On Thu, Sep 26, 2024 at 11:19:53AM -0700, Ben Greear wrote:

On 9/26/24 02:03, Willem de Bruijn wrote:

quoted

greearb@ wrote:

quoted

From: Ben Greear <redacted>

This reverts commit 504fc6f4f7f681d2a03aa5f68aad549d90eab853.

dev_queue_xmit_nit needs to run with bh locking, otherwise
it conflicts with packets coming in from a nic in softirq
context and packets being transmitted from user context.

================================
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
   napi_complete_done+0x1c0/0x7c0
   igb_poll+0x1dbb/0x57e0 [igb]
   __napi_poll.constprop.0+0x99/0x430
   net_rx_action+0x8e7/0xe10
   handle_softirqs+0x1b7/0x800
   __irq_exit_rcu+0x91/0xc0
   irq_exit_rcu+0x5/0x10
   [snip]

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
[snip]

Fixes: 504fc6f4f7f6 ("vrf: Remove unnecessary RCU-bh critical section")
Link: https://lore.kernel.org/netdev/05765015-f727-2f30-58da-2ad6fa7ea99f@candelatech.com/T/ (local)

Signed-off-by: Ben Greear <redacted>

Please Cc: all previous reviewers and folks who participated in the
discussion. I entirely missed this. No need to add as Cc tags, just
--cc in git send-email will do.

quoted

---

v2:  Edit patch description.

  drivers/net/vrf.c | 2 ++
  net/core/dev.c    | 1 +
  2 files changed, 3 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);
  	}

diff --git a/net/core/dev.c b/net/core/dev.c
index cd479f5f22f6..566e69a38eed 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c

@@ -2285,6 +2285,7 @@ EXPORT_SYMBOL_GPL(dev_nit_active);
  /*
   *	Support routine. Sends outgoing frames to any network
   *	taps currently in use.
+ *	BH must be disabled before calling this.

Unnecessary. Especially patches for stable should be minimal to
reduce the chance of conflicts.

I was asked to add this, and also asked to CC stable.

<formletter>

This is not the correct way to submit patches for inclusion in the
stable kernel tree.  Please read:
    https://www.kernel.org/doc/html/latest/process/stable-kernel-rules.html
for how to do this properly.

</formletter>