From nobody Fri Apr 17 07:44:20 2026 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 36CFC2BD11 for ; Sun, 22 Feb 2026 11:57:17 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=170.10.129.124 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1771761438; cv=none; b=OPSteAqndd8UwaFl5Dulc0006s3h6DV6jGfo0BH0il6kRQFKJIGay0lEjBroUqYGVyeitIuXe6OgNlG3XHchgAsR58lTBP719bWwUrZ2Qy7BKx8Mdp4zHVK+rZpOfeMKX1DUkg0sdFgEJLOlDtQNSdkI7x1QWWle2a0YXYnvrlA= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1771761438; c=relaxed/simple; bh=s6aWFFx5x3xIyOnQOnD3FXuudun9p7vb/9ppK1xF/ck=; h=From:To:Cc:Subject:Date:Message-ID:MIME-Version; b=kGBw8FF8HYvB3sYxPpE93l+eSz/idr5qZyOh+dkXM7dzOvBZX/aIA13X0QFpHf88EpjPg9CsGbScNF8XLjL2D3E7dBAISpKRS6VM28MwB5Uaq85j/4j6WjoeS9iDdlShc6OKn2QeKRiSg04Ov7sWpkZWN19ifmap2YssohRx9Cg= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=redhat.com; spf=pass smtp.mailfrom=redhat.com; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b=JiqED5ii; arc=none smtp.client-ip=170.10.129.124 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=redhat.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=redhat.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="JiqED5ii" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1771761434; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding; bh=uD8Q34JvjH8pMvt8PCVjIF4RUIZtweGW5/Eb5+0FOc4=; b=JiqED5iiuA8nPPf2asjVvqlxCo0BiejPocjyvVJ0YGxur5DDOjlAcJbQ5rF9m2gWjdCNbG 8ZvpB7aJAcVcsJkFuxRBzedYF8NlVH4Zo3PR2zsjdXhUPF7L2tCslxOThjlzm+6iNhwG2s 45QMh7f2iBxyPw9bCbxtaZrIAa4RHzQ= Received: from mx-prod-mc-01.mail-002.prod.us-west-2.aws.redhat.com (ec2-54-186-198-63.us-west-2.compute.amazonaws.com [54.186.198.63]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-325-6iNyqwtzN66KrTi__tukeA-1; Sun, 22 Feb 2026 06:57:11 -0500 X-MC-Unique: 6iNyqwtzN66KrTi__tukeA-1 X-Mimecast-MFC-AGG-ID: 6iNyqwtzN66KrTi__tukeA_1771761430 Received: from mx-prod-int-03.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-03.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.12]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mx-prod-mc-01.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id DD4121956095; Sun, 22 Feb 2026 11:57:09 +0000 (UTC) Received: from localhost (unknown [10.72.116.32]) by mx-prod-int-03.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTP id 7D7B719560A7; Sun, 22 Feb 2026 11:57:07 +0000 (UTC) From: Ming Lei To: Andrew Morton , linux-mm@kvack.org Cc: linux-kernel@vger.kernel.org, Ming Lei Subject: [PATCH V2] mm: fix NULL NODE_DATA dereference for memoryless nodes on boot Date: Sun, 22 Feb 2026 19:57:02 +0800 Message-ID: <20260222115702.3659-1-ming.lei@redhat.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-Scanned-By: MIMEDefang 3.0 on 10.30.177.12 Content-Type: text/plain; charset="utf-8" Commit d49004c5f0c1 ("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) =3D=3D NULL. 4. The immediate "pgdat =3D 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: 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 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. Fixes: d49004c5f0c1 ("arch, mm: consolidate initialization of nodes, zones = and memory map") Signed-off-by: Ming Lei Reviewed-by: Mike Rapoport (Microsoft) --- V2: - add commit log for non-x86 arch - add comment for code change mm/mm_init.c | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-) diff --git a/mm/mm_init.c b/mm/mm_init.c index 61d983d23f55..df34797691bd 100644 --- a/mm/mm_init.c +++ b/mm/mm_init.c @@ -1896,7 +1896,11 @@ static void __init free_area_init(void) for_each_node(nid) { pg_data_t *pgdat; =20 - if (!node_online(nid)) + /* + * If an architecture has not allocated node data for + * this node, presume the node is memoryless or offline. + */ + if (!NODE_DATA(nid)) alloc_offline_node_data(nid); =20 pgdat =3D NODE_DATA(nid); --=20 2.53.0