Messages in this thread |  | | From | w15303746062@163 ... | | Subject | [BUG] x86/smpboot: WARN_ON in set_cpu_sibling_map triggered by numa=fake=2 | | Date | Wed, 29 Apr 2026 11:41:25 +0800 |
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Hi x86 maintainers,
While fuzzing the v7.0 kernel, I encountered a persistent WARNING in `set_cpu_sibling_map()` during boot when using the `numa=fake=2` command-line parameter.
The issue appears to be a logic gap in the topology consistency check. When `numa=fake=N` is used, it artificially divides a single physical package into multiple software NUMA nodes. However, the existing check in `set_cpu_sibling_map()` does not account for this fake NUMA state:
if (match_pkg(c, o) && !topology_same_node(c, o)) WARN_ON_ONCE(topology_num_nodes_per_package() == 1);
Since `numa=fake` forces `!topology_same_node(c, o)` to be true for CPUs on the same package, the WARN_ON_ONCE is falsely triggered. With `panic_on_warn=1` enabled in many fuzzing and testing environments, this leads to an early boot panic.
Here is the relevant part of the crash log:
------------[ cut here ]------------ WARNING: arch/x86/kernel/smpboot.c:698 at set_cpu_sibling_map+0x1206/0x1f20 Modules linked in: CPU: 1 UID: 0 PID: 0 Comm: swapper/1 Not tainted 7.0.0 #1 PREEMPT(full) Hardware name: QEMU Standard PC (Q35 + ICH9, 2009) RIP: 0010:set_cpu_sibling_map+0x1206/0x1f20 Call Trace: <TASK> ap_starting arch/x86/kernel/smpboot.c:196 [inline] start_secondary+0xd8/0x2d0 arch/x86/kernel/smpboot.c:280 common_startup_64+0x13e/0x148 </TASK> ---[ end trace ]---
I am reporting this to bring it to your attention, as it might require a small adjustment to bypass this strict topology check when `numa=fake` is active.
Best regards, Mingyu Wang
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