From: "Mike Rapoport (IBM)" rppt@kernel.org
[ Upstream commit a1e2b8b36820d8c91275f207e77e91645b7c6836 ]
Qi Zheng reported crashes in a production environment and provided a simplified example as a reproducer:
| For example, if we use Qemu to start a two NUMA node kernel, | one of the nodes has 2M memory (less than NODE_MIN_SIZE), | and the other node has 2G, then we will encounter the | following panic: | | BUG: kernel NULL pointer dereference, address: 0000000000000000 | <...> | RIP: 0010:_raw_spin_lock_irqsave+0x22/0x40 | <...> | Call Trace: | <TASK> | deactivate_slab() | bootstrap() | kmem_cache_init() | start_kernel() | secondary_startup_64_no_verify()
The crashes happen because of inconsistency between the nodemask that has nodes with less than 4MB as memoryless, and the actual memory fed into the core mm.
The commit:
9391a3f9c7f1 ("[PATCH] x86_64: Clear more state when ignoring empty node in SRAT parsing")
... that introduced minimal size of a NUMA node does not explain why a node size cannot be less than 4MB and what boot failures this restriction might fix.
Fixes have been submitted to the core MM code to tighten up the memory topologies it accepts and to not crash on weird input:
mm: page_alloc: skip memoryless nodes entirely mm: memory_hotplug: drop memoryless node from fallback lists
Andrew has accepted them into the -mm tree, but there are no stable SHA1's yet.
This patch drops the limitation for minimal node size on x86:
- which works around the crash without the fixes to the core MM. - makes x86 topologies less weird, - removes an arbitrary and undocumented limitation on NUMA topologies.
[ mingo: Improved changelog clarity. ]
Reported-by: Qi Zheng zhengqi.arch@bytedance.com Tested-by: Mario Casquero mcasquer@redhat.com Signed-off-by: Mike Rapoport (IBM) rppt@kernel.org Signed-off-by: Ingo Molnar mingo@kernel.org Acked-by: David Hildenbrand david@redhat.com Acked-by: Michal Hocko mhocko@suse.com Cc: Dave Hansen dave.hansen@linux.intel.com Cc: Rik van Riel riel@surriel.com Link: https://lore.kernel.org/r/ZS+2qqjEO5/867br@gmail.com Signed-off-by: Sasha Levin sashal@kernel.org --- arch/x86/include/asm/numa.h | 7 ------- arch/x86/mm/numa.c | 7 ------- 2 files changed, 14 deletions(-)
diff --git a/arch/x86/include/asm/numa.h b/arch/x86/include/asm/numa.h index e3bae2b60a0db..ef2844d691735 100644 --- a/arch/x86/include/asm/numa.h +++ b/arch/x86/include/asm/numa.h @@ -12,13 +12,6 @@
#define NR_NODE_MEMBLKS (MAX_NUMNODES*2)
-/* - * Too small node sizes may confuse the VM badly. Usually they - * result from BIOS bugs. So dont recognize nodes as standalone - * NUMA entities that have less than this amount of RAM listed: - */ -#define NODE_MIN_SIZE (4*1024*1024) - extern int numa_off;
/* diff --git a/arch/x86/mm/numa.c b/arch/x86/mm/numa.c index e360c6892a584..1a1c0c242f272 100644 --- a/arch/x86/mm/numa.c +++ b/arch/x86/mm/numa.c @@ -601,13 +601,6 @@ static int __init numa_register_memblks(struct numa_meminfo *mi) if (start >= end) continue;
- /* - * Don't confuse VM with a node that doesn't have the - * minimum amount of memory: - */ - if (end && (end - start) < NODE_MIN_SIZE) - continue; - alloc_node_data(nid); }