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From: Vasily Averin <vvs@virtuozzo.com>
To: Christoph Paasch <christoph.paasch@gmail.com>
Cc: "David S. Miller" <davem@davemloft.net>,
	Hideaki YOSHIFUJI <yoshfuji@linux-ipv6.org>,
	David Ahern <dsahern@kernel.org>,
	Jakub Kicinski <kuba@kernel.org>,
	Eric Dumazet <eric.dumazet@gmail.com>,
	netdev <netdev@vger.kernel.org>,
	LKML <linux-kernel@vger.kernel.org>,
	kernel@openvz.org, Julian Wiedmann <jwi@linux.ibm.com>
Subject: Re: [PATCH NET v4 3/7] ipv6: use skb_expand_head in ip6_xmit
Date: Mon, 23 Aug 2021 08:44:29 +0300	[thread overview]
Message-ID: <7d71f2cc-3fff-beff-b82b-d0a81fb60429@virtuozzo.com> (raw)
In-Reply-To: <CALMXkpYeR+DegQJ7Eec2cx=z8i+Z8Y-Aygftjg08Y2+bQXJZ7Q@mail.gmail.com>

On 8/22/21 8:13 PM, Christoph Paasch wrote:
> On Sun, Aug 22, 2021 at 10:04 AM Christoph Paasch
> <christoph.paasch@gmail.com> wrote:
>>
>> Hello Vasily,
>>
>> On Fri, Aug 20, 2021 at 11:21 PM Vasily Averin <vvs@virtuozzo.com> wrote:
>>>
>>> On 8/21/21 1:44 AM, Christoph Paasch wrote:
>>>> (resend without html - thanks gmail web-interface...)
>>>> On Fri, Aug 20, 2021 at 3:41 PM Christoph Paasch
>>>>> AFAICS, this is because pskb_expand_head (called from
>>>>> skb_expand_head) is not adjusting skb->truesize when skb->sk is set
>>>>> (which I guess is the case in this particular scenario). I'm not
>>>>> sure what the proper fix would be though...
>>>
>>> Could you please elaborate?
>>> it seems to me skb_realloc_headroom used before my patch called pskb_expand_head() too
>>> and did not adjusted skb->truesize too. Am I missed something perhaps?
>>>
>>> The only difference in my patch is that skb_clone can be not called,
>>> though I do not understand how this can affect skb->truesize.
>>
>> I *believe* that the difference is that after skb_clone() skb->sk is
>> NULL and thus truesize will be adjusted.
>>
>> I will try to confirm that with some more debugging.
> 
> Yes indeed.
> 
> Before your patch:
> [   19.154039] ip6_xmit before realloc truesize 4864 sk? 000000002ccd6868
> [   19.155230] ip6_xmit after realloc truesize 5376 sk? 0000000000000000
> 
> skb->sk is not set and thus truesize will be adjusted.

This looks strange for me. skb should not lost sk reference.

Could you please clarify where exactly you cheked it?
sk on newly allocated skb is set on line 291

net/ipv6/ip6_output.c::ip6_xmit()
 282         if (unlikely(skb_headroom(skb) < head_room)) {
 283                 struct sk_buff *skb2 = skb_realloc_headroom(skb, head_room);
 284                 if (!skb2) {
 285                         IP6_INC_STATS(net, ip6_dst_idev(skb_dst(skb)),
 286                                       IPSTATS_MIB_OUTDISCARDS);
 287                         kfree_skb(skb);
 288                         return -ENOBUFS;
 289                 }
 290                 if (skb->sk)
 291                         skb_set_owner_w(skb2, skb->sk); <<<<< here
 292                 consume_skb(skb);
 293                 skb = skb2;
 294         }

> With your change:
> [   15.092933] ip6_xmit before realloc truesize 4864 sk? 00000000072930fd
> [   15.094131] ip6_xmit after realloc truesize 4864 sk? 00000000072930fd
> 
> skb->sk is set and thus truesize is not adjusted.

In this case skb_set_owner_w() is called inside skb_expand_head()

net/ipv6/ip6_output.c::ip6_xmit()
 265         if (unlikely(head_room > skb_headroom(skb))) {
 266                 skb = skb_expand_head(skb, head_room);
 267                 if (!skb) {
 268                         IP6_INC_STATS(net, idev, IPSTATS_MIB_OUTDISCARDS);
 269                         return -ENOBUFS;
 270                 }
 271         }

net/core/skbuff.c::skb_expand_head()
1813         if (skb_shared(skb)) {
1814                 struct sk_buff *nskb = skb_clone(skb, GFP_ATOMIC);
1815 
1816                 if (likely(nskb)) {
1817                         if (skb->sk)
1818                                 skb_set_owner_w(nskb, skb->sk);  <<<< here
1819                         consume_skb(skb);
1820                 } else {
1821                         kfree_skb(skb);
1822                 }
1823                 skb = nskb;
1824         }

So I do not understand how this can happen.
With my patch: 
a) if skb is not shared -- it should keep original skb->sk
b) if skb is shared -- new skb should set sk if it was set on original skb.

Your results can be explained if you looked and skb->sk and truesize right after skb_realloc_headroom() call
but  before following skb_set_owner_w(). Could you please check it?

