From mboxrd@z Thu Jan 1 00:00:00 1970 From: John Fastabend Subject: [net-next PATCH] net: rcu lock and preempt disable missing around generic xdp Date: Wed, 16 Aug 2017 11:33:19 -0700 Message-ID: <20170816183319.7709.87749.stgit@john-Precision-Tower-5810> Mime-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Cc: netdev@vger.kernel.org, john.fastabend@gmail.com To: davem@davemloft.net, daniel@iogearbox.net Return-path: Received: from mail-pg0-f66.google.com ([74.125.83.66]:38272 "EHLO mail-pg0-f66.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752038AbdHPSdd (ORCPT ); Wed, 16 Aug 2017 14:33:33 -0400 Received: by mail-pg0-f66.google.com with SMTP id 123so5854775pga.5 for ; Wed, 16 Aug 2017 11:33:33 -0700 (PDT) Sender: netdev-owner@vger.kernel.org List-ID: do_xdp_generic must be called inside rcu critical section with preempt disabled to ensure BPF programs are valid and per-cpu variables used for redirect operations are consistent. This patch ensures this is true and fixes the splat below. The netif_receive_skb_internal() code path is now broken into two rcu critical sections. I decided it was better to limit the preempt_enable/disable block to just the xdp static key portion and the fallout is more rcu_read_lock/unlock calls. Seems like the best option to me. [ 607.596901] ============================= [ 607.596906] WARNING: suspicious RCU usage [ 607.596912] 4.13.0-rc4+ #570 Not tainted [ 607.596917] ----------------------------- [ 607.596923] net/core/dev.c:3948 suspicious rcu_dereference_check() usage! [ 607.596927] [ 607.596927] other info that might help us debug this: [ 607.596927] [ 607.596933] [ 607.596933] rcu_scheduler_active = 2, debug_locks = 1 [ 607.596938] 2 locks held by pool/14624: [ 607.596943] #0: (rcu_read_lock_bh){......}, at: [] ip_finish_output2+0x14d/0x890 [ 607.596973] #1: (rcu_read_lock_bh){......}, at: [] __dev_queue_xmit+0x14a/0xfd0 [ 607.597000] [ 607.597000] stack backtrace: [ 607.597006] CPU: 5 PID: 14624 Comm: pool Not tainted 4.13.0-rc4+ #570 [ 607.597011] Hardware name: Dell Inc. Precision Tower 5810/0HHV7N, BIOS A17 03/01/2017 [ 607.597016] Call Trace: [ 607.597027] dump_stack+0x67/0x92 [ 607.597040] lockdep_rcu_suspicious+0xdd/0x110 [ 607.597054] do_xdp_generic+0x313/0xa50 [ 607.597068] ? time_hardirqs_on+0x5b/0x150 [ 607.597076] ? mark_held_locks+0x6b/0xc0 [ 607.597088] ? netdev_pick_tx+0x150/0x150 [ 607.597117] netif_rx_internal+0x205/0x3f0 [ 607.597127] ? do_xdp_generic+0xa50/0xa50 [ 607.597144] ? lock_downgrade+0x2b0/0x2b0 [ 607.597158] ? __lock_is_held+0x93/0x100 [ 607.597187] netif_rx+0x119/0x190 [ 607.597202] loopback_xmit+0xfd/0x1b0 [ 607.597214] dev_hard_start_xmit+0x127/0x4e0 Fixes: d445516966dc ("net: xdp: support xdp generic on virtual devices") Fixes: b5cdae3291f7 ("net: Generic XDP") Signed-off-by: John Fastabend --- net/core/dev.c | 22 ++++++++++++++++------ 1 file changed, 16 insertions(+), 6 deletions(-) diff --git a/net/core/dev.c b/net/core/dev.c index 1024d37..47f4864 100644 --- a/net/core/dev.c +++ b/net/core/dev.c @@ -3981,7 +3981,13 @@ static int netif_rx_internal(struct sk_buff *skb) trace_netif_rx(skb); if (static_key_false(&generic_xdp_needed)) { - int ret = do_xdp_generic(skb); + int ret; + + preempt_disable(); + rcu_read_lock(); + ret = do_xdp_generic(skb); + rcu_read_unlock(); + preempt_enable(); /* Consider XDP consuming the packet a success from * the netdev point of view we do not want to count @@ -4499,17 +4505,21 @@ static int netif_receive_skb_internal(struct sk_buff *skb) if (skb_defer_rx_timestamp(skb)) return NET_RX_SUCCESS; - rcu_read_lock(); if (static_key_false(&generic_xdp_needed)) { - int ret = do_xdp_generic(skb); + int ret; - if (ret != XDP_PASS) { - rcu_read_unlock(); + preempt_disable(); + rcu_read_lock(); + ret = do_xdp_generic(skb); + rcu_read_unlock(); + preempt_enable(); + + if (ret != XDP_PASS) return NET_RX_DROP; - } } + rcu_read_lock(); #ifdef CONFIG_RPS if (static_key_false(&rps_needed)) { struct rps_dev_flow voidflow, *rflow = &voidflow;