2020-07-26 11:43:09

by Julia Lawall

Subject: [PATCH 4/7] net/mlx5: drop unnecessary list_empty

list_for_each_entry is able to handle an empty list.
The only effect of avoiding the loop is not initializing the
index variable.
Drop list_empty tests in cases where these variables are not
used.

Note that list_for_each_entry is defined in terms of list_first_entry,
which indicates that it should not be used on an empty list. But in
list_for_each_entry, the element obtained by list_first_entry is not
really accessed, only the address of its list_head field is compared
to the address of the list head, so the list_first_entry is safe.

The semantic patch that makes this change is as follows (with another
variant for the no brace case): (http://coccinelle.lip6.fr/)

<smpl>
@@
expression x,e;
iterator name list_for_each_entry;
statement S;
identifier i;
@@

-if (!(list_empty(x))) {
list_for_each_entry(i,x,...) S
- }
... when != i
? i = e
</smpl>

Signed-off-by: Julia Lawall <[email protected]>

---
drivers/net/ethernet/mellanox/mlx5/core/steering/dr_matcher.c | 13 ++++------
drivers/net/ethernet/mellanox/mlx5/core/steering/dr_rule.c | 5 +--
2 files changed, 8 insertions(+), 10 deletions(-)

diff --git a/drivers/net/ethernet/mellanox/mlx5/core/steering/dr_matcher.c b/drivers/net/ethernet/mellanox/mlx5/core/steering/dr_matcher.c
index 31abcbb..23a1172 100644
--- a/drivers/net/ethernet/mellanox/mlx5/core/steering/dr_matcher.c
+++ b/drivers/net/ethernet/mellanox/mlx5/core/steering/dr_matcher.c
@@ -474,14 +474,13 @@ static int dr_matcher_add_to_tbl(struct mlx5dr_matcher *matcher)
int ret;

next_matcher = NULL;
- if (!list_empty(&tbl->matcher_list))
- list_for_each_entry(tmp_matcher, &tbl->matcher_list, matcher_list) {
- if (tmp_matcher->prio >= matcher->prio) {
- next_matcher = tmp_matcher;
- break;
- }
- first = false;
+ list_for_each_entry(tmp_matcher, &tbl->matcher_list, matcher_list) {
+ if (tmp_matcher->prio >= matcher->prio) {
+ next_matcher = tmp_matcher;
+ break;
}
+ first = false;
+ }

prev_matcher = NULL;
if (next_matcher && !first)
diff --git a/drivers/net/ethernet/mellanox/mlx5/core/steering/dr_rule.c b/drivers/net/ethernet/mellanox/mlx5/core/steering/dr_rule.c
index cd708dc..6ec5106 100644
--- a/drivers/net/ethernet/mellanox/mlx5/core/steering/dr_rule.c
+++ b/drivers/net/ethernet/mellanox/mlx5/core/steering/dr_rule.c
@@ -574,9 +574,8 @@ void mlx5dr_rule_update_rule_member(struct mlx5dr_ste *ste,
{
struct mlx5dr_rule_member *rule_mem;

- if (!list_empty(&ste->rule_list))
- list_for_each_entry(rule_mem, &ste->rule_list, use_ste_list)
- rule_mem->ste = new_ste;
+ list_for_each_entry(rule_mem, &ste->rule_list, use_ste_list)
+ rule_mem->ste = new_ste;
}

static void dr_rule_clean_rule_members(struct mlx5dr_rule *rule,

2020-07-27 18:56:02

by David Miller

Subject: Re: [PATCH 4/7] net/mlx5: drop unnecessary list_empty

From: Julia Lawall <[email protected]>
Date: Sun, 26 Jul 2020 12:58:29 +0200

> list_for_each_entry is able to handle an empty list.
> The only effect of avoiding the loop is not initializing the
> index variable.
> Drop list_empty tests in cases where these variables are not
> used.
>
> Note that list_for_each_entry is defined in terms of list_first_entry,
> which indicates that it should not be used on an empty list. But in
> list_for_each_entry, the element obtained by list_first_entry is not
> really accessed, only the address of its list_head field is compared
> to the address of the list head, so the list_first_entry is safe.
>
> The semantic patch that makes this change is as follows (with another
> variant for the no brace case): (http://coccinelle.lip6.fr/)
...
> Signed-off-by: Julia Lawall <[email protected]>

Saeed, please pick this up.

Thank you.

2020-07-28 07:55:33

by Saeed Mahameed

Subject: Re: [PATCH 4/7] net/mlx5: drop unnecessary list_empty

On Mon, 2020-07-27 at 10:10 -0700, David Miller wrote:
> From: Julia Lawall <[email protected]>
> Date: Sun, 26 Jul 2020 12:58:29 +0200
>
> > list_for_each_entry is able to handle an empty list.
> > The only effect of avoiding the loop is not initializing the
> > index variable.
> > Drop list_empty tests in cases where these variables are not
> > used.
> >
> > Note that list_for_each_entry is defined in terms of
> list_first_entry,
> > which indicates that it should not be used on an empty list. But
> in
> > list_for_each_entry, the element obtained by list_first_entry is
> not
> > really accessed, only the address of its list_head field is
> compared
> > to the address of the list head, so the list_first_entry is safe.
> >
> > The semantic patch that makes this change is as follows (with
> another
> > variant for the no brace case): (http://coccinelle.lip6.fr/)
> ...
> > Signed-off-by: Julia Lawall <[email protected]>
>
> Saeed, please pick this up.
>
> Thank you.

Applied to net-next-mlx5.

Thanks !