From mboxrd@z Thu Jan 1 00:00:00 1970 From: Alexei Starovoitov Subject: Re: [PATCH net] net/xdp: Fix suspicious RCU usage warning Date: Tue, 17 Jul 2018 09:47:28 -0700 Message-ID: <20180717164726.ommc2ddosha6zl6d@ast-mbp> References: <1531840238-30818-1-git-send-email-tariqt@mellanox.com> <1531840238-30818-2-git-send-email-tariqt@mellanox.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: "David S. Miller" , netdev@vger.kernel.org, Eran Ben Elisha , Jesper Dangaard Brouer To: Tariq Toukan Return-path: Received: from mail-pf0-f195.google.com ([209.85.192.195]:42090 "EHLO mail-pf0-f195.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729669AbeGQRVC (ORCPT ); Tue, 17 Jul 2018 13:21:02 -0400 Received: by mail-pf0-f195.google.com with SMTP id l9-v6so779535pff.9 for ; Tue, 17 Jul 2018 09:47:31 -0700 (PDT) Content-Disposition: inline In-Reply-To: <1531840238-30818-2-git-send-email-tariqt@mellanox.com> Sender: netdev-owner@vger.kernel.org List-ID: On Tue, Jul 17, 2018 at 06:10:38PM +0300, Tariq Toukan wrote: > Fix the warning below by calling rhashtable_lookup under > RCU read lock. > > [ 342.450870] WARNING: suspicious RCU usage > [ 342.455856] 4.18.0-rc2+ #17 Tainted: G O > [ 342.462210] ----------------------------- > [ 342.467202] ./include/linux/rhashtable.h:481 suspicious rcu_dereference_check() usage! > [ 342.476568] > [ 342.476568] other info that might help us debug this: > [ 342.476568] > [ 342.486978] > [ 342.486978] rcu_scheduler_active = 2, debug_locks = 1 > [ 342.495211] 4 locks held by modprobe/3934: > [ 342.500265] #0: 00000000e23116b2 (mlx5_intf_mutex){+.+.}, at: > mlx5_unregister_interface+0x18/0x90 [mlx5_core] > [ 342.511953] #1: 00000000ca16db96 (rtnl_mutex){+.+.}, at: unregister_netdev+0xe/0x20 > [ 342.521109] #2: 00000000a46e2c4b (&priv->state_lock){+.+.}, at: mlx5e_close+0x29/0x60 > [mlx5_core] > [ 342.531642] #3: 0000000060c5bde3 (mem_id_lock){+.+.}, at: xdp_rxq_info_unreg+0x93/0x6b0 > [ 342.541206] > [ 342.541206] stack backtrace: > [ 342.547075] CPU: 12 PID: 3934 Comm: modprobe Tainted: G O 4.18.0-rc2+ #17 > [ 342.556621] Hardware name: Dell Inc. PowerEdge R730/0H21J3, BIOS 1.5.4 10/002/2015 > [ 342.565606] Call Trace: > [ 342.568861] dump_stack+0x78/0xb3 > [ 342.573086] xdp_rxq_info_unreg+0x3f5/0x6b0 > [ 342.578285] ? __call_rcu+0x220/0x300 > [ 342.582911] mlx5e_free_rq+0x38/0xc0 [mlx5_core] > [ 342.588602] mlx5e_close_channel+0x20/0x120 [mlx5_core] > [ 342.594976] mlx5e_close_channels+0x26/0x40 [mlx5_core] > [ 342.601345] mlx5e_close_locked+0x44/0x50 [mlx5_core] > [ 342.607519] mlx5e_close+0x42/0x60 [mlx5_core] > [ 342.613005] __dev_close_many+0xb1/0x120 > [ 342.617911] dev_close_many+0xa2/0x170 > [ 342.622622] rollback_registered_many+0x148/0x460 > [ 342.628401] ? __lock_acquire+0x48d/0x11b0 > [ 342.633498] ? unregister_netdev+0xe/0x20 > [ 342.638495] rollback_registered+0x56/0x90 > [ 342.643588] unregister_netdevice_queue+0x7e/0x100 > [ 342.649461] unregister_netdev+0x18/0x20 > [ 342.654362] mlx5e_remove+0x2a/0x50 [mlx5_core] > [ 342.659944] mlx5_remove_device+0xe5/0x110 [mlx5_core] > [ 342.666208] mlx5_unregister_interface+0x39/0x90 [mlx5_core] > [ 342.673038] cleanup+0x5/0xbfc [mlx5_core] > [ 342.678094] __x64_sys_delete_module+0x16b/0x240 > [ 342.683725] ? do_syscall_64+0x1c/0x210 > [ 342.688476] do_syscall_64+0x5a/0x210 > [ 342.693025] entry_SYSCALL_64_after_hwframe+0x49/0xbe > > Fixes: 8d5d88527587 ("xdp: rhashtable with allocator ID to pointer mapping") > Signed-off-by: Tariq Toukan > Cc: Jesper Dangaard Brouer > --- > net/core/xdp.c | 2 ++ > 1 file changed, 2 insertions(+) > > diff --git a/net/core/xdp.c b/net/core/xdp.c > index 9d1f22072d5d..c20fefbfb76c 100644 > --- a/net/core/xdp.c > +++ b/net/core/xdp.c > @@ -102,7 +102,9 @@ static void __xdp_rxq_info_unreg_mem_model(struct xdp_rxq_info *xdp_rxq) > > mutex_lock(&mem_id_lock); > > + rcu_read_lock(); > xa = rhashtable_lookup(mem_id_ht, &id, mem_id_rht_params); > + rcu_read_unlock(); > if (!xa) { if it's an actual bug rcu_read_unlock seems to be misplaced. It silences the warn, but rcu section looks wrong.