Messages in this thread | | | Date | Thu, 15 Nov 2018 14:49:48 +0530 | From | Satheesh Rajendran <> | Subject | Re: [PATCH] powerpc/numa: fix hot-added CPU on memory-less node |
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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 <lvivier@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 Architecture: ppc64le Byte Order: Little Endian CPU(s): 8 On-line CPU(s) list: 0-7 Thread(s) per core: 1 Core(s) per socket: 8 Socket(s): 1 NUMA node(s): 4 Model: 2.1 (pvr 004b 0201) Model name: POWER8 (architected), altivec supported Hypervisor vendor: KVM Virtualization type: para L1d cache: 64K L1i cache: 32K 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 Architecture: ppc64le Byte Order: Little Endian CPU(s): 8 On-line CPU(s) list: 0-7 Thread(s) per core: 1 Core(s) per socket: 8 Socket(s): 1 NUMA node(s): 4 Model: 2.1 (pvr 004b 0201) Model name: POWER8 (architected), altivec supported Hypervisor vendor: KVM Virtualization type: para L1d cache: 64K L1i cache: 32K NUMA node0 CPU(s): 0,1 NUMA node1 CPU(s): 2,3 NUMA node2 CPU(s): 4,5 NUMA node3 CPU(s): 6,7
Case 2: 1. boot a guest with 8 vcpus(2 available, 6 possible), spreadout in 4 numa nodes. <vcpu placement='static' current='2'>8</vcpu> ... <numa> <cell id='0' cpus='0-1' memory='0' 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. Hotplug all vcpus # lscpu Architecture: ppc64le Byte Order: Little Endian CPU(s): 8 On-line CPU(s) list: 0-7 Thread(s) per core: 1 Core(s) per socket: 8 Socket(s): 1 NUMA node(s): 2 Model: 2.1 (pvr 004b 0201) Model name: POWER8 (architected), altivec supported Hypervisor vendor: KVM Virtualization type: para L1d cache: 64K L1i cache: 32K NUMA node0 CPU(s): 0,1,4-7 NUMA node1 CPU(s): 2,3
3. reboot the guest # lscpu Architecture: ppc64le Byte Order: Little Endian CPU(s): 8 On-line CPU(s) list: 0-7 Thread(s) per core: 1 Core(s) per socket: 8 Socket(s): 1 NUMA node(s): 4 Model: 2.1 (pvr 004b 0201) Model name: POWER8 (architected), altivec supported Hypervisor vendor: KVM Virtualization type: para L1d cache: 64K L1i cache: 32K NUMA node0 CPU(s): 0-7 NUMA node1 CPU(s): NUMA node2 CPU(s): NUMA node3 CPU(s):
Without this patch, Case 2 crashes the guest during hotplug, i.e issue reported in https://github.com/linuxppc/linux/issues/184
Regards, -Satheesh.
> > diff --git a/arch/powerpc/mm/numa.c b/arch/powerpc/mm/numa.c > index 3a048e98a132..1b2d25a3c984 100644 > --- a/arch/powerpc/mm/numa.c > +++ b/arch/powerpc/mm/numa.c > @@ -483,6 +483,15 @@ static int numa_setup_cpu(unsigned long lcpu) > if (nid < 0 || !node_possible(nid)) > nid = first_online_node; > > + if (NODE_DATA(nid) == NULL) { > + /* > + * Default to using the nearest node that has memory installed. > + * Otherwise, it would be necessary to patch the kernel MM code > + * to deal with more memoryless-node error conditions. > + */ > + nid = first_online_node; > + } > + > map_cpu_to_node(lcpu, nid); > of_node_put(cpu); > out: > -- > 2.17.2 >
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