netdev - Re: [PATCH net 1/4] bonding: fix send_peer

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Message-ID: <ZEIGCaLWKIY3lDBo@Laptop-X1>
Date:   Fri, 21 Apr 2023 11:42:01 +0800
From:   Hangbin Liu <liuhangbin@...il.com>
To:     Jakub Kicinski <kuba@...nel.org>
Cc:     Jay Vosburgh <jay.vosburgh@...onical.com>,
        kernel test robot <lkp@...el.com>, netdev@...r.kernel.org,
        oe-kbuild-all@...ts.linux.dev,
        "David S . Miller" <davem@...emloft.net>,
        Paolo Abeni <pabeni@...hat.com>,
        Eric Dumazet <edumazet@...gle.com>,
        Liang Li <liali@...hat.com>, Vincent Bernat <vincent@...nat.ch>
Subject: Re: [PATCH net 1/4] bonding: fix send_peer_notif overflow

On Thu, Apr 20, 2023 at 04:21:39PM -0700, Jakub Kicinski wrote:
> On Thu, 20 Apr 2023 08:59:40 -0700 Jay Vosburgh wrote:
> > >All errors (new ones prefixed by >>, old ones prefixed by <<):
> > >  
> > >>> ERROR: modpost: "__umoddi3" [drivers/net/bonding/bonding.ko] undefined!  
> > 
> > 	I assume this is related to send_peer_notif now being u64 in the
> > modulus at:
> > 
> > static bool bond_should_notify_peers(struct bonding *bond)
> > {
> > [...]
> >         if (!slave || !bond->send_peer_notif ||
> >             bond->send_peer_notif %
> >             max(1, bond->params.peer_notif_delay) != 0 ||
> > 
> > 	but I'm unsure if this is a real coding error, or some issue
> > with the parisc arch specifically?
> 
> Coding error, I think. 
> An appropriate helper from linux/math64.h should be used.

It looks define send_peer_notif to u64 is a bit too large, which introduce
complex conversion for 32bit arch.

For the remainder operation,
bond->send_peer_notif % max(1, bond->params.peer_notif_delay). u32 % u32 look OK.

But for multiplication operation,
bond->send_peer_notif = bond->params.num_peer_notif * max(1, bond->params.peer_notif_delay);
It's u8 * u32. How about let's limit the peer_notif_delay to less than max(u32 / u8),
then we can just use u32 for send_peer_notif. Is there any realistic meaning
to set peer_notif_delay to max(u32)? I don't think so.

Jay, what do you think?

Thanks
Hangbin