On 2/13/23 12:00, Qi Zheng wrote:
>
>
> On 2023/2/13 16:47, 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.
>
> Indeed. How about the following patch:
+Cc also David, forgot earlier.
Looks good to me, at least.
> @@ -6382,8 +6378,11 @@ int find_next_best_node(int node, nodemask_t
> *used_node_mask)
> int min_val = INT_MAX;
> int best_node = NUMA_NO_NODE;
>
> - /* Use the local node if we haven't already */
> - if (!node_isset(node, *used_node_mask)) {
> + /*
> + * Use the local node if we haven't already. But for memoryless
> local
> + * node, we should skip it and fallback to other nodes.
> + */
> + if (!node_isset(node, *used_node_mask) && node_state(node,
> N_MEMORY)) {
> node_set(node, *used_node_mask);
> return node;
> }
>
> For memoryless node, we skip it and fallback to other nodes when
> build its zonelists.
>
> Say we have node0 and node1, and node0 is memoryless, then:
>
> [ 0.102400] Fallback order for Node 0: 1
> [ 0.102931] Fallback order for Node 1: 1
>
> In this way, we will not allocate pages from memoryless node0.
>
>>
>>> ---
>>> 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
>>
>
