Subject: Re: [PATCH v2] slab: Fix nodeid bounds check for non-contiguous node IDs

From: Yasuaki Ishimatsu <[email-masked]>
Date: Mon, 1 Dec 2014 13:58:08 +0900

(2014/12/01 13:28), Paul Mackerras wrote:
> The bounds check for nodeid in ____cache_alloc_node gives false
> positives on machines where the node IDs are not contiguous, leading
> to a panic at boot time.  For example, on a POWER8 machine the node
> IDs are typically 0, 1, 16 and 17.  This means that num_online_nodes()
> returns 4, so when ____cache_alloc_node is called with nodeid = 16 the
> VM_BUG_ON triggers, like this:
>
> kernel BUG at /home/paulus/kernel/kvm/mm/slab.c:3079!
> Oops: Exception in kernel mode, sig: 5 [#1]
> SMP NR_CPUS=1024 NUMA PowerNV
> Modules linked in:
> CPU: 0 PID: 0 Comm: swapper Not tainted 3.18.0-rc5-kvm+ #17
> task: c0000000013ba230 ti: c000000001494000 task.ti: c000000001494000
> NIP: c000000000264f6c LR: c000000000264f5c CTR: 0000000000000000
> REGS: c0000000014979a0 TRAP: 0700   Not tainted  (3.18.0-rc5-kvm+)
> MSR: 9000000002021032 <SF,HV,VEC,ME,IR,DR,RI>  CR: 28000448  XER: 20000000
> CFAR: c00000000047e978 SOFTE: 0
> GPR00: c000000000264f5c c000000001497c20 c000000001499d48 0000000000000004
> GPR04: 0000000000000100 0000000000000010 0000000000000068 ffffffffffffffff
> GPR08: 0000000000000000 0000000000000001 00000000082d0000 c000000000cca5a8
> GPR12: 0000000048000448 c00000000fda0000 000001003bd44ff0 0000000010020578
> GPR16: 000001003bd44ff8 000001003bd45000 0000000000000001 0000000000000000
> GPR20: 0000000000000000 0000000000000000 0000000000000000 0000000000000010
> GPR24: c000000ffe000080 c000000000c824ec 0000000000000068 c000000ffe000080
> GPR28: 0000000000000010 c000000ffe000080 0000000000000010 0000000000000000
> NIP [c000000000264f6c] .____cache_alloc_node+0x6c/0x270
> LR [c000000000264f5c] .____cache_alloc_node+0x5c/0x270
> Call Trace:
> [c000000001497c20] [c000000000264f5c] .____cache_alloc_node+0x5c/0x270 (unreliable)
> [c000000001497cf0] [c00000000026552c] .kmem_cache_alloc_node_trace+0xdc/0x360
> [c000000001497dc0] [c000000000c824ec] .init_list+0x3c/0x128
> [c000000001497e50] [c000000000c827b4] .kmem_cache_init+0x1dc/0x258
> [c000000001497ef0] [c000000000c54090] .start_kernel+0x2a0/0x568
> [c000000001497f90] [c000000000008c6c] start_here_common+0x20/0xa8
> Instruction dump:
> 7c7d1b78 7c962378 4bda4e91 60000000 3c620004 38800100 386370d8 48219959
> 60000000 7f83e000 7d301026 5529effe <0b090000> 393c0010 79291f24 7d3d4a14
>
> To fix this, we instead compare the nodeid with MAX_NUMNODES, and
> additionally make sure it isn't negative (since nodeid is an int).
> The check is there mainly to protect the array dereference in the
> get_node() call in the next line, and the array being dereferenced is
> of size MAX_NUMNODES.  If the nodeid is in range but invalid (for
> example if the node is off-line), the BUG_ON in the next line will
> catch that.
>
> Signed-off-by: Paul Mackerras <[email-masked]>
> ---

Looks good to me.

Reviewed-by: Yasuaki Ishimatsu <[email-masked]>

If you need to backport it into -stable kernel, please read
Documentation/stable_kernel_rules.txt.

Thanks,
Yasuaki Ishimatsu

> v2: include the oops message in the patch description
>
>   mm/slab.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/mm/slab.c b/mm/slab.c
> index eb2b2ea..f34e053 100644
> --- a/mm/slab.c
> +++ b/mm/slab.c
> @@ -3076,7 +3076,7 @@ static void *____cache_alloc_node(struct kmem_cache *cachep, gfp_t flags,
>   	void *obj;
>   	int x;
>
> -	VM_BUG_ON(nodeid > num_online_nodes());
> +	VM_BUG_ON(nodeid < 0 || nodeid >= MAX_NUMNODES);
>   	n = get_node(cachep, nodeid);
>   	BUG_ON(!n);
>
>