[PATCH] list: Remove unnecessary WRITE_ONCE()

[PATCH] list: Remove unnecessary WRITE_ONCE()

[Alan Huang]

Commit c54a2744497d("list: Add hlist_unhashed_lockless()") added
various WRITE_ONCE() to pair with the READ_ONCE() in
hlist_unhashed_lockless(), but there is no need to protect
->next with WRITE_ONCE(). Therefore, this commit removes those
unnecessary WRITE_ONCE().

Signed-off-by: Alan Huang <mmpgouride@gmail.com>
---
 include/linux/list.h | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/include/linux/list.h b/include/linux/list.h
index f10344dbad..ac366958ea 100644
--- a/include/linux/list.h
+++ b/include/linux/list.h
@@ -940,7 +940,7 @@ static inline void hlist_del_init(struct hlist_node *n)
 static inline void hlist_add_head(struct hlist_node *n, struct hlist_head *h)
 {
 	struct hlist_node *first = h->first;
-	WRITE_ONCE(n->next, first);
+	n->next = first;
 	if (first)
 		WRITE_ONCE(first->pprev, &n->next);
 	WRITE_ONCE(h->first, n);
@@ -956,7 +956,7 @@ static inline void hlist_add_before(struct hlist_node *n,
 				    struct hlist_node *next)
 {
 	WRITE_ONCE(n->pprev, next->pprev);
-	WRITE_ONCE(n->next, next);
+	n->next = next;
 	WRITE_ONCE(next->pprev, &n->next);
 	WRITE_ONCE(*(n->pprev), n);
 }
@@ -969,8 +969,8 @@ static inline void hlist_add_before(struct hlist_node *n,
 static inline void hlist_add_behind(struct hlist_node *n,
 				    struct hlist_node *prev)
 {
-	WRITE_ONCE(n->next, prev->next);
-	WRITE_ONCE(prev->next, n);
+	n->next = prev->next;
+	prev->next = n;
 	WRITE_ONCE(n->pprev, &prev->next);
 
 	if (n->next)
-- 
2.34.1

Re: [PATCH] list: Remove unnecessary WRITE_ONCE()

[Eric Dumazet]

On Mon, Jun 19, 2023 at 11:03 AM Alan Huang <mmpgouride@gmail.com> wrote:
>
> Commit c54a2744497d("list: Add hlist_unhashed_lockless()") added
> various WRITE_ONCE() to pair with the READ_ONCE() in
> hlist_unhashed_lockless(), but there is no need to protect
> ->next with WRITE_ONCE(). Therefore, this commit removes those
> unnecessary WRITE_ONCE().

Why are they unnecessary ?
They seem just fine to me.
Please elaborate.

Re: [PATCH] list: Remove unnecessary WRITE_ONCE()

[Alan Huang]

> 2023年6月19日 19:02，Eric Dumazet <edumazet@google.com> 写道：
> 
> On Mon, Jun 19, 2023 at 11:03 AM Alan Huang <mmpgouride@gmail.com> wrote:
>> 
>> Commit c54a2744497d("list: Add hlist_unhashed_lockless()") added
>> various WRITE_ONCE() to pair with the READ_ONCE() in
>> hlist_unhashed_lockless(), but there is no need to protect
>> ->next with WRITE_ONCE(). Therefore, this commit removes those
>> unnecessary WRITE_ONCE().
> 
> Why are they unnecessary ?

There is no reader locklessly read ->next.

These functions are protected by something like spin_lock, only the thread running 
the function can access ->next.

> They seem just fine to me.
> Please elaborate.

Re: [PATCH] list: Remove unnecessary WRITE_ONCE()

[Alan Huang]

Hi Paul,

Looks like you missed this one?

Thanks,
Alan

> 2023年6月19日 17:03，Alan Huang <mmpgouride@gmail.com> 写道：
> 
> Commit c54a2744497d("list: Add hlist_unhashed_lockless()") added
> various WRITE_ONCE() to pair with the READ_ONCE() in
> hlist_unhashed_lockless(), but there is no need to protect
> ->next with WRITE_ONCE(). Therefore, this commit removes those
> unnecessary WRITE_ONCE().
> 
> Signed-off-by: Alan Huang <mmpgouride@gmail.com>
> ---
> include/linux/list.h | 8 ++++----
> 1 file changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/include/linux/list.h b/include/linux/list.h
> index f10344dbad..ac366958ea 100644
> --- a/include/linux/list.h
> +++ b/include/linux/list.h
> @@ -940,7 +940,7 @@ static inline void hlist_del_init(struct hlist_node *n)
> static inline void hlist_add_head(struct hlist_node *n, struct hlist_head *h)
> {
> struct hlist_node *first = h->first;
> - WRITE_ONCE(n->next, first);
> + n->next = first;
> if (first)
> WRITE_ONCE(first->pprev, &n->next);
> WRITE_ONCE(h->first, n);
> @@ -956,7 +956,7 @@ static inline void hlist_add_before(struct hlist_node *n,
>    struct hlist_node *next)
> {
> WRITE_ONCE(n->pprev, next->pprev);
> - WRITE_ONCE(n->next, next);
> + n->next = next;
> WRITE_ONCE(next->pprev, &n->next);
> WRITE_ONCE(*(n->pprev), n);
> }
> @@ -969,8 +969,8 @@ static inline void hlist_add_before(struct hlist_node *n,
> static inline void hlist_add_behind(struct hlist_node *n,
>    struct hlist_node *prev)
> {
> - WRITE_ONCE(n->next, prev->next);
> - WRITE_ONCE(prev->next, n);
> + n->next = prev->next;
> + prev->next = n;
> WRITE_ONCE(n->pprev, &prev->next);
> 
> if (n->next)
> -- 
> 2.34.1
>