[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 3/7] [media] cx231xx: 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:
(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/media/usb/cx231xx/cx231xx-core.c |   16 ++++++----------
 1 file changed, 6 insertions(+), 10 deletions(-)

diff --git a/drivers/media/usb/cx231xx/cx231xx-core.c b/drivers/media/usb/cx231xx/cx231xx-core.c
index 982cb56e..05d91ca 100644
--- a/drivers/media/usb/cx231xx/cx231xx-core.c
+++ b/drivers/media/usb/cx231xx/cx231xx-core.c
@@ -115,11 +115,9 @@ void cx231xx_init_extension(struct cx231xx *dev)
 	struct cx231xx_ops *ops = NULL;
 
 	mutex_lock(&cx231xx_devlist_mutex);
-	if (!list_empty(&cx231xx_extension_devlist)) {
-		list_for_each_entry(ops, &cx231xx_extension_devlist, next) {
-			if (ops->init)
-				ops->init(dev);
-		}
+	list_for_each_entry(ops, &cx231xx_extension_devlist, next) {
+		if (ops->init)
+			ops->init(dev);
 	}
 	mutex_unlock(&cx231xx_devlist_mutex);
 }
@@ -129,11 +127,9 @@ void cx231xx_close_extension(struct cx231xx *dev)
 	struct cx231xx_ops *ops = NULL;
 
 	mutex_lock(&cx231xx_devlist_mutex);
-	if (!list_empty(&cx231xx_extension_devlist)) {
-		list_for_each_entry(ops, &cx231xx_extension_devlist, next) {
-			if (ops->fini)
-				ops->fini(dev);
-		}
+	list_for_each_entry(ops, &cx231xx_extension_devlist, next) {
+		if (ops->fini)
+			ops->fini(dev);
 	}
 	mutex_unlock(&cx231xx_devlist_mutex);
 }

[PATCH 5/7] [media] saa7134: drop unnecessary list_empty

[Julia Lawall]

list_for_each_safe 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.

The semantic patch that makes this change is as follows:
(http://coccinelle.lip6.fr/)

<smpl>
@@
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;
)
</smpl>

Signed-off-by: Julia Lawall <Julia.Lawall@inria.fr>

---
 drivers/media/pci/saa7134/saa7134-core.c |   14 ++++++--------
 1 file changed, 6 insertions(+), 8 deletions(-)

diff --git a/drivers/media/pci/saa7134/saa7134-core.c b/drivers/media/pci/saa7134/saa7134-core.c
index e4623ed..5095f25 100644
--- a/drivers/media/pci/saa7134/saa7134-core.c
+++ b/drivers/media/pci/saa7134/saa7134-core.c
@@ -359,14 +359,12 @@ void saa7134_stop_streaming(struct saa7134_dev *dev, struct saa7134_dmaqueue *q)
 	struct saa7134_buf *tmp;
 
 	spin_lock_irqsave(&dev->slock, flags);
-	if (!list_empty(&q->queue)) {
-		list_for_each_safe(pos, n, &q->queue) {
-			 tmp = list_entry(pos, struct saa7134_buf, entry);
-			 vb2_buffer_done(&tmp->vb2.vb2_buf,
-					 VB2_BUF_STATE_ERROR);
-			 list_del(pos);
-			 tmp = NULL;
-		}
+	list_for_each_safe(pos, n, &q->queue) {
+		tmp = list_entry(pos, struct saa7134_buf, entry);
+		vb2_buffer_done(&tmp->vb2.vb2_buf,
+				VB2_BUF_STATE_ERROR);
+		list_del(pos);
+		tmp = NULL;
 	}
 	spin_unlock_irqrestore(&dev->slock, flags);
 	saa7134_buffer_timeout(&q->timeout); /* also calls del_timer(&q->timeout) */

[PATCH 6/7] [media] tm6000: 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:
(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/media/usb/tm6000/tm6000-core.c |   24 +++++++++---------------
 1 file changed, 9 insertions(+), 15 deletions(-)

diff --git a/drivers/media/usb/tm6000/tm6000-core.c b/drivers/media/usb/tm6000/tm6000-core.c
index 2c72370..5c8cbc5 100644
--- a/drivers/media/usb/tm6000/tm6000-core.c
+++ b/drivers/media/usb/tm6000/tm6000-core.c
@@ -853,11 +853,9 @@ int tm6000_call_fillbuf(struct tm6000_core *dev, enum tm6000_ops_type type,
 
 	/* FIXME: tm6000_extension_devlist_lock should be a spinlock */
 
-	if (!list_empty(&tm6000_extension_devlist)) {
-		list_for_each_entry(ops, &tm6000_extension_devlist, next) {
-			if (ops->fillbuf && ops->type == type)
-				ops->fillbuf(dev, buf, size);
-		}
+	list_for_each_entry(ops, &tm6000_extension_devlist, next) {
+		if (ops->fillbuf && ops->type == type)
+			ops->fillbuf(dev, buf, size);
 	}
 
 	return 0;
@@ -898,11 +896,9 @@ void tm6000_init_extension(struct tm6000_core *dev)
 	struct tm6000_ops *ops = NULL;
 
 	mutex_lock(&tm6000_devlist_mutex);
-	if (!list_empty(&tm6000_extension_devlist)) {
-		list_for_each_entry(ops, &tm6000_extension_devlist, next) {
-			if (ops->init)
-				ops->init(dev);
-		}
+	list_for_each_entry(ops, &tm6000_extension_devlist, next) {
+		if (ops->init)
+			ops->init(dev);
 	}
 	mutex_unlock(&tm6000_devlist_mutex);
 }
@@ -912,11 +908,9 @@ void tm6000_close_extension(struct tm6000_core *dev)
 	struct tm6000_ops *ops = NULL;
 
 	mutex_lock(&tm6000_devlist_mutex);
-	if (!list_empty(&tm6000_extension_devlist)) {
-		list_for_each_entry(ops, &tm6000_extension_devlist, next) {
-			if (ops->fini)
-				ops->fini(dev);
-		}
+	list_for_each_entry(ops, &tm6000_extension_devlist, next) {
+		if (ops->fini)
+			ops->fini(dev);
 	}
 	mutex_unlock(&tm6000_devlist_mutex);
 }

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