[RFC,05/21] list: Comment missing WRITE_ONCE() in __list_del()
diff mbox series

Message ID 20200324153643.15527-6-will@kernel.org
State New
Headers show
Series
  • Improve list integrity checking
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Commit Message

Will Deacon March 24, 2020, 3:36 p.m. UTC
Although __list_del() is called from the RCU list implementation, it
omits WRITE_ONCE() when updating the 'prev' pointer for the 'next' node.
This is reasonable because concurrent RCU readers only access the 'next'
pointers.

Although it's obvious after reading the code, add a comment.

Cc: Paul E. McKenney <paulmck@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Will Deacon <will@kernel.org>
---
 include/linux/list.h | 1 +
 1 file changed, 1 insertion(+)

Comments

Paul E. McKenney March 30, 2020, 11:14 p.m. UTC | #1
On Tue, Mar 24, 2020 at 03:36:27PM +0000, Will Deacon wrote:
> Although __list_del() is called from the RCU list implementation, it
> omits WRITE_ONCE() when updating the 'prev' pointer for the 'next' node.
> This is reasonable because concurrent RCU readers only access the 'next'
> pointers.
> 
> Although it's obvious after reading the code, add a comment.
> 
> Cc: Paul E. McKenney <paulmck@kernel.org>
> Cc: Peter Zijlstra <peterz@infradead.org>
> Signed-off-by: Will Deacon <will@kernel.org>

OK, I will take the easy one.  ;-)

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

> ---
>  include/linux/list.h | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/include/linux/list.h b/include/linux/list.h
> index 4d9f5f9ed1a8..ec1f780d1449 100644
> --- a/include/linux/list.h
> +++ b/include/linux/list.h
> @@ -109,6 +109,7 @@ static inline void list_add_tail(struct list_head *new, struct list_head *head)
>   */
>  static inline void __list_del(struct list_head * prev, struct list_head * next)
>  {
> +	/* RCU readers don't read the 'prev' pointer */
>  	next->prev = prev;
>  	WRITE_ONCE(prev->next, next);
>  }
> -- 
> 2.20.1
>

Patch
diff mbox series

diff --git a/include/linux/list.h b/include/linux/list.h
index 4d9f5f9ed1a8..ec1f780d1449 100644
--- a/include/linux/list.h
+++ b/include/linux/list.h
@@ -109,6 +109,7 @@  static inline void list_add_tail(struct list_head *new, struct list_head *head)
  */
 static inline void __list_del(struct list_head * prev, struct list_head * next)
 {
+	/* RCU readers don't read the 'prev' pointer */
 	next->prev = prev;
 	WRITE_ONCE(prev->next, next);
 }