netdev - Re: [PATCH] skbuff: skb_segment, Update nfrags after calling zero copy functions

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Message-ID: <CANn89iKHTaiqyBohSd3sRJJwG1CUD2M_vy6gwLjW=U4VS3EJtQ@mail.gmail.com>
Date: Wed, 30 Aug 2023 05:44:15 +0200
From: Eric Dumazet <edumazet@...gle.com>
To: Mohamed Khalfella <mkhalfella@...estorage.com>
Cc: willemjdebruijn <willemdebruijn.kernel@...il.com>, 
	"David S. Miller" <davem@...emloft.net>, Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, 
	Willem de Bruijn <willemb@...gle.com>, Alexander Duyck <alexanderduyck@...com>, 
	David Howells <dhowells@...hat.com>, Jesper Dangaard Brouer <brouer@...hat.com>, 
	Kees Cook <keescook@...omium.org>, 
	"open list:NETWORKING [GENERAL]" <netdev@...r.kernel.org>, open list <linux-kernel@...r.kernel.org>, 
	"open list:BPF [MISC]" <bpf@...r.kernel.org>
Subject: Re: [PATCH] skbuff: skb_segment, Update nfrags after calling zero
 copy functions

On Wed, Aug 30, 2023 at 12:24 AM Mohamed Khalfella
<mkhalfella@...estorage.com> wrote:
>
> On 2023-08-29 12:09:15 +0200, Eric Dumazet wrote:
> > Another way to test this path for certain (without tcpdump having to race)
> > is to add a temporary/debug patch like this one:
> >
> > diff --git a/net/core/skbuff.c b/net/core/skbuff.c
> > index a298992060e6efdecb87c7ffc8290eafe330583f..20cc42be5e81cdca567515f2a886af4ada0fbe0a
> > 100644
> > --- a/net/core/skbuff.c
> > +++ b/net/core/skbuff.c
> > @@ -1749,7 +1749,8 @@ int skb_copy_ubufs(struct sk_buff *skb, gfp_t gfp_mask)
> >         int i, order, psize, new_frags;
> >         u32 d_off;
> >
> > -       if (skb_shared(skb) || skb_unclone(skb, gfp_mask))
> > +       if (skb_shared(skb) ||
> > +           pskb_expand_head(skb, 0, 0, gfp_mask))
> >                 return -EINVAL;
> >
> >         if (!num_frags)
> >
> > Note that this might catch other bugs :/
>
> I was not able to make it allocate a new frags by running tcpdump while
> reproing the problem. However, I was able to do it with your patch.

I am glad this worked, and looking forward to a v2 of your patch, thanks !