[1/5] ISDN-Gigaset: Use kmalloc_array() in two functions

From: Markus Elfring <elfring@users.sourceforge.net>
Date: Sun, 25 Sep 2016 22:22:04 +0200

* Multiplications for the size determination of memory allocations
  indicated that array data structures should be processed.
  Thus use the corresponding function "kmalloc_array".

  This issue was detected by using the Coccinelle software.

* Replace the specification of a data structure by a pointer dereference
  to make the corresponding size determination a bit safer according to
  the Linux coding style convention.

Signed-off-by: Markus Elfring <elfring@users.sourceforge.net>
---
 drivers/isdn/gigaset/common.c | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

On Mon, 2016-09-26 at 17:38 +0200, SF Markus Elfring wrote:
> * Multiplications for the size determination of memory allocations
>   indicated that array data structures should be processed.
>   Thus use the corresponding function "kmalloc_array".

Was the current code incorrect? What makes kmalloc_array() better? None
of this is obvious to me.

I'm not going to change code just because some checker suggests to do
so.

>   This issue was detected by using the Coccinelle software.

So? And which coccinelle script was actually used? I couldn't spot a
coccinelle script doing that in the current tree.

> * Replace the specification of a data structure by a pointer dereference
>   to make the corresponding size determination a bit safer according to
>   the Linux coding style convention.

I'm not happy with you mixing this with the above, less trivial,
change.

> Signed-off-by: Markus Elfring <elfring@users.sourceforge.net>

> --- a/drivers/isdn/gigaset/common.c
> +++ b/drivers/isdn/gigaset/common.c
> @@ -709,8 +709,7 @@ struct cardstate *gigaset_initcs(struct gigaset_driver *drv, int channels,
>  
>  	cs->mode = M_UNKNOWN;
>  	cs->mstate = MS_UNINITIALIZED;
> -

Unrelated whitespace change.

> -	cs->bcs = kmalloc(channels * sizeof(struct bc_state), GFP_KERNEL);
> +	cs->bcs = kmalloc_array(channels, sizeof(*cs->bcs), GFP_KERNEL);

For the record: "channels" is basically hardcoded in the three gigaset
hardware drivers.

>  	cs->inbuf = kmalloc(sizeof(struct inbuf_t), GFP_KERNEL);
>  	if (!cs->bcs || !cs->inbuf) {
>  		pr_err("out of memory\n");
> @@ -1089,8 +1088,7 @@ struct gigaset_driver
> *gigaset_initdriver(unsigned minor, unsigned minors,
>  	drv->ops = ops;
>  	drv->owner = owner;
>  	INIT_LIST_HEAD(&drv->list);
> -

Again unrelated whitespace change.

> -	drv->cs = kmalloc(minors * sizeof *drv->cs, GFP_KERNEL);
> +	drv->cs = kmalloc_array(minors, sizeof(*drv->cs), GFP_KERNEL);

For "minors" the same holds as for "channels", above.

And you snuck in a parentheses change. That should have probably been
merged with 5/5.

>  	if (!drv->cs)
>  		goto error;


Paul Bolle

>> * Multiplications for the size determination of memory allocations
>>   indicated that array data structures should be processed.
>>   Thus use the corresponding function "kmalloc_array".
> 
> Was the current code incorrect?

I suggest to use a safer interface for array allocations.


> What makes kmalloc_array() better?

1. How do you think about the safety checks that this function provides?

2. Will you be also affected by further software evolution here?
   2016-07-26
   mm: faster kmalloc_array(), kcalloc()
   https://git.kernel.org/cgit/linux/kernel/git/next/linux-next.git/commit/?id=91c6a05f72a996bee5133e76374ab3ad7d3b9b72


> I'm not going to change code just because some checker suggests to do so.

The script "checkpatch.pl" can point information out like the following.

WARNING: Prefer kmalloc_array over kmalloc with multiply


>>   This issue was detected by using the Coccinelle software.
> 
> So? And which coccinelle script was actually used?

How do you think about to look into related information sources?
https://github.com/coccinelle/coccinelle/issues/81

Would you like to experiment any further with an excerpt?


@replacement1@
expression count, target;
type T;
@@
 target =
-         kmalloc(sizeof(T) * (count)
+         kmalloc_array(count, sizeof(T)
                        , ...);

@replacement2@
expression count, pointer, target;
@@
 target =
-         kmalloc(sizeof(*pointer) * (count)
+         kmalloc_array(count, sizeof(*pointer)
                        , ...);


> I couldn't spot a coccinelle script doing that in the current tree.

This is true for such a software update opportunity.


>> * Replace the specification of a data structure by a pointer dereference
>>   to make the corresponding size determination a bit safer according to
>>   the Linux coding style convention.
> 
> I'm not happy with you mixing this with the above, less trivial, change.

I find that it is a useful combination. - A parameter is adjusted together
with a special function name.


>> -	drv->cs = kmalloc(minors * sizeof *drv->cs, GFP_KERNEL);
>> +	drv->cs = kmalloc_array(minors, sizeof(*drv->cs), GFP_KERNEL);
> 
> For "minors" the same holds as for "channels", above.
> 
> And you snuck in a parentheses change. That should have probably been
> merged with 5/5.

Would you prefer to add them in another update step?

Regards,
Markus

On Wed, 2016-09-28 at 18:38 +0200, SF Markus Elfring wrote:
> > I'm not going to change code just because some checker suggests to
> > do so.
> 
> The script "checkpatch.pl" can point information out like the
> following.
> 
> WARNING: Prefer kmalloc_array over kmalloc with multiply

Am I being trolled?


Paul Bolle