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

[Greg KH <gregkh@linuxfoundation.org>]

On Thu, Sep 26, 2024 at 11:19:53AM -0700, Ben Greear wrote:
> On 9/26/24 02:03, Willem de Bruijn wrote:
> > greearb@ wrote:
> > > From: Ben Greear <greearb@candelatech.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@candelatech.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.


<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>