netdev - RE: [PATCH net-next v3 00/14] Add functional support for Gigabit Ethernet driver

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Date:   Tue, 12 Oct 2021 18:53:50 +0000
From:   Biju Das <biju.das.jz@...renesas.com>
To:     Jakub Kicinski <kuba@...nel.org>
CC:     "David S. Miller" <davem@...emloft.net>,
        Sergey Shtylyov <s.shtylyov@....ru>,
        Sergei Shtylyov <sergei.shtylyov@...il.com>,
        Prabhakar Mahadev Lad <prabhakar.mahadev-lad.rj@...renesas.com>,
        Andrew Lunn <andrew@...n.ch>,
        Geert Uytterhoeven <geert+renesas@...der.be>,
        Adam Ford <aford173@...il.com>,
        Yoshihiro Shimoda <yoshihiro.shimoda.uh@...esas.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-renesas-soc@...r.kernel.org>, Chris Paterson
        <Chris.Paterson2@...esas.com>, Biju Das <biju.das@...renesas.com" 
        <linux-renesas-soc@...r.kernel.org>
Subject: RE: [PATCH net-next v3 00/14] Add functional support for Gigabit
 Ethernet driver


Hi Jakub Kicinski,

Thanks for the feedback.

> Subject: Re: [PATCH net-next v3 00/14] Add functional support for Gigabit
> Ethernet driver
> 
> On Tue, 12 Oct 2021 18:28:07 +0000 Biju Das wrote:
> > > On Tue, 12 Oct 2021 17:35:59 +0100 Biju Das wrote:
> > > > set_feature patch will send as separate RFC patch along with
> > > > rx_checksum patch, as it needs further discussion related to HW
> > > checksum.
> > >
> > > Is this part relating to the crash you observed because of TCP csum
> > > offload?
> >
> > Yes, you are correct. Sergey, suggested use R-Car RX-HW checksum with
> > RCSC/RCPT and But the TOE gives either 0x0 or 0xffff as csum output
> > and feeding this value to skb->csum lead to kernel crash.
> 
> That's quite concerning. Do you have any of the
> 
> /proc/sys/kernel/panic_on_io_nmi
> /proc/sys/kernel/panic_on_oops
> /proc/sys/kernel/panic_on_rcu_stall
> /proc/sys/kernel/panic_on_unrecovered_nmi
> /proc/sys/kernel/panic_on_warn
> 
> knobs set? I'm guessing we hit do_netdev_rx_csum_fault() when the checksum
> is incorrect, but I'm surprised that causes a panic.
> 

I tested this last week, if I remember correctly It was not panic, rather do_netdev_rx_csum_fault. I will recheck and will send you the stack trace next time. 

> 
> BTW are you seeing 0 / ffff with good or bad checksums? If the device does
> a checksum over the IP pseudo-header + TCP only - 0 and ffff would be
> correct for a packet with has a valid checksum. But you can't set it to
> skb->csum and use CSUM_COMPLETE, you'd need to do something like:
> 
> if (dev_csum == 0 || dev_csum == 0xffff)
> 	skb->ip_summed = CHECKSUM_UNNECESSARY;

Yes, it computes IPv4 header checksum and TCP/UDP/ICMP checksum.

It will set to 0x0 for both csums, if there is no error.

For IPV6, ipv4 header checksum is always set to 0xffff and 0 for TCP/UDP/ICMP checksum.

Ok I will use this logic on next RFC.

Regards,
Biju