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=-17.0 required=3.0 tests=BAYES_00,INCLUDES_CR_TRAILER, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_GIT 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 DB9B4C352B3 for ; Sun, 20 Dec 2020 03:39:20 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id B574F23A9B for ; Sun, 20 Dec 2020 03:39:20 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727560AbgLTDgA (ORCPT ); Sat, 19 Dec 2020 22:36:00 -0500 Received: from mail.kernel.org ([198.145.29.99]:57982 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726953AbgLTDf5 (ORCPT ); Sat, 19 Dec 2020 22:35:57 -0500 From: Sasha Levin Authentication-Results: mail.kernel.org; dkim=permerror (bad message/signature format) To: linux-kernel@vger.kernel.org, stable@vger.kernel.org Cc: Dongdong Wang , Alexei Starovoitov , Cong Wang , Sasha Levin , netdev@vger.kernel.org, bpf@vger.kernel.org Subject: [PATCH AUTOSEL 5.9 06/15] lwt: Disable BH too in run_lwt_bpf() Date: Sat, 19 Dec 2020 22:34:24 -0500 Message-Id: <20201220033434.2728348-6-sashal@kernel.org> X-Mailer: git-send-email 2.27.0 In-Reply-To: <20201220033434.2728348-1-sashal@kernel.org> References: <20201220033434.2728348-1-sashal@kernel.org> MIME-Version: 1.0 X-stable: review X-Patchwork-Hint: Ignore Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Dongdong Wang [ Upstream commit d9054a1ff585ba01029584ab730efc794603d68f ] The per-cpu bpf_redirect_info is shared among all skb_do_redirect() and BPF redirect helpers. Callers on RX path are all in BH context, disabling preemption is not sufficient to prevent BH interruption. In production, we observed strange packet drops because of the race condition between LWT xmit and TC ingress, and we verified this issue is fixed after we disable BH. Although this bug was technically introduced from the beginning, that is commit 3a0af8fd61f9 ("bpf: BPF for lightweight tunnel infrastructure"), at that time call_rcu() had to be call_rcu_bh() to match the RCU context. So this patch may not work well before RCU flavor consolidation has been completed around v5.0. Update the comments above the code too, as call_rcu() is now BH friendly. Signed-off-by: Dongdong Wang Signed-off-by: Alexei Starovoitov Reviewed-by: Cong Wang Link: https://lore.kernel.org/bpf/20201205075946.497763-1-xiyou.wangcong@gmail.com Signed-off-by: Sasha Levin --- net/core/lwt_bpf.c | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-) diff --git a/net/core/lwt_bpf.c b/net/core/lwt_bpf.c index 7d3438215f32c..4f3cb7c15ddfe 100644 --- a/net/core/lwt_bpf.c +++ b/net/core/lwt_bpf.c @@ -39,12 +39,11 @@ static int run_lwt_bpf(struct sk_buff *skb, struct bpf_lwt_prog *lwt, { int ret; - /* Preempt disable is needed to protect per-cpu redirect_info between - * BPF prog and skb_do_redirect(). The call_rcu in bpf_prog_put() and - * access to maps strictly require a rcu_read_lock() for protection, - * mixing with BH RCU lock doesn't work. + /* Preempt disable and BH disable are needed to protect per-cpu + * redirect_info between BPF prog and skb_do_redirect(). */ preempt_disable(); + local_bh_disable(); bpf_compute_data_pointers(skb); ret = bpf_prog_run_save_cb(lwt->prog, skb); @@ -78,6 +77,7 @@ static int run_lwt_bpf(struct sk_buff *skb, struct bpf_lwt_prog *lwt, break; } + local_bh_enable(); preempt_enable(); return ret; -- 2.27.0