[PATCH 1/1] dm: Deletion of unnecessary checks before two function calls

[PATCH 1/1] dm: Deletion of unnecessary checks before two function calls

[SF Markus Elfring]

From: Markus Elfring <elfring@users.sourceforge.net>
Date: Wed, 19 Nov 2014 21:48:10 +0100

The functions dm_table_destroy() and vfree() perform also input
parameter validation. Thus the test around the call is not needed.

This issue was detected by using the Coccinelle software.

Signed-off-by: Markus Elfring <elfring@users.sourceforge.net>
---
 drivers/md/dm-ioctl.c           |  3 +--
 drivers/md/dm-snap-persistent.c | 12 ++++--------
 2 files changed, 5 insertions(+), 10 deletions(-)

diff --git a/drivers/md/dm-ioctl.c b/drivers/md/dm-ioctl.c
index 5152142..0b925a4 100644
--- a/drivers/md/dm-ioctl.c
+++ b/drivers/md/dm-ioctl.c
@@ -1050,8 +1050,7 @@ static int do_resume(struct dm_ioctl *param)
 	 * Since dm_swap_table synchronizes RCU, nobody should be in
 	 * read-side critical section already.
 	 */
-	if (old_map)
-		dm_table_destroy(old_map);
+	dm_table_destroy(old_map);
 
 	if (!r)
 		__dev_status(md, param);
diff --git a/drivers/md/dm-snap-persistent.c b/drivers/md/dm-snap-persistent.c
index d6e8817..4b29bac 100644
--- a/drivers/md/dm-snap-persistent.c
+++ b/drivers/md/dm-snap-persistent.c
@@ -200,16 +200,13 @@ err_area:
 
 static void free_area(struct pstore *ps)
 {
-	if (ps->area)
-		vfree(ps->area);
+	vfree(ps->area);
 	ps->area = NULL;
 
-	if (ps->zero_area)
-		vfree(ps->zero_area);
+	vfree(ps->zero_area);
 	ps->zero_area = NULL;
 
-	if (ps->header_area)
-		vfree(ps->header_area);
+	vfree(ps->header_area);
 	ps->header_area = NULL;
 }
 
@@ -605,8 +602,7 @@ static void persistent_dtr(struct dm_exception_store *store)
 	free_area(ps);
 
 	/* Allocated in persistent_read_metadata */
-	if (ps->callbacks)
-		vfree(ps->callbacks);
+	vfree(ps->callbacks);
 
 	kfree(ps);
 }
-- 
2.1.3

[PATCH 1/3] dm snapshot: Deletion of unnecessary checks before the function call "vfree"

[SF Markus Elfring]

From: Markus Elfring <elfring@users.sourceforge.net>
Date: Mon, 2 Feb 2015 14:38:29 +0100

The vfree() function performs also input parameter validation.
Thus the test around the call is not needed.

This issue was detected by using the Coccinelle software.

Signed-off-by: Markus Elfring <elfring@users.sourceforge.net>
---
 drivers/md/dm-snap-persistent.c | 14 ++++----------
 1 file changed, 4 insertions(+), 10 deletions(-)

diff --git a/drivers/md/dm-snap-persistent.c b/drivers/md/dm-snap-persistent.c
index d6e8817..808b841 100644
--- a/drivers/md/dm-snap-persistent.c
+++ b/drivers/md/dm-snap-persistent.c
@@ -200,16 +200,11 @@ err_area:
 
 static void free_area(struct pstore *ps)
 {
-	if (ps->area)
-		vfree(ps->area);
+	vfree(ps->area);
 	ps->area = NULL;
-
-	if (ps->zero_area)
-		vfree(ps->zero_area);
+	vfree(ps->zero_area);
 	ps->zero_area = NULL;
-
-	if (ps->header_area)
-		vfree(ps->header_area);
+	vfree(ps->header_area);
 	ps->header_area = NULL;
 }
 
@@ -605,8 +600,7 @@ static void persistent_dtr(struct dm_exception_store *store)
 	free_area(ps);
 
 	/* Allocated in persistent_read_metadata */
-	if (ps->callbacks)
-		vfree(ps->callbacks);
+	vfree(ps->callbacks);
 
 	kfree(ps);
 }
-- 
2.2.2

[PATCH 3/3] dm ioctl: Delete an unnecessary check before the function call "dm_table_destroy"

[SF Markus Elfring]

From: Markus Elfring <elfring@users.sourceforge.net>
Date: Mon, 2 Feb 2015 15:30:37 +0100

The dm_table_destroy() function tests whether its argument is NULL and then
returns immediately. Thus the test around the call is not needed.

