[PATCH 2.6.19] drivers/media/video/cpia2/cpia2_usb.c: Free previously allocated memory (in array elements) if kmalloc() returns NULL.

[PATCH 2.6.19] drivers/media/video/cpia2/cpia2_usb.c: Free previously allocated memory (in array elements) if kmalloc() returns NULL.

[Amit Choudhary]

Description: Free previously allocated memory (in array elements) if kmalloc() returns NULL, in function submit_urbs(), in file drivers/media/video/cpia2/cpia2_usb.c. If the system is low on memory, then previously allocated memory in the same array should be freed up to help the system recover.

Signed-off-by: Amit Choudhary <amit2030@gmail.com>

diff --git a/drivers/media/video/cpia2/cpia2_usb.c b/drivers/media/video/cpia2/cpia2_usb.c
index 28dc6a1..c938638 100644
--- a/drivers/media/video/cpia2/cpia2_usb.c
+++ b/drivers/media/video/cpia2/cpia2_usb.c
@@ -640,6 +640,10 @@ static int submit_urbs(struct camera_dat
 		cam->sbuf[i].data =
 		    kmalloc(FRAMES_PER_DESC * FRAME_SIZE_PER_DESC, GFP_KERNEL);
 		if (!cam->sbuf[i].data) {
+			for (--i; i >= 0; i--) {
+				kfree(cam->sbuf[i].data);
+				cam->sbuf[i].data = NULL;
+			}
 			return -ENOMEM;
 		}
 	}

Re: [PATCH 2.6.19] drivers/media/video/cpia2/cpia2_usb.c: Free previously allocated memory (in array elements) if kmalloc() returns NULL.

[Mariusz Kozlowski]

Hello,

> --- a/drivers/media/video/cpia2/cpia2_usb.c
> +++ b/drivers/media/video/cpia2/cpia2_usb.c
> @@ -640,6 +640,10 @@ static int submit_urbs(struct camera_dat
>  		cam->sbuf[i].data =
>  		    kmalloc(FRAMES_PER_DESC * FRAME_SIZE_PER_DESC, GFP_KERNEL);
>  		if (!cam->sbuf[i].data) {
> +			for (--i; i >= 0; i--) {
> +				kfree(cam->sbuf[i].data);
> +				cam->sbuf[i].data = NULL;
> +			}
>  			return -ENOMEM;
>  		}
>  	}

Just for future. Shorter and more readable version of your for(...) thing:

	while (i--) {
		...
	}

-- 
Regards,

	Mariusz Kozlowski

Re: [PATCH 2.6.19] drivers/media/video/cpia2/cpia2_usb.c: Free previously allocated memory (in array elements) if kmalloc() returns NULL.

[David Rientjes]

On Fri, 8 Dec 2006, Mariusz Kozlowski wrote:

> > --- a/drivers/media/video/cpia2/cpia2_usb.c
> > +++ b/drivers/media/video/cpia2/cpia2_usb.c
> > @@ -640,6 +640,10 @@ static int submit_urbs(struct camera_dat
> >  		cam->sbuf[i].data =
> >  		    kmalloc(FRAMES_PER_DESC * FRAME_SIZE_PER_DESC, GFP_KERNEL);
> >  		if (!cam->sbuf[i].data) {
> > +			for (--i; i >= 0; i--) {
> > +				kfree(cam->sbuf[i].data);
> > +				cam->sbuf[i].data = NULL;
> > +			}
> >  			return -ENOMEM;
> >  		}
> >  	}
> 
> Just for future. Shorter and more readable version of your for(...) thing:
> 
> 	while (i--) {
> 		...
> 	}
> 

No, that is not equivalent.

You want
	while (i-- >= 0) {
		...
	}

Re: [PATCH 2.6.19] drivers/media/video/cpia2/cpia2_usb.c: Free previously allocated memory (in array elements) if kmalloc() returns NULL.

[Mariusz Kozlowski]

Hello, 

> > Just for future. Shorter and more readable version of your for(...) thing:
> > 
> > 	while (i--) {
> > 		...
> > 	}
> > 
> 
> No, that is not equivalent.
> 
> You want
> 	while (i-- >= 0) {
> 		...
> 	}
> 

Not really. That will stop at -1 not 0.

-- 
Regards,

	Mariusz Kozlowski

Re: [PATCH 2.6.19] drivers/media/video/cpia2/cpia2_usb.c: Free previously allocated memory (in array elements) if kmalloc() returns NULL.

[David Rientjes]

On Fri, 8 Dec 2006, Mariusz Kozlowski wrote:

> > > Just for future. Shorter and more readable version of your for(...) thing:
> > > 
> > > 	while (i--) {
> > > 		...
> > > 	}
> > > 
> > 
> > No, that is not equivalent.
> > 
> > You want
> > 	while (i-- >= 0) {
> > 		...
> > 	}
> > 
> 
> Not really. That will stop at -1 not 0.
> 

It depends on your intent.  Generally speaking,

	while (i--) {
		...
	}

is never what you want.  Adding the check for being greater than 0 stops 
potential bugs from signed int i being negative.  The only drawback on x86 
is that it sets a byte based on the greater condition with setg and tests 
it later with testb for every iteration.  This use of testb will _always_ 
use the same addressable byte registers for both its operands.

Based on this particular patch, I agree that

	while (i-- > 0) {
		...
	}

will do the job.  This is equivalent to the original for loop and ensures 
that a negative value of i is never iterated on (even though it admittedly 
would never be negative in this instance to begin with).

		David