netdev - Re: [PATCH net] sctp: increase sk_wmem_alloc when head->truesize is increased

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Date:   Mon, 26 Nov 2018 21:49:34 +0900
From:   Xin Long <lucien.xin@...il.com>
To:     Neil Horman <nhorman@...driver.com>
Cc:     network dev <netdev@...r.kernel.org>, linux-sctp@...r.kernel.org,
        davem <davem@...emloft.net>,
        Marcelo Ricardo Leitner <marcelo.leitner@...il.com>
Subject: Re: [PATCH net] sctp: increase sk_wmem_alloc when head->truesize is increased

On Mon, Nov 26, 2018 at 9:27 PM Neil Horman <nhorman@...driver.com> wrote:
>
> On Mon, Nov 26, 2018 at 02:52:44PM +0800, Xin Long wrote:
> > I changed to count sk_wmem_alloc by skb truesize instead of 1 to
> > fix the sk_wmem_alloc leak caused by later truesize's change in
> > xfrm in Commit 02968ccf0125 ("sctp: count sk_wmem_alloc by skb
> > truesize in sctp_packet_transmit").
> >
> > But I should have also increased sk_wmem_alloc when head->truesize
> > is increased in sctp_packet_gso_append() as xfrm does. Otherwise,
> > sctp gso packet will cause sk_wmem_alloc underflow.
> >
> > Fixes: 02968ccf0125 ("sctp: count sk_wmem_alloc by skb truesize in sctp_packet_transmit")
> > Signed-off-by: Xin Long <lucien.xin@...il.com>
> > ---
> >  net/sctp/output.c | 1 +
> >  1 file changed, 1 insertion(+)
> >
> > diff --git a/net/sctp/output.c b/net/sctp/output.c
> > index b0e74a3..025f48e 100644
> > --- a/net/sctp/output.c
> > +++ b/net/sctp/output.c
> > @@ -410,6 +410,7 @@ static void sctp_packet_gso_append(struct sk_buff *head, struct sk_buff *skb)
> >       head->truesize += skb->truesize;
> >       head->data_len += skb->len;
> >       head->len += skb->len;
> > +     refcount_add(skb->truesize, &head->sk->sk_wmem_alloc);
> >
> >       __skb_header_release(skb);
> >  }
> This looks to me like you are now double counting every packet that passes
> through sctp_packet_transmit, once in skb_set_owner_w and again in
> sctp_packet_pack=>sctp_packet_gso_append
For gso packet, the skb(head) in sctp_packet_transmit/skb_set_owner_w
is the head_skb, the skbs here are the fragments.

For non-gso packet, it will never come here.

>
> Neil
>
> > --
> > 2.1.0
> >
> >