From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1030213AbeBNMsM (ORCPT ); Wed, 14 Feb 2018 07:48:12 -0500 Received: from mx3-rdu2.redhat.com ([66.187.233.73]:58646 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S967589AbeBNMsK (ORCPT ); Wed, 14 Feb 2018 07:48:10 -0500 Subject: Re: WARNING in kvmalloc_node To: Jesper Dangaard Brouer , Daniel Borkmann 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: Jason Wang Message-ID: Date: Wed, 14 Feb 2018 20:47:56 +0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.6.0 MIME-Version: 1.0 In-Reply-To: <20180214132950.2d06e612@redhat.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit Content-Language: en-US Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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? Thanks