From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 7DD1034D926 for ; Mon, 23 Feb 2026 11:18:15 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1771845495; cv=none; b=eAwxYZ0MSzQNf+pQiCGlNjf6fQbdBmpNnEoP3YIDhZiTCalT0hgWbHEcIeXmD1ZncoTOxbvEiyUnIHBCTscjeH5ao38FrghT6hlYJDD7X0Xmqv0HoZH8KLEDPwi+x30EtrhpXxGNcYPl7zHpzTmsb4PApKypK2KZJq/ePOTM6QE= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1771845495; c=relaxed/simple; bh=gTMAzkNvvCdzk2jvSyT1hq/hY5rJCtn4E+HGOBjo+ys=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=uGBR48Yqmke4wmxwEazcK21kPkeoUnsxsc3BcuH7tDz7DdZsiFx3wEl58YEnON2nGG/XFbpmLroBPLF8cqZgzRJzgANGdGHhGZWu6qDioUan9UEoZBYbbH2yZWGHBUqqNRvouEAlHCz6bAJ2q44KNxQ3W5z/QYhRtcVcYRRrl5g= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=L9pKHQoL; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="L9pKHQoL" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 6BEB7C116C6; Mon, 23 Feb 2026 11:18:13 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1771845495; bh=gTMAzkNvvCdzk2jvSyT1hq/hY5rJCtn4E+HGOBjo+ys=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=L9pKHQoLD0smM5Y95VqNZA8Dm+zB+CZoNuQysK0Oe0AZTerohXQ4D6ekrtrVWclRh MrHapjS3eoeObS4fEzmR6hd8hCsPPP4hs68ILm/9Xr0SBvB9k4fE89lbrmLY1Gb40t vrncgjMEMRud/WuMRl/Ix8y/CsLxHz/re3yL8boQF6/6YQRNF4U/0N8LKAfzBk0crd 2rNlLaBE+G2pG8yA8y+swOddxu+DRI5lMid18nfOF0yFZrrNR4gGYlHMQRkW3z1Wyi ok8nArgm3j0VLhB6Y2Cf02iL7GvFdbpPpvR9ImHYzA3N251Lv/F45Ek2tp+aEJwT5y 76itplpdzMe6g== Date: Mon, 23 Feb 2026 13:18:09 +0200 From: Mike Rapoport To: Ming Lei Cc: Andrew Morton , linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH V2] mm: fix NULL NODE_DATA dereference for memoryless nodes on boot Message-ID: References: <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-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260222115702.3659-1-ming.lei@redhat.com> On Sun, Feb 22, 2026 at 07:57:02PM +0800, Ming Lei wrote: > 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) == 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: > > 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. This kinda means that x86 does something odd, but that's a matter for additional rework and audit of node allocations. > 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; > > - 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); > > pgdat = NODE_DATA(nid); > -- > 2.53.0 > -- Sincerely yours, Mike.