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

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Message-ID: <6676d990-e7b4-4b90-8d2b-a96107e38b63@kernel.org>
Date: Sun, 29 Sep 2024 10:32:28 -0600
From: David Ahern <dsahern@...nel.org>
To: Ido Schimmel <idosch@...dia.com>,
 Willem de Bruijn <willemdebruijn.kernel@...il.com>
Cc: netdev@...r.kernel.org, davem@...emloft.net, kuba@...nel.org,
 edumazet@...gle.com, pabeni@...hat.com, stable@...r.kernel.org,
 greearb@...delatech.com, fw@...len.de, Willem de Bruijn <willemb@...gle.com>
Subject: Re: [PATCH net] vrf: revert "vrf: Remove unnecessary RCU-bh critical
 section"

On 9/29/24 3:11 AM, Ido Schimmel wrote:
> On Sun, Sep 29, 2024 at 02:18:20AM -0400, Willem de Bruijn wrote:
>> 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:
> 
> [...]
> 
>>
>> 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
> 
> Reviewed-by: Ido Schimmel <idosch@...dia.com>
> Tested-by: Ido Schimmel <idosch@...dia.com>

Reviewed-by: David Ahern <dsahern@...nel.org>


> 
> Thanks Willem!
> 
> The reason my script from 504fc6f4f7f6 did not trigger the problem is
> that it was pinging the address inside the VRF, so vrf_finish_direct()
> was only called from the Rx path.
> 
> If you ping the address outside of the VRF:
> 
> ping -I vrf1 -i 0.1 -c 10 -q 192.0.2.1
> 
> Then vrf_finish_direct() is called from process context and the lockdep
> warning is triggered. Tested that it does not trigger after applying the
> revert.

That case should be covered by the fcnal-test suite which does all
combinations of addresses.