On 15/11/2018 10:19, Satheesh Rajendran wrote: > On Wed, Nov 14, 2018 at 06:03:19PM +0100, Laurent Vivier wrote: >> Trying to hotplug a CPU on an empty NUMA node (without >> memory or CPU) crashes the kernel when the CPU is onlined. >> >> During the onlining process, the kernel calls start_secondary() >> that ends by calling >> set_numa_mem(local_memory_node(numa_cpu_lookup_table[cpu])) >> that relies on NODE_DATA(nid)->node_zonelists and in our case >> NODE_DATA(nid) is NULL. >> >> To fix that, add the same checking as we already have in >> find_and_online_cpu_nid(): if NODE_DATA() is NULL, use >> the first online node. >> >> Bug: https://github.com/linuxppc/linux/issues/184 >> Fixes: ea05ba7c559c8e5a5946c3a94a2a266e9a6680a6 >> (powerpc/numa: Ensure nodes initialized for hotplug) >> Signed-off-by: Laurent Vivier <lviv...@redhat.com> >> --- >> arch/powerpc/mm/numa.c | 9 +++++++++ >> 1 file changed, 9 insertions(+) > > This patch causes regression for cold plug numa case(Case 1) and > hotplug case + reboot(Case 2) with adding all vcpus into node 0. > > > Env: HW: Power8 Host. > Kernel: 4.20-rc2 + this patch > > Case 1: > 1. boot a guest with 8 vcpus(all available), spreadout in 4 numa nodes. > <vcpu placement='static'>8</vcpu> > ... > <numa> > <cell id='0' cpus='0-1' memory='4194304' unit='KiB'/> > <cell id='1' cpus='2-3' memory='4194304' unit='KiB'/> > <cell id='2' cpus='4-5' memory='0' unit='KiB'/> > <cell id='3' cpus='6-7' memory='0' unit='KiB'/> > </numa> > > 2. Check lscpu --- all vcpus are added to node0 --> NOK > > # lscpu ... > NUMA node0 CPU(s): 0-7 > NUMA node1 CPU(s): > NUMA node2 CPU(s): > NUMA node3 CPU(s): > > without this patch it was working fine. > # lscpu ... > NUMA node0 CPU(s): 0,1 > NUMA node1 CPU(s): 2,3 > NUMA node2 CPU(s): 4,5 > NUMA node3 CPU(s): 6,7 >
Good point. Thank you. I'm going to see what happens and how the cold case allows to online CPUs on nodes with NODE_DATA() set to NULL (because it's what the patch changes). Thanks, Laurent