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 <paulus@xxxxxxxxx> --- 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); -- 2.1.1 -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>