netdev - Re: [PATCH v2] Revert "vrf: Remove unnecessary RCU-bh critical section"

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Message-ID: <66f5235d14130_8456129436@willemb.c.googlers.com.notmuch>
Date: Thu, 26 Sep 2024 05:03:25 -0400
From: Willem de Bruijn <willemdebruijn.kernel@...il.com>
To: greearb@...delatech.com, 
 netdev@...r.kernel.org
Cc: stable@...r.kernel.org, 
 Ben Greear <greearb@...delatech.com>
Subject: Re: [PATCH v2] Revert "vrf: Remove unnecessary RCU-bh critical
 section"

greearb@ wrote:
> From: Ben Greear <greearb@...delatech.com>
> 
> 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/
> 
> Signed-off-by: Ben Greear <greearb@...delatech.com>

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.

> ---
> 
> 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.