From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754806AbaDWB7T (ORCPT ); Tue, 22 Apr 2014 21:59:19 -0400 Received: from mail-pd0-f170.google.com ([209.85.192.170]:43909 "EHLO mail-pd0-f170.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751688AbaDWB7R (ORCPT ); Tue, 22 Apr 2014 21:59:17 -0400 Date: Tue, 22 Apr 2014 18:59:15 -0700 (PDT) From: David Rientjes X-X-Sender: rientjes@chino.kir.corp.google.com To: Peter Zijlstra cc: Andrew Morton , Jiang Liu , Ingo Molnar , Ingo Molnar , "Rafael J . Wysocki" , Tony Luck , linux-kernel@vger.kernel.org Subject: Re: [Bugfix] sched: fix possible invalid memory access caused by CPU hot-addition In-Reply-To: <20140422200449.GF11096@twins.programming.kicks-ass.net> Message-ID: References: <1398144435-26271-1-git-send-email-jiang.liu@linux.intel.com> <20140422081515.GF11182@twins.programming.kicks-ass.net> <20140422130151.83bc4539364ca660c68de859@linux-foundation.org> <20140422200449.GF11096@twins.programming.kicks-ass.net> User-Agent: Alpine 2.02 (DEB 1266 2009-07-14) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 22 Apr 2014, Peter Zijlstra wrote: > On Tue, Apr 22, 2014 at 01:01:51PM -0700, Andrew Morton wrote: > > On Tue, 22 Apr 2014 10:15:15 +0200 Peter Zijlstra wrote: > > > > > On Tue, Apr 22, 2014 at 01:27:15PM +0800, Jiang Liu wrote: > > > > When calling kzalloc_node(size, flags, node), we should first check > > > > whether node is onlined, otherwise it may cause invalid memory access > > > > as below. > > > > > > But this is only for memory less node crap, right? > > > > um, why are memoryless nodes crap? > > Why wouldn't they be? Having CPUs with no local memory seems decidedly > suboptimal. The quick fix for memoryless node issues is usually just do cpu_to_mem() rather than cpu_to_node() in the caller. This assumes that the arch is setup correctly to handle memoryless nodes with CONFIG_HAVE_MEMORYLESS_NODES (and we've had problems recently with memoryless nodes not being configured correctly on powerpc). That type of a fix would probably be better handled in the slab allocator, though, since kmalloc_node(nid) shouldn't crash just because nid is memoryless, we should be doing local_memory_node(node) when allocating the slab pages. However, I don't think memoryless nodes are the problem here since Jiang is testing for !node_online(nid) in his patch, so it's a problem with cpu_to_node() pointing to an offline node. It makes sense for the page allocator to crash in such a case, the node id is erroneous. So either the cpu-to-node mapping is invalid or alloc_fair_sched_group() is allocating memory for a cpu on an offline node. The for_each_possible_cpu() looks suspicious. There's no guarantee that local_memory_node(node) for an offline node will return anything with affinity, so falling back to NUMA_NO_NODE looks appropriate in Jiang's patch.