linux-kernel - Re: [PATCH] mm/sl[aou]b: make kfree() aware of error pointers

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Date:	Tue, 9 Sep 2014 16:21:14 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Jiri Kosina <jkosina@...e.cz>
Cc:	Christoph Lameter <cl@...ux.com>,
	Pekka Enberg <penberg@...nel.org>,
	David Rientjes <rientjes@...gle.com>,
	Joonsoo Kim <iamjoonsoo.kim@....com>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	Dan Carpenter <dan.carpenter@...cle.com>,
	"Theodore Ts'o" <tytso@....edu>
Subject: Re: [PATCH] mm/sl[aou]b: make kfree() aware of error pointers

On Tue, 9 Sep 2014 23:25:28 +0200 (CEST) Jiri Kosina <jkosina@...e.cz> wrote:

> kfree() is happy to accept NULL pointer and does nothing in such case. 
> It's reasonable to expect it to behave the same if ERR_PTR is passed to 
> it.
> 
> Inspired by a9cfcd63e8d ("ext4: avoid trying to kfree an ERR_PTR 
> pointer").
> 
> ...
>
> --- a/mm/slab.c
> +++ b/mm/slab.c
> @@ -3612,7 +3612,7 @@ void kfree(const void *objp)
>  
>  	trace_kfree(_RET_IP_, objp);
>  
> -	if (unlikely(ZERO_OR_NULL_PTR(objp)))
> +	if (unlikely(ZERO_OR_NULL_PTR(objp) || IS_ERR(objp)))
>  		return;

kfree() is quite a hot path to which this will add overhead.  And we
have (as far as we know) no code which will actually use this at
present.

How about a new

kfree_safe(...)
{
	if (IS_ERR(...))
		return;
	if (other-stuff-when-we-think-of-it)
		return;
	kfree(...);
}

?
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