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")
Signed-off-by: John Fastabend <john.fastab...@gmail.com>
---
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;
