[PATCH 0/7] drop unnecessary list_empty

[PATCH 0/7] drop unnecessary list_empty

[Julia Lawall]

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

The semantic patch that makes these changes is as follows:
(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

@@
expression x,e;
iterator name list_for_each_entry_safe;
statement S;
identifier i,j;
@@

-if (!(list_empty(x))) {
   list_for_each_entry_safe(i,j,x,...) S
- }
 ... when != i
     when != j
(
  i = e;
|
? j = e;
)

@@
expression x,e;
iterator name list_for_each;
statement S;
identifier i;
@@

-if (!(list_empty(x))) {
   list_for_each(i,x) S
- }
 ... when != i
? i = e

@@
expression x,e;
iterator name list_for_each_safe;
statement S;
identifier i,j;
@@

-if (!(list_empty(x))) {
   list_for_each_safe(i,j,x) S
- }
 ... when != i
     when != j
(
  i = e;
|
? j = e;
)

// -------------------

@@
expression x,e;
statement S;
identifier i;
@@

-if (!(list_empty(x)))
   list_for_each_entry(i,x,...) S
 ... when != i
? i = e

@@
expression x,e;
statement S;
identifier i,j;
@@

-if (!(list_empty(x)))
   list_for_each_entry_safe(i,j,x,...) S
 ... when != i
     when != j
(
  i = e;
|
? j = e;
)

@@
expression x,e;
statement S;
identifier i;
@@

-if (!(list_empty(x)))
   list_for_each(i,x) S
 ... when != i
? i = e

@@
expression x,e;
statement S;
identifier i,j;
@@

-if (!(list_empty(x)))
   list_for_each_safe(i,j,x) S
 ... when != i
     when != j
(
  i = e;
|
? j = e;
)
</smpl>

---

 drivers/media/pci/saa7134/saa7134-core.c                      |   14 ++---
 drivers/media/usb/cx231xx/cx231xx-core.c                      |   16 ++----
 drivers/media/usb/tm6000/tm6000-core.c                        |   24 +++-------
 drivers/net/ethernet/mellanox/mlx5/core/steering/dr_matcher.c |   13 ++---
 drivers/net/ethernet/mellanox/mlx5/core/steering/dr_rule.c    |    5 --
 drivers/net/ethernet/sfc/ptp.c                                |   20 +++-----
 drivers/net/wireless/ath/dfs_pattern_detector.c               |   15 ++----
 sound/soc/intel/atom/sst/sst_loader.c                         |   10 +---
 sound/soc/intel/skylake/skl-pcm.c                             |    8 +--
 sound/soc/intel/skylake/skl-topology.c                        |    5 --
 10 files changed, 53 insertions(+), 77 deletions(-)

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

[Julia Lawall]

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 <Julia.Lawall@inria.fr>

---
 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,

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

[David Miller]

From: Julia Lawall <Julia.Lawall@inria.fr>
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 <Julia.Lawall@inria.fr>

Saeed, please pick this up.

Thank you.

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

[Saeed Mahameed]

On Mon, 2020-07-27 at 10:10 -0700, David Miller wrote:
> From: Julia Lawall <Julia.Lawall@inria.fr>
> 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 <Julia.Lawall@inria.fr>
> 
> Saeed, please pick this up.
> 
> Thank you.

Applied to net-next-mlx5.

Thanks !

Re: [PATCH 0/7] drop unnecessary list_empty

[Mark Brown]

On Sun, 26 Jul 2020 12:58:25 +0200, Julia Lawall wrote:
> The various list iterators are able to handle an empty list.
> The only effect of avoiding the loop is not initializing some
> index variables.
> Drop list_empty tests in cases where these variables are not
> used.
> 
> The semantic patch that makes these changes is as follows:
> (http://coccinelle.lip6.fr/)
> 
> [...]

Applied to

   https://git.kernel.org/pub/scm/linux/kernel/git/broonie/sound.git for-next

Thanks!

[1/1] ASoC: Intel: drop unnecessary list_empty
      commit: a383308e50244a28fe927b9c1acbe0a963bf186b

All being well this means that it will be integrated into the linux-next
tree (usually sometime in the next 24 hours) and sent to Linus during
the next merge window (or sooner if it is a bug fix), however if
problems are discovered then the patch may be dropped or reverted.

You may get further e-mails resulting from automated or manual testing
and review of the tree, please engage with people reporting problems and
send followup patches addressing any issues that are reported if needed.

If any updates are required or you are submitting further changes they
should be sent as incremental updates against current git, existing
patches will not be replaced.

Please add any relevant lists and maintainers to the CCs when replying
to this mail.

Thanks,
Mark