From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from shards.monkeyblade.net ([184.105.139.130]:50426 "EHLO shards.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750776AbeBVSuE (ORCPT ); Thu, 22 Feb 2018 13:50:04 -0500 Date: Thu, 22 Feb 2018 13:49:59 -0500 (EST) Message-Id: <20180222.134959.2076675690484053707.davem@davemloft.net> To: yhs@fb.com Cc: ast@fb.com, daniel@iogearbox.net, edumazet@google.com, netdev@vger.kernel.org, kernel-team@fb.com Subject: Re: [PATCH bpf v2] bpf: fix rcu lockdep warning for lpm_trie map_free callback From: David Miller In-Reply-To: <20180222181035.2163332-1-yhs@fb.com> References: <20180222181035.2163332-1-yhs@fb.com> Mime-Version: 1.0 Content-Type: Text/Plain; charset=us-ascii Content-Transfer-Encoding: 7bit Sender: netdev-owner@vger.kernel.org List-ID: From: Yonghong Song Date: Thu, 22 Feb 2018 10:10:35 -0800 > Commit 9a3efb6b661f ("bpf: fix memory leak in lpm_trie map_free callback function") > fixed a memory leak and removed unnecessary locks in map_free callback function. > Unfortrunately, it introduced a lockdep warning. When lockdep checking is turned on, > running tools/testing/selftests/bpf/test_lpm_map will have: > > [ 98.294321] ============================= > [ 98.294807] WARNING: suspicious RCU usage > [ 98.295359] 4.16.0-rc2+ #193 Not tainted > [ 98.295907] ----------------------------- > [ 98.296486] /home/yhs/work/bpf/kernel/bpf/lpm_trie.c:572 suspicious rcu_dereference_check() usage! > [ 98.297657] > [ 98.297657] other info that might help us debug this: > [ 98.297657] > [ 98.298663] > [ 98.298663] rcu_scheduler_active = 2, debug_locks = 1 > [ 98.299536] 2 locks held by kworker/2:1/54: > [ 98.300152] #0: ((wq_completion)"events"){+.+.}, at: [<00000000196bc1f0>] process_one_work+0x157/0x5c0 > [ 98.301381] #1: ((work_completion)(&map->work)){+.+.}, at: [<00000000196bc1f0>] process_one_work+0x157/0x5c0 > > Since actual trie tree removal happens only after no other > accesses to the tree are possible, replacing > rcu_dereference_protected(*slot, lockdep_is_held(&trie->lock)) > with > rcu_dereference_protected(*slot, 1) > fixed the issue. > > Fixes: 9a3efb6b661f ("bpf: fix memory leak in lpm_trie map_free callback function") > Reported-by: Eric Dumazet > Suggested-by: Eric Dumazet > Signed-off-by: Yonghong Song Acked-by: David S. Miller