From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1030374AbeBNN3g (ORCPT ); Wed, 14 Feb 2018 08:29:36 -0500 Received: from www62.your-server.de ([213.133.104.62]:37492 "EHLO www62.your-server.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1030209AbeBNN3d (ORCPT ); Wed, 14 Feb 2018 08:29:33 -0500 Subject: Re: WARNING in kvmalloc_node To: Jason Wang , Jesper Dangaard Brouer Cc: Michal Hocko , Matthew Wilcox , syzbot , akpm@linux-foundation.org, dhowells@redhat.com, hannes@cmpxchg.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, mingo@kernel.org, rppt@linux.vnet.ibm.com, syzkaller-bugs@googlegroups.com, vbabka@suse.cz, viro@zeniv.linux.org.uk, Alexei Starovoitov , netdev@vger.kernel.org, "Michael S. Tsirkin" References: <001a1144c4ca5dc9d6056520c7b7@google.com> <20180214025533.GA28811@bombadil.infradead.org> <20180214084308.GX3443@dhcp22.suse.cz> <24351362-a099-3317-2b96-8cdc6835eb1e@redhat.com> <20180214115119.GA3443@dhcp22.suse.cz> <62489a86-b578-b075-3ada-c2f5baf5b787@redhat.com> <20180214132950.2d06e612@redhat.com> From: Daniel Borkmann Message-ID: <0c511cb9-9f3c-eb58-9d33-e4fc873b26a3@iogearbox.net> Date: Wed, 14 Feb 2018 14:29:23 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.3.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit X-Authenticated-Sender: daniel@iogearbox.net Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 02/14/2018 01:47 PM, Jason Wang wrote: > On 2018年02月14日 20:29, Jesper Dangaard Brouer wrote: >> On Wed, 14 Feb 2018 13:17:18 +0100 >> Daniel Borkmann wrote: >>> On 02/14/2018 01:02 PM, Jason Wang wrote: >>>> On 2018年02月14日 19:51, Michal Hocko wrote: >>>>> On Wed 14-02-18 19:47:30, Jason Wang wrote: >>>>>> On 2018年02月14日 17:28, Daniel Borkmann wrote: >>>>>>> [ +Jason, +Jesper ] >>>>>>> >>>>>>> On 02/14/2018 09:43 AM, Michal Hocko wrote: >>>>>>>> On Tue 13-02-18 18:55:33, Matthew Wilcox wrote: >>>>>>>>> On Tue, Feb 13, 2018 at 03:59:01PM -0800, syzbot wrote: >>>>>>>> [...] >>>>>>>>>>     kvmalloc include/linux/mm.h:541 [inline] >>>>>>>>>>     kvmalloc_array include/linux/mm.h:557 [inline] >>>>>>>>>>     __ptr_ring_init_queue_alloc include/linux/ptr_ring.h:474 [inline] >>>>>>>>>>     ptr_ring_init include/linux/ptr_ring.h:492 [inline] >>>>>>>>>>     __cpu_map_entry_alloc kernel/bpf/cpumap.c:359 [inline] >>>>>>>>>>     cpu_map_update_elem+0x3c3/0x8e0 kernel/bpf/cpumap.c:490 >>>>>>>>>>     map_update_elem kernel/bpf/syscall.c:698 [inline] >>>>>>>>> Blame the BPF people, not the MM people ;-) >>>>>>> Heh, not really. ;-) >>>>>>>   >>>>>>>> Yes. kvmalloc (the vmalloc part) doesn't support GFP_ATOMIC semantic. >>>>>>> Agree, that doesn't work. >>>>>>> >>>>>>> Bug was added in commit 0bf7800f1799 ("ptr_ring: try vmalloc() when kmalloc() fails"). >>>>>>> >>>>>>> Jason, please take a look at fixing this, thanks! >>>>>> It looks to me the only solution is to revert that commit. >>>>> Do you really need this to be GFP_ATOMIC? I can see some callers are >>>>> under RCU read lock but can we perhaps do the allocation outside of this >>>>> section? >>>> If I understand the code correctly, the code would be called by XDP program (usually run inside a bh) which makes it hard to do this. >>>> >>>> Rethink of this, we can probably test gfp and not call kvmalloc if GFP_ATOMIC is set in __ptr_ring_init_queue_alloc(). >>> That would be one option indeed (probably useful in any case to make the API >>> more robust). Another one is to just not use GFP_ATOMIC in cpumap. Looking at >>> it, update can neither be called out of a BPF prog since prevented by verifier >>> nor under RCU reader side when updating this type of map from syscall path. >>> Jesper, any concrete reason we still need GFP_ATOMIC here? >> Allocations in cpumap (related to ptr_ring) should only be possible to >> be initiated through userspace via bpf-syscall. > > I see verifier guarantees this. > >>   Thus, there isn't any >> reason for GFP_ATOMIC here. > > Want me to send a patch to remove GFP_ATOMIC here? Sounds good, thanks Jason!