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SubjectRe: [PATCH] x86/mm: drop 4MB restriction on minimal NUMA node size
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On 17.10.23 09:28, David Hildenbrand wrote:
> On 17.10.23 08:22, Mike Rapoport wrote:
>> From: "Mike Rapoport (IBM)" <rppt@kernel.org>
>>
>> Qi Zheng reports crashes in a production environment and provides 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:
>>
>> [ 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
>>
>> The crashes happen because of inconsistency between nodemask that has
>> nodes with less than 4MB as memoryless and the actual memory fed into
>> 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.
>>
>> Since then a lot has changed and core mm won't confuse badly about small
>> node sizes.
>>
>> Drop the limitation for the minimal node size.
>>
>> Reported-by: Qi Zheng <zhengqi.arch@bytedance.com>
>> Signed-off-by: Mike Rapoport (IBM) <rppt@kernel.org>
>> Acked-by: David Hildenbrand <david@redhat.com>
>> Acked-by: Michal Hocko <mhocko@suse.com>
>> Link: https://lore.kernel.org/all/20230212110305.93670-1-zhengqi.arch@bytedance.com/
>
> That's just a resend I assume? Or has anything changed?

Saw the other mail now, so just a resend.

--
Cheers,

David / dhildenb

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