netdev - Re: [PATCH net 2/2] net: Call skb destructor on NAPI_GRO_FREE_STOLEN

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Date:   Wed, 18 Nov 2020 21:02:29 +0100
From:   Eric Dumazet <edumazet@...gle.com>
To:     Jakub Kicinski <kuba@...nel.org>
Cc:     Saeed Mahameed <saeedm@...dia.com>,
        netdev <netdev@...r.kernel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Maxim Mikityanskiy <maximmi@...lanox.com>,
        Tariq Toukan <tariqt@...dia.com>
Subject: Re: [PATCH net 2/2] net: Call skb destructor on NAPI_GRO_FREE_STOLEN_HEAD

On Wed, Nov 18, 2020 at 8:22 PM Jakub Kicinski <kuba@...nel.org> wrote:
>
> On Tue, 17 Nov 2020 12:33:55 -0800 Saeed Mahameed wrote:
> > From: Maxim Mikityanskiy <maximmi@...lanox.com>
> >
> > All GRO flows except one call skb->destructor, however, GRO_MERGED_FREE
> > doesn't do it in case of NAPI_GRO_FREE_STOLEN_HEAD. For better
> > consistency and to add resiliency against the drivers that may pass SKBs
> > with a destructor, this patch changes napi_skb_free_stolen_head to use
> > skb_release_head_state, which should perform all the needed cleanups,
> > including a call to the destructor. This way the code of GRO_MERGED_FREE
> > becomes similar to kfree_skb_partial.
> >
> > Fixes: e44699d2c280 ("net: handle NAPI_GRO_FREE_STOLEN_HEAD case also in napi_frags_finish()")
> > Fixes: d7e8883cfcf4 ("net: make GRO aware of skb->head_frag")
> > Signed-off-by: Maxim Mikityanskiy <maximmi@...lanox.com>
> > Reviewed-by: Tariq Toukan <tariqt@...dia.com>
> > Signed-off-by: Saeed Mahameed <saeedm@...dia.com>
>
> CC Eric for GRO expertise.

Thanks for CCing me.

Since when drivers can pass funny skbs with destructors ???

Can we please stop adding more cycles to _already_ expensive GRO ?




>
> Makes sense to me, but do you still need "net/mlx5e: Fix refcount leak
> on kTLS RX resync" even with this applied?
>
> > diff --git a/net/core/dev.c b/net/core/dev.c
> > index 82dc6b48e45f..85dcc7f19902 100644
> > --- a/net/core/dev.c
> > +++ b/net/core/dev.c
> > @@ -6048,8 +6048,7 @@ EXPORT_SYMBOL(gro_find_complete_by_type);
> >
> >  static void napi_skb_free_stolen_head(struct sk_buff *skb)
> >  {
> > -     skb_dst_drop(skb);
> > -     skb_ext_put(skb);
> > +     skb_release_head_state(skb);
> >       kmem_cache_free(skbuff_head_cache, skb);
> >  }
> >
>