On Mon, Feb 13, 2023 at 09:47:43AM +0100, Vlastimil Babka wrote: > On 2/12/23 12:03, Qi Zheng wrote: > > In x86, numa_register_memblks() is only interested in > > those nodes which have enough memory, so it skips over > > all nodes with memory below NODE_MIN_SIZE (treated as > > a memoryless node). Later on, we will initialize these > > memoryless nodes (allocate pgdat in free_area_init() > > and build zonelist etc), and will online these nodes > > in init_cpu_to_node() and init_gi_nodes(). > > > > After boot, these memoryless nodes are in N_ONLINE > > state but not in N_MEMORY state. But we can still allocate > > pages from these memoryless nodes. > > > > In SLUB, we only process nodes in the N_MEMORY state, > > such as allocating their struct kmem_cache_node. So if > > we allocate a page from the memoryless node above to > > SLUB, the struct kmem_cache_node of the node corresponding > > to this page is NULL, which will cause panic. > > > > 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: > > > > [ 0.149844] BUG: kernel NULL pointer dereference, address: 0000000000000000 > > [ 0.150783] #PF: supervisor write access in kernel mode > > [ 0.151488] #PF: error_code(0x0002) - not-present page > > <...> > > [ 0.156056] RIP: 0010:_raw_spin_lock_irqsave+0x22/0x40 > > <...> > > [ 0.169781] Call Trace: > > [ 0.170159] <TASK> > > [ 0.170448] deactivate_slab+0x187/0x3c0 > > [ 0.171031] ? bootstrap+0x1b/0x10e > > [ 0.171559] ? preempt_count_sub+0x9/0xa0 > > [ 0.172145] ? kmem_cache_alloc+0x12c/0x440 > > [ 0.172735] ? bootstrap+0x1b/0x10e > > [ 0.173236] bootstrap+0x6b/0x10e > > [ 0.173720] kmem_cache_init+0x10a/0x188 > > [ 0.174240] start_kernel+0x415/0x6ac > > [ 0.174738] secondary_startup_64_no_verify+0xe0/0xeb > > [ 0.175417] </TASK> > > [ 0.175713] Modules linked in: > > [ 0.176117] CR2: 0000000000000000 > > > > In addition, we can also encountered this panic in the actual > > production environment. We set up a 2c2g container with two > > numa nodes, and then reserved 128M for kdump, and then we > > can encountered the above panic in the kdump kernel. > > > > To fix it, we can filter memoryless nodes when allocating > > pages. > > > > Signed-off-by: Qi Zheng <zhengqi.arch@xxxxxxxxxxxxx> > > Reported-by: Teng Hu <huteng.ht@xxxxxxxxxxxxx> > > Well AFAIK the key mechanism to only allocate from "good" nodes is the > zonelist, we shouldn't need to start putting extra checks like this. So it > seems to me that the code building the zonelists should take the > NODE_MIN_SIZE constraint in mind. Why just not drop the memory for nodes with size < NODE_MIN_SIZE from memblock at the first place? Then we won't need runtime checks at all. > > --- > > mm/page_alloc.c | 5 +++++ > > 1 file changed, 5 insertions(+) > > > > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > > index 588555754601..b9cce56f4e21 100644 > > --- a/mm/page_alloc.c > > +++ b/mm/page_alloc.c > > @@ -4188,6 +4188,11 @@ get_page_from_freelist(gfp_t gfp_mask, unsigned int order, int alloc_flags, > > (alloc_flags & ALLOC_CPUSET) && > > !__cpuset_zone_allowed(zone, gfp_mask)) > > continue; > > + > > + /* Don't allocate page from memoryless nodes. */ > > + if (!node_state((zone_to_nid(zone)), N_MEMORY)) > > + continue; > > + > > /* > > * When allocating a page cache page for writing, we > > * want to get it from a node that is within its dirty > -- Sincerely yours, Mike.
