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=-3.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS autolearn=no 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 7EA85C2D0EC for ; Fri, 27 Mar 2020 03:27:18 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 6036820714 for ; Fri, 27 Mar 2020 03:27:18 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727708AbgC0D1Q (ORCPT ); Thu, 26 Mar 2020 23:27:16 -0400 Received: from shards.monkeyblade.net ([23.128.96.9]:58054 "EHLO shards.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726363AbgC0D1Q (ORCPT ); Thu, 26 Mar 2020 23:27:16 -0400 Received: from localhost (unknown [IPv6:2601:601:9f00:477::3d5]) (using TLSv1 with cipher AES256-SHA (256/256 bits)) (Client did not present a certificate) (Authenticated sender: davem-davemloft) by shards.monkeyblade.net (Postfix) with ESMTPSA id 0591D15CE962A; Thu, 26 Mar 2020 20:27:14 -0700 (PDT) Date: Thu, 26 Mar 2020 20:27:14 -0700 (PDT) Message-Id: <20200326.202714.1221436401038064762.davem@davemloft.net> To: cai@lca.pw Cc: kuznet@ms2.inr.ac.ru, yoshfuji@linux-ipv6.org, kuba@kernel.org, eric.dumazet@gmail.com, netdev@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v2] ipv4: fix a RCU-list lock in fib_triestat_seq_show From: David Miller In-Reply-To: <20200325220100.7863-1-cai@lca.pw> References: <20200325220100.7863-1-cai@lca.pw> X-Mailer: Mew version 6.8 on Emacs 26.1 Mime-Version: 1.0 Content-Type: Text/Plain; charset=us-ascii Content-Transfer-Encoding: 7bit X-Greylist: Sender succeeded SMTP AUTH, not delayed by milter-greylist-4.5.12 (shards.monkeyblade.net [149.20.54.216]); Thu, 26 Mar 2020 20:27:15 -0700 (PDT) Sender: netdev-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org From: Qian Cai Date: Wed, 25 Mar 2020 18:01:00 -0400 > fib_triestat_seq_show() calls hlist_for_each_entry_rcu(tb, head, > tb_hlist) without rcu_read_lock() will trigger a warning, > > net/ipv4/fib_trie.c:2579 RCU-list traversed in non-reader section!! > > other info that might help us debug this: > > rcu_scheduler_active = 2, debug_locks = 1 > 1 lock held by proc01/115277: > #0: c0000014507acf00 (&p->lock){+.+.}-{3:3}, at: seq_read+0x58/0x670 > > Call Trace: > dump_stack+0xf4/0x164 (unreliable) > lockdep_rcu_suspicious+0x140/0x164 > fib_triestat_seq_show+0x750/0x880 > seq_read+0x1a0/0x670 > proc_reg_read+0x10c/0x1b0 > __vfs_read+0x3c/0x70 > vfs_read+0xac/0x170 > ksys_read+0x7c/0x140 > system_call+0x5c/0x68 > > Fix it by adding a pair of rcu_read_lock/unlock() and use > cond_resched_rcu() to avoid the situation where walking of a large > number of items may prevent scheduling for a long time. > > Signed-off-by: Qian Cai Eric, please review.