From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-8.9 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, MENTIONS_GIT_HOSTING,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 59A0DC2D0CE for ; Tue, 21 Jan 2020 12:42:27 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 246C124653 for ; Tue, 21 Jan 2020 12:42:27 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=cloudflare.com header.i=@cloudflare.com header.b="AuTB3b3I" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728842AbgAUMm0 (ORCPT ); Tue, 21 Jan 2020 07:42:26 -0500 Received: from mail-wr1-f66.google.com ([209.85.221.66]:37207 "EHLO mail-wr1-f66.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727350AbgAUMmZ (ORCPT ); Tue, 21 Jan 2020 07:42:25 -0500 Received: by mail-wr1-f66.google.com with SMTP id w15so3040601wru.4 for ; Tue, 21 Jan 2020 04:42:24 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=cloudflare.com; s=google; h=references:user-agent:from:to:cc:subject:in-reply-to:date :message-id:mime-version; bh=T8LTDpV4SYvFT+svgavRLIeF6WcPBcW9R80yIXDdth8=; b=AuTB3b3IBRqzf+sft2bF0mxHV6glEKpQTbyHppOs+lgLtSI4G7td+0KTO1Dnlk0cFi cGK58ZXaStQFd6QIPzx2Yf5HjgNUsyUUE1K4SM4mMQK8BgKCRQ1wDLnPrdwtb9yoc/bX SlxBdlfaVWye8UdN9cFsF6TDP3GVptX/6Vcvw= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:references:user-agent:from:to:cc:subject :in-reply-to:date:message-id:mime-version; bh=T8LTDpV4SYvFT+svgavRLIeF6WcPBcW9R80yIXDdth8=; b=t8GmS/bWZ22k/+zYMJmL7N+hWrtfV4jFqf9ubkk+3Fo+/IOgKXGDnKa88idqbXA4Ci KMeCxcwku+43Enip46+Gl/etk2CxW87wz9gABHPUIL1JObUPhDBfeRF8XY6aWdjGbPh2 o06Q3k5x313TBCUpb9OZ3FGT3M0HlWi84BRKqajDhYyFWEUe+bw/SVOjcQBfi3GUokFP JUYMAaWkf+NDRCWlMbfuE4AjlT6Gi2z3kUy1eZ4yN0P5KjOLEKNS3DSNheMaZEnL76nu Q8q2gBP5AMR4RnwCqU7x/wGWMYX8QpKMeV1y9pRr8OnnSSzf2wTmXO3IyPJsIkc1EaDl hJHQ== X-Gm-Message-State: APjAAAV1p4Pe0ofmAYWKo79P2AIL5yiplJQe3oIxZ3JZTGlV9ZQuDXfv cznBM5R3vE2nZBJN49N6trLe9A== X-Google-Smtp-Source: APXvYqze9aGSsYl2P1uvmHLfqXt4wmAXuCH59vhyTaBzMT2DbW3oldw81z8aYyxkkEkRlfB8+3/uVQ== X-Received: by 2002:adf:fa12:: with SMTP id m18mr4967629wrr.309.1579610543539; Tue, 21 Jan 2020 04:42:23 -0800 (PST) Received: from cloudflare.com ([176.221.114.230]) by smtp.gmail.com with ESMTPSA id x10sm51573340wrp.58.2020.01.21.04.42.22 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 21 Jan 2020 04:42:22 -0800 (PST) References: <20200110105027.257877-1-jakub@cloudflare.com> <20200110105027.257877-3-jakub@cloudflare.com> <5e1a56e630ee1_1e7f2b0c859c45c0c4@john-XPS-13-9370.notmuch> <87muars890.fsf@cloudflare.com> <5e25dc995d7d_74082aaee6e465b441@john-XPS-13-9370.notmuch> <874kwqroap.fsf@cloudflare.com> User-agent: mu4e 1.1.0; emacs 26.3 From: Jakub Sitnicki To: John Fastabend Cc: bpf@vger.kernel.org, netdev@vger.kernel.org, kernel-team@cloudflare.com, Eric Dumazet , Lorenz Bauer , Martin KaFai Lau Subject: Re: [PATCH bpf-next v2 02/11] net, sk_msg: Annotate lockless access to sk_prot on clone In-reply-to: <874kwqroap.fsf@cloudflare.com> Date: Tue, 21 Jan 2020 13:42:22 +0100 Message-ID: <8736c9rnf5.fsf@cloudflare.com> MIME-Version: 1.0 Content-Type: text/plain Sender: netdev-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On Mon, Jan 20, 2020 at 07:11 PM CET, Jakub Sitnicki wrote: > On Mon, Jan 20, 2020 at 06:00 PM CET, John Fastabend wrote: >> Jakub Sitnicki wrote: >>> On Sun, Jan 12, 2020 at 12:14 AM CET, John Fastabend wrote: >>> > Jakub Sitnicki wrote: >>> >> sk_msg and ULP frameworks override protocol callbacks pointer in >>> >> sk->sk_prot, while TCP accesses it locklessly when cloning the listening >>> >> socket. >>> >> >>> >> Once we enable use of listening sockets with sockmap (and hence sk_msg), >>> >> there can be shared access to sk->sk_prot if socket is getting cloned while >>> >> being inserted/deleted to/from the sockmap from another CPU. Mark the >>> >> shared access with READ_ONCE/WRITE_ONCE annotations. >>> >> >>> >> Signed-off-by: Jakub Sitnicki >>> > >>> > In sockmap side I fixed this by wrapping the access in a lock_sock[0]. So >>> > Do