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

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Message-ID: <d1907a7e-1988-4570-afb5-49ee4ed4ffa2@candelatech.com>
Date: Fri, 27 Sep 2024 06:39:15 -0700
From: Ben Greear <greearb@...delatech.com>
To: Willem de Bruijn <willemdebruijn.kernel@...il.com>, netdev@...r.kernel.org
Subject: Re: [PATCH v2] Revert "vrf: Remove unnecessary RCU-bh critical
 section"

On 9/27/24 02:35, Willem de Bruijn wrote:
> Ben Greear wrote:
>> On 9/26/24 02:03, Willem de Bruijn wrote:
>>> 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.
>>
>> I was asked to add this, and also asked to CC stable.
> 
> Conflicting feedback is annoying, but I disagree with the other
> comment.
> 
> Not only does it potentially complicate backporting, it also is no
> longer a strict revert. In which case it must not be labeled as such.
> 
> Easier is to keep the revert unmodified, and add the comment to the
> commit message.
> 
> Most important is the Link to our earlier thread that explains the
> history.
> 
> If the process appears byzantine, if you prefer I can also send it.

I would appreciate it if you can send it.  As long as it functions,
I will be happy.

Thanks,
Ben

> 
> Thanks,
> 
>    Willem
> 
> 
> 

-- 
Ben Greear <greearb@...delatech.com>
Candela Technologies Inc  http://www.candelatech.com