Re: no need to check for NULL before calling kfree() -fs/ext2/

[Jesper Juhl]

On Wed, 30 Mar 2005, P Lavin wrote:

> Date: Wed, 30 Mar 2005 12:45:01 +0530
> From: P Lavin <lavin.p@xxxxxxxxxxxxxxxxxx>
> To: linux-kernel@xxxxxxxxxxxxxxx
> Subject: Re: no need to check for NULL before calling kfree() -fs/ext2/
> 
> Hi,
> In my wlan driver module, i allocated some memory using kmalloc in interrupt
> context, this one failed but its not returning NULL , 

kmalloc() should always return NULL if the allocation failed.


>so i was proceeding
> further everything was going wrong... & finally the kernel crahed. Can any one
> of you tell me why this is happening ? i cannot use GFP_KERNEL because i'm
> calling this function from interrupt context & it may block. Any other

If you need to allocate memory from interrupt context you should be using 
GFP_ATOMIC (or, if possible, do the allocation earlier in a different 
context).


> solution for this ?? I'm concerned abt why kmalloc is not returning null if
> its not a success ??
> 
I have no explanation for that, are you sure that's really what's 
happening?


> Is it not necessary to check for NULL before calling kfree() ??

No, it is not nessesary to check for NULL before calling kfree() since 
kfree() does    

void kfree (const void *objp)
{
	... 
        if (!objp)
                return;
	...
}

So, if you pass kfree() a NULL pointer it deals with it itself, you don't 
need to check that explicitly before calling kfree() - that's redundant.


-- 
Jesper Juhl


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