From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wr0-f198.google.com (mail-wr0-f198.google.com [209.85.128.198]) by kanga.kvack.org (Postfix) with ESMTP id 68CA86B0008 for ; Wed, 14 Feb 2018 16:24:16 -0500 (EST) Received: by mail-wr0-f198.google.com with SMTP id i12so661146wra.22 for ; Wed, 14 Feb 2018 13:24:16 -0800 (PST) Received: from www62.your-server.de (www62.your-server.de. [213.133.104.62]) by mx.google.com with ESMTPS id o199si679654wmd.268.2018.02.14.05.29.33 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 14 Feb 2018 05:29:33 -0800 (PST) Subject: Re: WARNING in kvmalloc_node 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 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Sender: owner-linux-mm@kvack.org List-ID: 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" On 02/14/2018 01:47 PM, Jason Wang wrote: > On 2018a1'02ae??14ae?JPY 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 2018a1'02ae??14ae?JPY 19:51, Michal Hocko wrote: >>>>> On Wed 14-02-18 19:47:30, Jason Wang wrote: >>>>>> On 2018a1'02ae??14ae?JPY 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: >>>>>>>> [...] >>>>>>>>>> A A A kvmalloc include/linux/mm.h:541 [inline] >>>>>>>>>> A A A kvmalloc_array include/linux/mm.h:557 [inline] >>>>>>>>>> A A A __ptr_ring_init_queue_alloc include/linux/ptr_ring.h:474 [inline] >>>>>>>>>> A A A ptr_ring_init include/linux/ptr_ring.h:492 [inline] >>>>>>>>>> A A A __cpu_map_entry_alloc kernel/bpf/cpumap.c:359 [inline] >>>>>>>>>> A A A cpu_map_update_elem+0x3c3/0x8e0 kernel/bpf/cpumap.c:490 >>>>>>>>>> A A A map_update_elem kernel/bpf/syscall.c:698 [inline] >>>>>>>>> Blame the BPF people, not the MM people ;-) >>>>>>> Heh, not really. ;-) >>>>>>> A >>>>>>>> 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. > >> A 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! -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org