From: Eric Dumazet <eric.dumazet@gmail.com>
To: David Miller <davem@davemloft.net>
Cc: netdev@vger.kernel.org
Subject: Re: [PATCH net-next-2.6] net: pskb_expand_head() optimization
Date: Tue, 07 Sep 2010 07:02:09 +0200 [thread overview]
Message-ID: <1283835729.2585.499.camel@edumazet-laptop> (raw)
In-Reply-To: <20100906.192003.232914158.davem@davemloft.net>
Le lundi 06 septembre 2010 à 19:20 -0700, David Miller a écrit :
> Eric, this goes on top of your patch and demonstrates the idea.
>
> Please review if you have a chance:
>
> diff --git a/net/core/skbuff.c b/net/core/skbuff.c
> index 2d1bc76..aeb56af 100644
> --- a/net/core/skbuff.c
> +++ b/net/core/skbuff.c
> @@ -327,6 +327,32 @@ static void skb_clone_fraglist(struct sk_buff *skb)
> skb_get(list);
> }
>
> +static struct sk_buff *skb_copy_fraglist(struct sk_buff *parent,
> + gfp_t gfp_mask)
> +{
> + struct sk_buff *first_skb = NULL;
> + struct sk_buff *prev_skb = NULL;
> + struct sk_buff *skb;
> +
> + skb_walk_frags(parent, skb) {
> + struct sk_buff *nskb = pskb_copy(skb, gfp_mask);
> +
> + if (!nskb)
> + goto fail;
> + if (!first_skb)
> + first_skb = skb;
> + else
> + prev_skb->next = skb;
> + prev_skb = skb;
> + }
> +
> + return first_skb;
> +
> +fail:
> + skb_drop_list(&first_skb);
> + return NULL;
> +}
> +
> static void skb_release_data(struct sk_buff *skb)
> {
> if (!skb->cloned ||
> @@ -812,17 +838,22 @@ int pskb_expand_head(struct sk_buff *skb, int nhead, int ntail,
> fastpath = atomic_read(&skb_shinfo(skb)->dataref) == delta;
> }
>
> - if (fastpath) {
> - kfree(skb->head);
> - } else {
> + if (!fastpath) {
> + if (skb_has_frag_list(skb)) {
> + struct sk_buff *new_list;
> +
> + new_list = skb_copy_fraglist(skb, gfp_mask);
> + if (!new_list)
> + goto free_data;
> + skb_shinfo(skb)->frag_list = new_list;
Here, skb_shinfo(skb) still points to old shinfo, you should not touch
it. An other user might need it :)
> + }
> for (i = 0; i < skb_shinfo(skb)->nr_frags; i++)
> get_page(skb_shinfo(skb)->frags[i].page);
>
> - if (skb_has_frag_list(skb))
> - skb_clone_fraglist(skb);
> -
> - skb_release_data(skb);
> }
I believe you cannot remove skb_release_data() call, we really need to
perform the atomic operation, and test the result on it, or a double
free could happen.
> +
> + kfree(skb->head);
> +
> off = (data + nhead) - skb->head;
>
> skb->head = data;
> @@ -848,6 +879,8 @@ int pskb_expand_head(struct sk_buff *skb, int nhead, int ntail,
> atomic_set(&skb_shinfo(skb)->dataref, 1);
> return 0;
>
> +free_data:
> + kfree(data);
is it a leftover ?
> nodata:
> return -ENOMEM;
> }
I understand what you want to do, but problem is we need to perform a
CAS2 operation : atomically changes two values (dataref and frag_list)
next prev parent reply other threads:[~2010-09-07 5:02 UTC|newest]
Thread overview: 33+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-09-03 3:43 [PATCH] net: Frag list lost on head expansion David Miller
2010-09-03 5:48 ` Eric Dumazet
2010-09-03 6:19 ` Eric Dumazet
2010-09-03 9:09 ` [PATCH net-next-2.6] net: pskb_expand_head() optimization Eric Dumazet
2010-09-03 13:46 ` David Miller
2010-09-07 2:20 ` David Miller
2010-09-07 5:02 ` Eric Dumazet [this message]
2010-09-07 5:05 ` David Miller
2010-09-07 9:16 ` Jarek Poplawski
2010-09-07 9:37 ` Eric Dumazet
2010-09-10 19:54 ` David Miller
2010-09-11 12:31 ` Jarek Poplawski
2010-09-12 3:30 ` David Miller
2010-09-12 10:45 ` Jarek Poplawski
2010-09-12 10:58 ` Jarek Poplawski
2010-09-12 15:58 ` David Miller
2010-09-12 16:13 ` David Miller
2010-09-12 20:57 ` Jarek Poplawski
2010-09-12 22:08 ` David Miller
2010-09-13 7:49 ` Jarek Poplawski
2010-09-12 19:55 ` Ben Pfaff
2010-09-12 20:24 ` David Miller
2010-09-12 20:45 ` Jarek Poplawski
2010-09-20 0:17 ` David Miller
2010-09-20 7:21 ` Jarek Poplawski
2010-09-20 9:02 ` Eric Dumazet
2010-09-20 9:14 ` Jarek Poplawski
2010-09-20 12:12 ` Jarek Poplawski
2010-09-20 12:40 ` Eric Dumazet
2010-09-20 16:59 ` David Miller
2010-09-07 1:25 ` David Miller
-- strict thread matches above, loose matches on Subject: below --
2010-07-22 19:12 [PATCH] Fix corruption of skb csum field in pskb_expand_head() of net/core/skbuff.c Andrea Shepard
2010-07-23 5:09 ` [PATCH net-next-2.6] net: pskb_expand_head() optimization Eric Dumazet
2010-07-25 4:06 ` David Miller
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