netdev - Re: [PATCH] net: fec: Fixed panic problem with non-tso

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Date:   Wed, 18 Jan 2017 10:18:18 -0800
From:   Pravin Shelar <pshelar@....org>
To:     Eric Dumazet <eric.dumazet@...il.com>
Cc:     "Ashizuka, Yuusuke" <ashiduka@...fujitsu.com>,
        Andy Duan <fugang.duan@....com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        Pravin B Shelar <pshelar@...ira.com>
Subject: Re: [PATCH] net: fec: Fixed panic problem with non-tso

On Tue, Jan 17, 2017 at 8:35 PM, Eric Dumazet <eric.dumazet@...il.com> wrote:
> On Tue, 2017-01-17 at 20:21 -0800, Eric Dumazet wrote:
>> On Wed, 2017-01-18 at 03:12 +0000, Ashizuka, Yuusuke wrote:
>>
>> > indeed.
>> >
>> > In the case of TSO with i.MX6 system (highmem enabled) with 2GB memory,
>> > "this_frag->page.p" did not become highmem area.
>> > (We confirmed by transferring about 100MB of files)
>> >
>> > However, in the case of non-tso on an i.MX6 system with 2GB of memory,
>> > "this_frag->page.p" may become a highmem area.
>> > (Occurred with approximately 2MB of file transfer)
>> >
>> > For non-tso only, I do not know the reason why "this_frag-> page.p"
>> > in this driver shows highmem area.
>>
>> This worries me, since this driver does not set NETIF_F_HIGHDMA in its
>> features.
>>
>> No packet should be given to this driver with a highmem fragment
>>
>> Check is done in illegal_highdma() in net/core/dev.c
>
> This used to work.
>
> I suspect commit ec5f061564238892005257c83565a0b58ec79295
> ("net: Kill link between CSUM and SG features.")
>
> added this bug.
>
> Can you try this hot fix :
>
> diff --git a/net/core/dev.c b/net/core/dev.c
> index ad5959e561166f445bdd9d7260652a338f74cfea..073b832b945257dba9ed47f4bf875605225effc9 100644
> --- a/net/core/dev.c
> +++ b/net/core/dev.c
> @@ -2773,9 +2773,9 @@ static netdev_features_t harmonize_features(struct sk_buff *skb,
>         if (skb->ip_summed != CHECKSUM_NONE &&
>             !can_checksum_protocol(features, type)) {
>                 features &= ~(NETIF_F_CSUM_MASK | NETIF_F_GSO_MASK);
> -       } else if (illegal_highdma(skb->dev, skb)) {
> -               features &= ~NETIF_F_SG;
>         }
> +       if (illegal_highdma(skb->dev, skb))
> +               features &= ~NETIF_F_SG;
>
>         return features;
>  }

Right, this high mem check should be decoupled from csum check.

Thanks,
Pravin.