Re: "slab: Fix missing DEBUG_SLAB last user" breaks ARM

[Russell King <rmk@arm.linux.org.uk>]

On Tue, Feb 08, 2011 at 07:44:56AM +0200, Pekka Enberg wrote:
> Hi!
> 
> On Mon, Feb 7, 2011 at 8:06 PM, Russell King <rmk@arm.linux.org.uk> wrote:
> > commit 5c5e3b33 appears to break ARM thusly:
> >
> > | Mount-cache hash table entries: 512
> > | slab error in verify_redzone_free(): cache `idr_layer_cache': memory outside object was overwritten
> > | Backtrace:
> > | [<c0227088>] (dump_backtrace+0x0/0x110) from [<c0431afc>] (dump_stack+0x18/0x1c)
> > | [<c0431ae4>] (dump_stack+0x0/0x1c) from [<c0293304>] (__slab_error+0x28/0x30)
> > | [<c02932dc>] (__slab_error+0x0/0x30) from [<c0293a74>] (cache_free_debugcheck+0x1c0/0x2b8)
> > | [<c02938b4>] (cache_free_debugcheck+0x0/0x2b8) from [<c0293f78>] (kmem_cache_free+0x3c/0xc0)
> > | [<c0293f3c>] (kmem_cache_free+0x0/0xc0) from [<c032b1c8>] (ida_get_new_above+0x19c/0x1c0)
> > | [<c032b02c>] (ida_get_new_above+0x0/0x1c0) from [<c02af7ec>] (alloc_vfsmnt+0x54/0x144)
> > | [<c02af798>] (alloc_vfsmnt+0x0/0x144) from [<c0299830>] (vfs_kern_mount+0x30/0xec)
> > | [<c0299800>] (vfs_kern_mount+0x0/0xec) from [<c0299908>] (kern_mount_data+0x1c/0x20)
> > | [<c02998ec>] (kern_mount_data+0x0/0x20) from [<c02146c4>] (sysfs_init+0x68/0xc8)
> > | [<c021465c>] (sysfs_init+0x0/0xc8) from [<c02137d4>] (mnt_init+0x90/0x1b0)
> > | [<c0213744>] (mnt_init+0x0/0x1b0) from [<c0213388>] (vfs_caches_init+0x100/0x140)
> > | [<c0213288>] (vfs_caches_init+0x0/0x140) from [<c0208c0c>] (start_kernel+0x2e8/0x368)
> > | [<c0208924>] (start_kernel+0x0/0x368) from [<c0208034>] (__enable_mmu+0x0/0x2c)
> > | c0113268: redzone 1:0xd84156c5c032b3ac, redzone 2:0xd84156c5635688c0.
> > | slab error in cache_alloc_debugcheck_after(): cache `idr_layer_cache': double free, or memory outside object was overwritten
> > | ...
> > | c011307c: redzone 1:0x9f91102ffffffff, redzone 2:0x9f911029d74e35b
> > | slab: Internal list corruption detected in cache 'idr_layer_cache'(24), slabp c0113000(16). Hexdump:
> > |
> > | 000: 20 4f 10 c0 20 4f 10 c0 7c 00 00 00 7c 30 11 c0
> > | 010: 10 00 00 00 10 00 00 00 00 00 c9 17 fe ff ff ff
> > | 020: fe ff ff ff fe ff ff ff fe ff ff ff fe ff ff ff
> > | 030: fe ff ff ff fe ff ff ff fe ff ff ff fe ff ff ff
> > | 040: fe ff ff ff fe ff ff ff fe ff ff ff fe ff ff ff
> > | 050: fe ff ff ff fe ff ff ff fe ff ff ff 11 00 00 00
> > | 060: 12 00 00 00 13 00 00 00 14 00 00 00 15 00 00 00
> > | 070: 16 00 00 00 17 00 00 00 c0 88 56 63
> > | kernel BUG at /home/rmk/git/linux-2.6-rmk/mm/slab.c:2928!
> >
> > This hasn't been noticed as I guess not many people use SLAB on ARM
> > anymore, and even less people probably have SLAB debugging enabled.
> > With SLAB debugging disabled, the system appears to behave correctly -
> > or maybe the problem is just hidden.
> 
> I thought the fix was for ARM, actually, but unfortunately the
> changelog is somewhat terse (shame on me). Hmm?

As you say, the changelog is soo terse that we now have no idea why this
commit was created.

So, what's the fix here?  It looks to me like a revert is in order.

I suggest that if it does get reverted, a copy of my original bug report
is included in the revert commit so that all the details are available if
it needs revisiting.

-- 
Russell King
 Linux kernel    2.6 ARM Linux   - http://www.arm.linux.org.uk/
 maintainer of: