list.h
> +++ b/include/linux/list.h
> @@ -686,16 +686,6 @@ static inline void list_splice_tail_init(struct list_head *list,
>  #define list_for_each(pos, head) \
>  	for (pos = (head)->next; !list_is_head(pos, (head)); pos = pos->next)
>  
> -/**
> - * list_for_each_rcu - Iterate over a list in an RCU-safe fashion
> - * @pos:	the &struct list_head to use as a loop cursor.
> - * @head:	the head for your list.
> - */
> -#define list_for_each_rcu(pos, head)		  \
> -	for (pos = rcu_dereference((head)->next); \
> -	     !list_is_head(pos, (head)); \
> -	     pos = rcu_dereference(pos->next))
> -
>  /**
>   * list_for_each_continue - continue iteration over a list
>   * @pos:	the &struct list_head to use as a loop cursor.
> diff --git a/include/linux/rculist.h b/include/linux/rculist.h
> index 1b11926ddd47..2abba7552605 100644
> --- a/include/linux/rculist.h
> +++ b/include/linux/rculist.h
> @@ -42,6 +42,16 @@ static inline void INIT_LIST_HEAD_RCU(struct list_head *list)
>   */
>  #define list_bidir_prev_rcu(list) (*((struct list_head __rcu **)(&(list)->prev)))
>  
> +/**
> + * list_for_each_rcu - Iterate over a list in an RCU-safe fashion
> + * @pos:	the &struct list_head to use as a loop cursor.
> + * @head:	the head for your list.
> + */
> +#define list_for_each_rcu(pos, head)		  \
> +	for (pos = rcu_dereference((head)->next); \
> +	     !list_is_head(pos, (head)); \
> +	     pos = rcu_dereference(pos->next))
> +
>  /**
>   * list_tail_rcu - returns the prev pointer of the head of the list
>   * @head: the head of the list
> diff --git a/kernel/cgroup/dmem.c b/kernel/cgroup/dmem.c
> index 10b63433f057..e12b946278b6 100644
> --- a/kernel/cgroup/dmem.c
> +++ b/kernel/cgroup/dmem.c
> @@ -14,6 +14,7 @@
>  #include <linux/mutex.h>
>  #include <linux/page_counter.h>
>  #include <linux/parser.h>
> +#include <linux/rculist.h>
>  #include <linux/slab.h>
>  
>  struct dmem_cgroup_region {
> -- 
> 2.47.2
>