This issue was detected by using the Coccinelle software.

Signed-off-by: Markus Elfring <elfring@users.sourceforge.net>
---
 drivers/md/dm-ioctl.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/drivers/md/dm-ioctl.c b/drivers/md/dm-ioctl.c
index 73f791b..4fac6cf 100644
--- a/drivers/md/dm-ioctl.c
+++ b/drivers/md/dm-ioctl.c
@@ -1053,8 +1053,7 @@ static int do_resume(struct dm_ioctl *param)
 	 * Since dm_swap_table synchronizes RCU, nobody should be in
 	 * read-side critical section already.
 	 */
-	if (old_map)
-		dm_table_destroy(old_map);
+	dm_table_destroy(old_map);
 
 	if (!r)
 		__dev_status(md, param);
-- 
2.2.2

Re: [PATCH 3/3] dm ioctl: Delete an unnecessary check before the function call "dm_table_destroy"

[Mike Snitzer]

On Mon, Feb 02 2015 at 10:23am -0500,
SF Markus Elfring <elfring@users.sourceforge.net> wrote:

> From: Markus Elfring <elfring@users.sourceforge.net>
> Date: Mon, 2 Feb 2015 15:30:37 +0100
> 
> The dm_table_destroy() function tests whether its argument is NULL and then
> returns immediately. Thus the test around the call is not needed.
> 
> This issue was detected by using the Coccinelle software.

Your proposed patch (while technically correct) hurts code clarity.

Nack.

Re: [PATCH 3/3] dm ioctl: Delete an unnecessary check before the function call "dm_table_destroy"

[SF Markus Elfring]

> Your proposed patch (while technically correct) hurts code clarity.

How many source code readability and understanding challenges does each
additional condition check cause?

Can the affected place become also a bit more efficient?

Regards,
Markus

Re: [PATCH 3/3] dm ioctl: Delete an unnecessary check before the function call "dm_table_destroy"

[Mike Snitzer]

On Sun, Feb 8, 2015 at 4:55 AM, SF Markus Elfring
<elfring@users.sourceforge.net> wrote:
>> Your proposed patch (while technically correct) hurts code clarity.
>
> How many source code readability and understanding challenges does each
> additional condition check cause?

Please don't make a mountain out of a mole hill in an attempt to
defend your robotic patch (I'm quite tired of some of these static
analyzer patch submissions).

FYI, I did stage your other patch for 3.20, see:
https://git.kernel.org/cgit/linux/kernel/git/device-mapper/linux-dm.git/commit/?h=dm-for-3.20&id=d0ce7e911c97c7c6df1081dcedfefced82a0c6bf

> Can the affected place become also a bit more efficient?

Efficiency isn't a concern in this instance (it isn't a hot IO path).
And even if it were, a branch (with current code) is more efficient vs
a a jump + branch (your proposed patch) -- in the case that no active
table exists.  Now if it likely that old_map does exist then yes your
patch is always a very slight win.

But given the duality of the calling function (deals with loading a
new map and destroying the old map if it exists) I prefer to keep the
code as is.  Sorry.

Re: [PATCH 3/3] dm ioctl: Delete an unnecessary check before the function call "dm_table_destroy"

[SF Markus Elfring]

> FYI, I did stage your other patch for 3.20, see:
> https://git.kernel.org/cgit/linux/kernel/git/device-mapper/linux-dm.git/commit/?h=dm-for-3.20&id=d0ce7e911c97c7c6df1081dcedfefced82a0c6bf

Thanks for your acceptance of the suggested clean-up around
vfree() function calls at least.
Additional source code places can also be reconsidered at other times,
can't they?

Regards,
Markus