netdev - Re: [PATCH net-next] net: switch to storing KCOV handle directly in sk

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Message-ID: <20201125124313.593fc2b5@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com>
Date:   Wed, 25 Nov 2020 12:43:13 -0800
From:   Jakub Kicinski <kuba@...nel.org>
To:     Marco Elver <elver@...gle.com>
Cc:     davem@...emloft.net, johannes@...solutions.net, a.nogikh@...il.com,
        andreyknvl@...gle.com, dvyukov@...gle.com,
        linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
        linux-wireless@...r.kernel.org, idosch@...sch.org, fw@...len.de,
        willemb@...gle.com
Subject: Re: [PATCH net-next] net: switch to storing KCOV handle directly in
 sk_buff

On Wed, 25 Nov 2020 18:34:36 +0100 Marco Elver wrote:
> diff --git a/net/core/skbuff.c b/net/core/skbuff.c
> index ffe3dcc0ebea..070b1077d976 100644
> --- a/net/core/skbuff.c
> +++ b/net/core/skbuff.c
> @@ -233,6 +233,7 @@ struct sk_buff *__alloc_skb(unsigned int size, gfp_t gfp_mask,
>  	skb->end = skb->tail + size;
>  	skb->mac_header = (typeof(skb->mac_header))~0U;
>  	skb->transport_header = (typeof(skb->transport_header))~0U;
> +	skb_set_kcov_handle(skb, kcov_common_handle());
>  
>  	/* make sure we initialize shinfo sequentially */
>  	shinfo = skb_shinfo(skb);
> @@ -249,9 +250,6 @@ struct sk_buff *__alloc_skb(unsigned int size, gfp_t gfp_mask,
>  
>  		fclones->skb2.fclone = SKB_FCLONE_CLONE;
>  	}
> -
> -	skb_set_kcov_handle(skb, kcov_common_handle());

Why the move?

>  out:
>  	return skb;
>  nodata:
> @@ -285,8 +283,6 @@ static struct sk_buff *__build_skb_around(struct sk_buff *skb,
>  	memset(shinfo, 0, offsetof(struct skb_shared_info, dataref));
>  	atomic_set(&shinfo->dataref, 1);
>  
> -	skb_set_kcov_handle(skb, kcov_common_handle());
> -
>  	return skb;
>  }

And why are we dropping this?

If this was omitted in earlier versions it's just a independent bug, 
I don't think build_skb() will call __alloc_skb(), so we need a to
set the handle here.