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Commitd49004c5f0("arch, mm: consolidate initialization of nodes, zones and memory map") moved free_area_init() from setup_arch() to mm_core_init_early(), which runs after setup_arch() returns. This changed the ordering relative to init_cpu_to_node() on x86. Before the commit, free_area_init() ran during paging_init() (called from setup_arch()) *before* init_cpu_to_node(). After the commit, it runs *after* init_cpu_to_node(). On machines with memoryless NUMA nodes (e.g., node 0 has CPUs but no memory), this causes a NULL pointer dereference: 1. numa_register_nodes() skips memoryless nodes: no alloc_node_data() and no node_set_online() for them. 2. init_cpu_to_node() sets memoryless nodes online (they have CPUs) but does not allocate NODE_DATA. 3. free_area_init() checks "if (!node_online(nid))" to decide whether to call alloc_offline_node_data(). Since the memoryless node is now online, the allocation is skipped, leaving NODE_DATA(nid) == NULL. 4. The immediate "pgdat = NODE_DATA(nid)" dereferences NULL. The crash happens before console_init(), so no output is visible without earlyprintk. With earlyprintk enabled, the following panic is observed: BUG: unable to handle page fault for address: 000000000002a1e0 Oops: Oops: 0000 [#1] SMP NOPTI RIP: 0010:free_area_init_node+0x3a/0x540 Call Trace: <TASK> free_area_init+0x331/0x4e0 start_kernel+0x69/0x4a0 x86_64_start_reservations+0x24/0x30 x86_64_start_kernel+0x125/0x130 common_startup_64+0x13e/0x148 </TASK> Kernel panic - not syncing: Attempted to kill the idle task! Fix this by checking "if (!NODE_DATA(nid))" instead of "if (!node_online(nid))". This directly tests whether the per-node data structure needs to be allocated, regardless of the node's online status. This change is also safe for non-x86 architectures as they all allocate NODE_DATA for every node including memoryless ones, so the check simply evaluates to false with no change in behavior. Link: https://lkml.kernel.org/r/20260222115702.3659-1-ming.lei@redhat.com Fixes:d49004c5f0("arch, mm: consolidate initialization of nodes, zones and memory map") Signed-off-by: Ming Lei <ming.lei@redhat.com> Reviewed-by: Mike Rapoport (Microsoft) <rppt@kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Linux kernel ============ The Linux kernel is the core of any Linux operating system. It manages hardware, system resources, and provides the fundamental services for all other software. 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