On 21.05.2014 [14:58:12 -0400], Tejun Heo wrote: > Hello, > > On Wed, May 21, 2014 at 09:16:27AM -0500, Christoph Lameter wrote: > > On Mon, 19 May 2014, Nishanth Aravamudan wrote: > > > I'm seeing a panic at boot with this change on an LPAR which actually > > > has no Node 0. Here's what I think is happening: > > > > > > start_kernel > > > ... > > > -> setup_per_cpu_areas > > > -> pcpu_embed_first_chunk > > > -> pcpu_fc_alloc > > > -> ___alloc_bootmem_node(NODE_DATA(cpu_to_node(cpu), ... > > > -> smp_prepare_boot_cpu > > > -> set_numa_node(boot_cpuid) > > > > > > So we panic on the NODE_DATA call. It seems that ia64, at least, uses > > > pcpu_alloc_first_chunk rather than embed. x86 has some code to handle > > > early calls of cpu_to_node (early_cpu_to_node) and sets the mapping for > > > all CPUs in setup_per_cpu_areas(). > > > > Maybe we can switch ia64 too embed? Tejun: Why are there these > > dependencies? > > > > > Thoughts? Does that mean we need something similar to x86 for powerpc? > > I'm missing context to properly understand what's going on but the > specific allocator in use shouldn't matter. e.g. x86 can use both > embed and page allocators. If the problem is that the arch is > accessing percpu memory before percpu allocator is initialized and the > problem was masked before somehow, the right thing to do would be > removing those premature percpu accesses. If early percpu variables > are really necessary, doing similar early_percpu thing as in x86 would > be necessary. The early access is in the arch's pcpu_alloc_bootmem. On x86, rather than using NODE_DATA(cpu_to_node), it uses (in pcpu_alloc_bootmem), early_cpu_to_node(cpu) with their custom logic. The issue is that cpu_to_node, if USE_PERCPU_NUMA_NODE_ID is defined (which it is for NUMA powerpc, x86, ia64), is that cpu_to_node uses the percpu area, which data isn't initialized yet. So I guess powerpc needs the same treatment as x86. Thanks, Nish -- 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>