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

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Message-ID: <66f92a1b7e5d0_13018c29434@willemb.c.googlers.com.notmuch>
Date: Sun, 29 Sep 2024 06:21:15 -0400
From: Willem de Bruijn <willemdebruijn.kernel@...il.com>
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, 
 dsahern@...nel.org, 
 Willem de Bruijn <willemb@...gle.com>
Subject: Re: [PATCH net] vrf: revert "vrf: Remove unnecessary RCU-bh critical
 section"

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>
> 
> Thanks Willem!

Thanks for testing immediately and sharing the below context, Ido!

> 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.