netdev - [PATCH net] vrf: revert "vrf: Remove unnecessary RCU-bh critical section"

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Message-ID: <20240929061839.1175300-1-willemdebruijn.kernel@gmail.com>
Date: Sun, 29 Sep 2024 02:18:20 -0400
From: Willem de Bruijn <willemdebruijn.kernel@...il.com>
To: netdev@...r.kernel.org
Cc: davem@...emloft.net,
	kuba@...nel.org,
	edumazet@...gle.com,
	pabeni@...hat.com,
	stable@...r.kernel.org,
	greearb@...delatech.com,
	fw@...len.de,
	dsahern@...nel.org,
	idosch@...dia.com,
	Willem de Bruijn <willemb@...gle.com>
Subject: [PATCH net] vrf: revert "vrf: Remove unnecessary RCU-bh critical section"

From: Willem de Bruijn <willemb@...gle.com>

This reverts commit 504fc6f4f7f681d2a03aa5f68aad549d90eab853.

dev_queue_xmit_nit is expected to be called with BH disabled.
__dev_queue_xmit has the following:

        /* Disable soft irqs for various locks below. Also
         * stops preemption for RCU.
         */
        rcu_read_lock_bh();

VRF must follow this invariant. The referenced commit removed this
protection. Which triggered a lockdep warning:

	================================
	WARNING: inconsistent lock state
	6.11.0 #1 Tainted: G        W
	--------------------------------
	inconsistent {IN-SOFTIRQ-W} -> {SOFTIRQ-ON-W} usage.
	btserver/134819 [HC0[0]:SC0[0]:HE1:SE1] takes:
	ffff8882da30c118 (rlock-AF_PACKET){+.?.}-{2:2}, at: tpacket_rcv+0x863/0x3b30
	{IN-SOFTIRQ-W} state was registered at:
	  lock_acquire+0x19a/0x4f0
	  _raw_spin_lock+0x27/0x40
	  packet_rcv+0xa33/0x1320
	  __netif_receive_skb_core.constprop.0+0xcb0/0x3a90
	  __netif_receive_skb_list_core+0x2c9/0x890
	  netif_receive_skb_list_internal+0x610/0xcc0
          [...]

	other info that might help us debug this:
	 Possible unsafe locking scenario:

	       CPU0
	       ----
	  lock(rlock-AF_PACKET);
	  <Interrupt>
	    lock(rlock-AF_PACKET);

	 *** DEADLOCK ***

	Call Trace:
	 <TASK>
	 dump_stack_lvl+0x73/0xa0
	 mark_lock+0x102e/0x16b0
	 __lock_acquire+0x9ae/0x6170
	 lock_acquire+0x19a/0x4f0
	 _raw_spin_lock+0x27/0x40
	 tpacket_rcv+0x863/0x3b30
	 dev_queue_xmit_nit+0x709/0xa40
	 vrf_finish_direct+0x26e/0x340 [vrf]
	 vrf_l3_out+0x5f4/0xe80 [vrf]
	 __ip_local_out+0x51e/0x7a0
          [...]

Fixes: 504fc6f4f7f6 ("vrf: Remove unnecessary RCU-bh critical section")
Link: https://lore.kernel.org/netdev/20240925185216.1990381-1-greearb@candelatech.com/
Reported-by: Ben Greear <greearb@...delatech.com>
Signed-off-by: Willem de Bruijn <willemb@...gle.com>
Cc: stable@...r.kernel.org
---
 drivers/net/vrf.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/net/vrf.c b/drivers/net/vrf.c
index 4d8ccaf9a2b4..4087f72f0d2b 100644
--- a/drivers/net/vrf.c
+++ b/drivers/net/vrf.c
@@ -608,7 +608,9 @@ static void vrf_finish_direct(struct sk_buff *skb)
 		eth_zero_addr(eth->h_dest);
 		eth->h_proto = skb->protocol;
 
+		rcu_read_lock_bh();
 		dev_queue_xmit_nit(skb, vrf_dev);
+		rcu_read_unlock_bh();
 
 		skb_pull(skb, ETH_HLEN);
 	}
-- 
2.46.1.824.gd892dcdcdd-goog