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

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Date:	Tue, 2 Jul 2013 06:45:27 +0900
From:	Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
To:	akpm@...ux-foundation.org, cl@...ux.com
Cc:	glommer@...allels.com, penberg@...nel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [linux-next-20130422] Bug in SLAB?

Andrew Morton wrote:
> 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!

The patch that fixes above things (commit 6286ae97) went to 3.10.



> 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.
> 
The patch that fixes oops and panic on early boot on architectures with
PAGE_SHIFT + MAX_ORDER > 26 missed 3.10.

> 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.
> 

Somebody needs this patch when debugging with CONFIG_LOCKDEP=y on
architectures with PAGE_SHIFT + MAX_ORDER > 26 .

> Can we get some clarity here please?
> 

Thank you for adding to -mm. But please delete

  Tetsuo said:
  
  : It hangs (with CPU#0 spinning) immediately after printing
  : 
  :   Decompressing Linux... Parsing ELF... done.
  :   Booting the kernel.
  : 
  : lines.

lines from "+ slab-fix-init_lock_keys.patch added to -mm tree", for
these lines are fixed by commit 8a965b3b. Though the same symptom would
appear if hitting this PAGE_SHIFT + MAX_ORDER > 26 bug, I can't confirm
the symptom for environments which I don't have.
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