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

[Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>]

Andrew Morton wrote:
> Look, I'll make this easier:
> 
> : Subject: slab: fix init_lock_keys
> : 
> : In 3.10 kernels with CONFIG_LOCKDEP=y on architectures with
> : PAGE_SHIFT + MAX_ORDER > 26 such as [architecture goes here], the kernel does
> : [x] when the user does [y].
> :
> : init_lock_keys() goes too far in initializing values in kmalloc_caches
> : because it assumed that the size of the kmalloc array goes up to
> : MAX_ORDER.  However, the size of the kmalloc array for SLAB may be
> : restricted due to increased page sizes or CONFIG_FORCE_MAX_ZONEORDER.
> :
> : Fix this by [z].
> 
> 
> Please fill in the text within [].
> 
OK. I made from http://marc.info/?l=linux-kernel&m=136810234704350&w=2 .
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Some architectures (e.g. powerpc built with CONFIG_PPC_256K_PAGES=y
CONFIG_FORCE_MAX_ZONEORDER=11) get PAGE_SHIFT + MAX_ORDER > 26.

In 3.10 kernels, CONFIG_LOCKDEP=y with PAGE_SHIFT + MAX_ORDER > 26 makes
init_lock_keys() dereference beyond kmalloc_caches[26].
This leads to an unbootable system (kernel panic at initializing SLAB)
if one of kmalloc_caches[26...PAGE_SHIFT+MAX_ORDER-1] is not NULL.

Fix this by making sure that init_lock_keys() does not dereference beyond
kmalloc_caches[26] arrays.
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