you think this is still needed with that in mind? The bpf_clone call >>> > is using sk_prot_creater and also setting the newsk's proto field. Even >>> > if the listening parent sock was being deleted in parallel would that be >>> > a problem? We don't touch sk_prot_creator from the tear down path. I've >>> > only scanned the 3..11 patches so maybe the answer is below. If that is >>> > the case probably an improved commit message would be helpful. >>> >>> I think it is needed. Not because of tcp_bpf_clone or that we access >>> listener's sk_prot_creator from there, if I'm grasping your question. >>> >>> Either way I'm glad this came up. Let's go though my reasoning and >>> verify it. tcp stack accesses the listener sk_prot while cloning it: >>> >>> tcp_v4_rcv >>> sk = __inet_lookup_skb(...) >>> tcp_check_req(sk) >>> inet_csk(sk)->icsk_af_ops->syn_recv_sock >>> tcp_v4_syn_recv_sock >>> tcp_create_openreq_child >>> inet_csk_clone_lock >>> sk_clone_lock >>> READ_ONCE(sk->sk_prot) >>> >>> It grabs a reference to the listener, but doesn't grab the sk_lock. >>> >>> On another CPU we can be inserting/removing the listener socket from the >>> sockmap and writing to its sk_prot. We have the update and the remove >>> path: >>> >>> sock_map_ops->map_update_elem >>> sock_map_update_elem >>> sock_map_update_common >>> sock_map_link_no_progs >>> tcp_bpf_init >>> tcp_bpf_update_sk_prot >>> sk_psock_update_proto >>> WRITE_ONCE(sk->sk_prot, ops) >>> >>> sock_map_ops->map_delete_elem >>> sock_map_delete_elem >>> __sock_map_delete >>> sock_map_unref >>> sk_psock_put >>> sk_psock_drop >>> sk_psock_restore_proto >>> tcp_update_ulp >>> WRITE_ONCE(sk->sk_prot, proto) >>> >>> Following the guidelines from KTSAN project [0], sk_prot looks like a >>> candidate for annotating it. At least on these 3 call paths. >>> >>> If that sounds correct, I can add it to the patch description. >>> >>> Thanks, >>> -jkbs >>> >>> [0] https://github.com/google/ktsan/wiki/READ_ONCE-and-WRITE_ONCE >> >> Hi Jakub, can push this to bpf tree as well? There is another case >> already in-kernel where this is needed. If the map is removed while >> a recvmsg is in flight. >> >> tcp_bpf_recvmsg() >> psock = sk_psock_get(sk) <- refcnt 2 >> lock_sock(sk); >> ... >> sock_map_free() <- refcnt 1 >> release_sock(sk) >> sk_psock_put() <- refcnt 0 >> >> Then can you add this diff as well I got a bit too carried away >> with that. If your busy I can do it as well if you want. Thanks! > > Hi John, I get the race between map_free and tcp_bpf_recvmsg, and how we > end up dropping psock on a path where we don't hold the sock lock. What > a rare case, since we don't destory maps that often usually. > > However, I'm not sure I follow where shared lockless access to > sk->sk_prot is in this case? > > Perhaps between drop path: > > sk_psock_put > sk_psock_drop > sk_psock_restore_proto > WRITE_ONCE(sk->sk_prot, proto) > > ... and update path where we grab sk_callback_lock a little too late, > that is after updating the proto? > > sock_map_update_common > sock_map_link > tcp_bpf_init > tcp_bpf_update_sk_prot > sk_psock_update_proto > WRITE_ONCE(sk->sk_prot, ops) > > I'm getting v3 ready to post, so happy to help you spin these bits. > I'll need to do it with a fresh head tomorrow, though. > > If I don't see any patches from you hit the ML, I'll split out the > chunks that annotate sk_prot access in sk_psock_{retore,update}_proto > and post them together with the revert you suggested below. I've sent out the partial revert you wanted: https://lore.kernel.org/netdev/20200121123147.706666-1-jakub@cloudflare.com/T/#u But otherwise didn't manage to convince myself that we need to annotate access to sk_prot with READ/WRITE_ONCE in sk_psock_update/restore_proto. Instead, I believe we might need to the extend critical section that grabs sk_callback_lock in sock_map_link over tcp_bpf_init/reinit() to serialize the writers. Unless I'm missing the point here and you had some other race in mind? -jkbs