2023-06-19 09:35:54

by Alan Huang

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

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 <[email protected]>
---
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

2023-06-19 11:29:11

by Eric Dumazet

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

On Mon, Jun 19, 2023 at 11:03 AM Alan Huang <[email protected]> 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.

2023-06-19 11:53:07

by Alan Huang

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

> 2023年6月19日 19:02，Eric Dumazet <[email protected]> 写道：
>
> On Mon, Jun 19, 2023 at 11:03 AM Alan Huang <[email protected]> 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.

2023-06-21 12:27:10

by Alan Huang

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

Hi Paul,

Looks like you missed this one?

Thanks,
Alan

> 2023年6月19日 17:03，Alan Huang <[email protected]> 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 <[email protected]>
> ---
> 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
>