linux-kernel - Re: [RFC][PATCH 0/5] do not dereference NULL pools in pools' destroy() functions

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Date:	Tue, 09 Jun 2015 17:06:09 -0700
From:	Joe Perches <joe@...ches.com>
To:	Andrew Morton <akpm@...ux-foundation.org>,
	Julia Lawall <julia.lawall@...6.fr>
Cc:	Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
	Minchan Kim <minchan@...nel.org>,
	Christoph Lameter <cl@...ux.com>,
	Pekka Enberg <penberg@...nel.org>,
	Joonsoo Kim <iamjoonsoo.kim@....com>,
	Michal Hocko <mhocko@...e.cz>,
	David Rientjes <rientjes@...gle.com>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, sergey.senozhatsky.work@...il.com
Subject: Re: [RFC][PATCH 0/5] do not dereference NULL pools in pools'
 destroy() functions

On Tue, 2015-06-09 at 14:25 -0700, Andrew Morton wrote:
> On Tue,  9 Jun 2015 21:04:48 +0900 Sergey Senozhatsky <sergey.senozhatsky@...il.com> wrote:
> 
> > The existing pools' destroy() functions do not allow NULL pool pointers;
> > instead, every destructor() caller forced to check if pool is not NULL,
> > which:
> >  a) requires additional attention from developers/reviewers
> >  b) may lead to a NULL pointer dereferences if (a) didn't work
> > 
> > 
> > First 3 patches tweak
> > - kmem_cache_destroy()
> > - mempool_destroy()
> > - dma_pool_destroy()
> > 
> > to handle NULL pointers.
> 
> Well I like it, even though it's going to cause a zillion little cleanup
> patches.
> 
> checkpatch already has a "kfree(NULL) is safe and this check is
> probably not required" test so I guess Joe will need to get busy ;)

Maybe it'll be Julia's crew.

The checkpatch change is pretty trivial
---
 scripts/checkpatch.pl | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/scripts/checkpatch.pl b/scripts/checkpatch.pl
index 69c4716..3d6e34d 100755
--- a/scripts/checkpatch.pl
+++ b/scripts/checkpatch.pl
@@ -4801,7 +4801,7 @@ sub process {
 # check for needless "if (<foo>) fn(<foo>)" uses
 		if ($prevline =~ /\bif\s*\(\s*($Lval)\s*\)/) {
 			my $expr = '\s*\(\s*' . quotemeta($1) . '\s*\)\s*;';
-			if ($line =~ /\b(kfree|usb_free_urb|debugfs_remove(?:_recursive)?)$expr/) {
+			if ($line =~ /\b(kfree|usb_free_urb|debugfs_remove(?:_recursive)?|(?:kmem_cache|mempool|dma_pool)_destroy)$expr/) {
 				WARN('NEEDLESS_IF',
 				     "$1(NULL) is safe and this check is probably not required\n" . $hereprev);
 			}


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