linux-kernel - Re: [linux-next-20130422] Bug in SLAB?

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Message-Id: <20130701130903.61459f57f4ba31e282065001@linux-foundation.org>
Date:	Mon, 1 Jul 2013 13:09:03 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Christoph Lameter <cl@...ux.com>
Cc:	Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>,
	glommer@...allels.com, penberg@...nel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [linux-next-20130422] Bug in SLAB?

On Tue, 7 May 2013 14:28:49 +0000 Christoph Lameter <cl@...ux.com> wrote:

> On Tue, 7 May 2013, Tetsuo Handa wrote:
> 
> > > These are exclusively from the module load. So the kernel seems to be
> > > clean of large kmalloc's ?
> > >
> > There are modules (e.g. TOMOYO) which do not check for KMALLOC_MAX_SIZE limit
> > and expect kmalloc() larger than KMALLOC_MAX_SIZE bytes to return NULL.
> 
> Dont do that. Please fix these things.

Slab should return NULL for a request greater than KMALLOC_MAX_SIZE. 
For heaven's sake don't break that!

What's going on with this bug, btw?  This:

--- a/mm/slab.c~slab-fix-init_lock_keys
+++ a/mm/slab.c
@@ -565,7 +565,7 @@ static void init_node_lock_keys(int q)
 	if (slab_state < UP)
 		return;
 
-	for (i = 1; i < PAGE_SHIFT + MAX_ORDER; i++) {
+	for (i = 1; i <= KMALLOC_SHIFT_HIGH; i++) {
 		struct kmem_cache_node *n;
 		struct kmem_cache *cache = kmalloc_caches[i];
 

still seems to be unapplied.

I've read through the thread trying to work out what the end-user
impact of that fix is, but it's all clear as mud.  It's possible that
the end-user effect is `kernel locks up after printing "Booting the
kernel"'.  Or maybe not.

And if the above patch does indeed fix something significant, we might
need a -stable backport.

Can we get some clarity here please?
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