Message ID | 150490443011.11590.2847947557652786219.stgit@john-XPS-13-9360 |
---|---|
State | Accepted, archived |
Delegated to: | David Miller |
Headers | show |
Series | Fixes for XDP/BPF | expand |
On 9/8/17 2:00 PM, John Fastabend wrote: > 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: [<ffffffff95445ffd>] ip_finish_output2+0x14d/0x890 > [ 607.596973] #1: (rcu_read_lock_bh){......}, at: [<ffffffff953c8e3a>] __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") > Acked-by: Daniel Borkmann <daniel@iogearbox.net> > Signed-off-by: John Fastabend <john.fastabend@gmail.com> argh, so it's due to virtual devices and loopback. Not pretty, but have to agree I don't see another way of fixing it. Acked-by: Alexei Starovoitov <ast@kernel.org>
diff --git a/net/core/dev.c b/net/core/dev.c index 6f845e4..fb766d9 100644 --- a/net/core/dev.c +++ b/net/core/dev.c @@ -3981,8 +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(rcu_dereference(skb->dev->xdp_prog), - skb); + int ret; + + preempt_disable(); + rcu_read_lock(); + ret = do_xdp_generic(rcu_dereference(skb->dev->xdp_prog), 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 @@ -4500,18 +4505,20 @@ 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(rcu_dereference(skb->dev->xdp_prog), - skb); + int ret; - if (ret != XDP_PASS) { - rcu_read_unlock(); + preempt_disable(); + rcu_read_lock(); + ret = do_xdp_generic(rcu_dereference(skb->dev->xdp_prog), 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;