From mboxrd@z Thu Jan  1 00:00:00 1970
From: Jarek Poplawski <jarkao2-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
Subject: Re: [Bug #16626] Machine hangs with EIP at skb_copy_and_csum_dev
Date: Wed, 1 Sep 2010 17:05:04 +0200
Message-ID: <20100901150504.GA3091@del.dom.local>
References: <4LwrqITm-eJ.A.r8G.eFueMB@chimera>
 <4AUWBNzTkbD.A.ey.cGueMB@chimera>
 <courier.4C7C99F2.00001F74@fs.ru.acad.bg>
 <20100831192659.GA3093@del.dom.local>
 <1283338251.2556.124.camel@edumazet-laptop>
 <20100901112026.GA9468@ff.dom.local>
 <1283349461.2556.333.camel@edumazet-laptop>
Mime-Version: 1.0
Content-Transfer-Encoding: QUOTED-PRINTABLE
Return-path: <kernel-testers-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed;
        d=gmail.com; s=gamma;
        h=domainkey-signature:received:received:date:from:to:cc:subject
         :message-id:references:mime-version:content-type:content-disposition
         :content-transfer-encoding:in-reply-to:user-agent;
        bh=1dDP2V10iHNAI5BS77h+uZPGmV186aRroxNUXDK6fTE=;
        b=r13GY5Nqyr71fQE364xJTWOEMpENS5eWJcxUo25UYhSy62PoLKAiOTzUzUILZQDxyv
         M4hXa/etj4Ckz0uoVyaFmiIomyCUgv+JgXvfr5Nv/9NO6OXHswKeznZRv6rDKfDcVM4G
         +ul5sqw7SC5cIH1AVWteNBuVyGMW43rRqDLD4=
Content-Disposition: inline
In-Reply-To: <1283349461.2556.333.camel@edumazet-laptop>
Sender: kernel-testers-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org
List-ID: <kernel-testers.vger.kernel.org>
Content-Type: text/plain; charset="iso-8859-1"
To: Eric Dumazet <eric.dumazet-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
Cc: Plamen Petrov <pvp-lsts-s6OjJRe3oxUfI6EYonfoRA@public.gmane.org>, Herbert Xu <herbert-lOAM2aK0SrRLBo1qDEOMRrpzq4S04n8Q@public.gmane.org>, "Rafael J. Wysocki" <rjw-KKrjLPT3xs0@public.gmane.org>, Kernel Testers List <kernel-testers-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>, Maciej Rutecki <maciej.rutecki-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>, "David S. Miller" <davem-fT/PcQaiUtIeIZ0/mPfg9Q@public.gmane.org>, Linux Kernel Mailing List <linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>, netdev-u79uwXL29TY76Z2rM5mHXA@public.gmane.org

On Wed, Sep 01, 2010 at 03:57:41PM +0200, Eric Dumazet wrote:
> Le mercredi 01 septembre 2010 ?? 11:20 +0000, Jarek Poplawski a =E9cr=
it :
> > On Wed, Sep 01, 2010 at 12:50:51PM +0200, Eric Dumazet wrote:
> > > Plamen, could you test following patch ?
> > >=20
> > > I reproduced problem on a dev machine and following patch cured i=
t.
> > >=20
> > > Thanks
> > >=20
> > > [PATCH] gro: fix different skb headrooms
> > >=20
> > > packets entering GRO might have different headrooms, even for a g=
iven
> > > flow (because of implementation details in drivers, like copybrea=
k).
> > > We cant force drivers to deliver packets with a fixed headroom.
> > >=20
> > > 1) fix skb_segment()
> > >=20
> > > skb_segment() makes the false assumption headrooms of fragments a=
re same
> > > than the head. When CHECKSUM_PARTIAL is used, this can give csum_=
start
> > > errors, and crash later in skb_copy_and_csum_dev()
> >=20
> > Eric, probably I missed something, but since the same test as in
> > skb_copy_and_csum_dev() gave different result a bit earlier on exac=
tly
> > the same skb, I've suspected some sharing (or use after free)
> > problems, so I'm not sure your current diagnose can explain this.
> > (Unless this old test was dismissed later.)
>=20
> Oh, this is because your patch had an error for the gso part that rea=
d :
>=20
> -               rc =3D ops->ndo_start_xmit(nskb, dev);
> +               if (skb_csum_start_bug(skb, 50)) {
> +                       kfree_skb(skb);
> +                       rc =3D NETDEV_TX_OK;
> +               } else
> +                       rc =3D ops->ndo_start_xmit(nskb, dev);
> +
>                 if (unlikely(rc !=3D NETDEV_TX_OK)) {
>                         if (rc & ~NETDEV_TX_MASK)
>                                 goto out_kfree_gso_skb;
>=20
> You called skb_csum_start_bug(skb, 50) instead of
> skb_csum_start_bug(nskb, 50)
>=20
> Hope this clarify a bit ;)

All clear! Sorry for the false alarm!

Thanks,
Jarek P.