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

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

[Andy Shevchenko]

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>
---
 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

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

[Simona Vetter]

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>

Reviewed-by: Simona Vetter <simona.vetter@ffwll.ch>

Also ack for the dmem part for merging through your tree.
-Sima

> ---
>  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
> 

-- 
Simona Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch

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

[Paul E. McKenney]

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
>