Thank you,
	Vasily Averin

  reply	other threads:[~2021-08-23  5:44 UTC|newest]

Thread overview: 106+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <cover.1625665132.git.vvs@virtuozzo.com>
2021-07-07 14:04 ` [PATCH IPV6 1/1] ipv6: allocate enough headroom in ip6_finish_output2() Vasily Averin
2021-07-07 14:45   ` David Ahern
2021-07-07 16:42     ` Jakub Kicinski
2021-07-07 17:41       ` Eric Dumazet
2021-07-07 17:53         ` Vasily Averin
2021-07-07 18:30         ` Jakub Kicinski
2021-07-07 18:50           ` Eric Dumazet
2021-07-09  9:04         ` [PATCH IPV6 v2 0/4] " Vasily Averin
2021-07-12  6:44           ` [PATCH IPV6 v3 0/1] " Vasily Averin
     [not found]           ` <cover.1626069562.git.vvs@virtuozzo.com>
2021-07-12  6:45             ` [PATCH IPV6 v3 1/1] " Vasily Averin
2021-07-12 18:30               ` patchwork-bot+netdevbpf
2021-07-13  7:46               ` Vasily Averin
2021-07-13 12:01                 ` [PATCH NET v4 0/1] " Vasily Averin
     [not found]                 ` <cover.1626177047.git.vvs@virtuozzo.com>
2021-07-13 12:01                   ` [PATCH NET v4 1/1] " Vasily Averin
2021-07-18 10:44                     ` Vasily Averin
2021-07-18 15:22                       ` David Ahern
2021-07-18 17:04                       ` David Miller
2021-07-19  7:55                         ` [PATCH NET] ipv6: ip6_finish_output2: set sk into newly allocated nskb Vasily Averin
2021-07-20 10:10                           ` patchwork-bot+netdevbpf
2021-07-13 12:31                 ` [PATCH IPV6 v3 1/1] ipv6: allocate enough headroom in ip6_finish_output2() Vasily Averin
2021-07-12 13:26           ` [PATCH NET 0/7] skbuff: introduce pskb_realloc_headroom() Vasily Averin
     [not found]           ` <cover.1626093470.git.vvs@virtuozzo.com>
2021-07-12 13:26             ` [PATCH NET 1/7] " Vasily Averin
2021-07-12 17:53               ` Jakub Kicinski
2021-07-12 18:45                 ` Vasily Averin
2021-07-13 20:57                   ` [PATCH NET v2 0/7] skbuff: introduce skb_expand_head() Vasily Averin
2021-08-02  8:52                     ` [PATCH NET v3 " Vasily Averin
     [not found]                     ` <cover.1627891754.git.vvs@virtuozzo.com>
2021-08-02  8:52                       ` [PATCH NET v3 1/7] " Vasily Averin
2021-08-02  8:52                       ` [PATCH NET v3 2/7] ipv6: use skb_expand_head in ip6_finish_output2 Vasily Averin
2021-08-02  8:52                       ` [PATCH NET v3 3/7] ipv6: use skb_expand_head in ip6_xmit Vasily Averin
2021-08-02  8:52                       ` [PATCH NET v3 4/7] ipv4: use skb_expand_head in ip_finish_output2 Vasily Averin
2021-08-02  8:52                       ` [PATCH NET v3 5/7] vrf: use skb_expand_head in vrf_finish_output Vasily Averin
2021-08-05 11:55                         ` Julian Wiedmann
2021-08-05 12:55                           ` Vasily Averin
2021-08-06  7:49                           ` [PATCH NET v4 0/7] skbuff: introduce skb_expand_head() Vasily Averin
2021-08-06 10:14                             ` David Miller
2021-08-06 12:53                               ` [PATCH NET] vrf: fix null pointer dereference in vrf_finish_output() Vasily Averin
2021-08-06 22:42                                 ` Jakub Kicinski
2021-08-07  6:41                                   ` Vasily Averin
     [not found]                           ` <cover.1628235065.git.vvs@virtuozzo.com>
2021-08-06  7:49                             ` [PATCH NET v4 1/7] skbuff: introduce skb_expand_head() Vasily Averin
2021-08-06  7:50                             ` [PATCH NET v4 2/7] ipv6: use skb_expand_head in ip6_finish_output2 Vasily Averin
2021-08-06  7:50                             ` [PATCH NET v4 3/7] ipv6: use skb_expand_head in ip6_xmit Vasily Averin
     [not found]                               ` <CALMXkpaay1y=0tkbnskr4gf-HTMjJJsVryh4Prnej_ws-hJvBg@mail.gmail.com>
2021-08-20 22:44                                 ` Christoph Paasch
2021-08-21  6:21                                   ` Vasily Averin
2021-08-22 17:04                                     ` Christoph Paasch
2021-08-22 17:13                                       ` Christoph Paasch
2021-08-23  5:44                                         ` Vasily Averin [this message]
2021-08-23  5:59                                           ` Vasily Averin
2021-08-23  7:56                                             ` [PATCH NET-NEXT] ipv6: skb_expand_head() adjust skb->truesize incorrectly Vasily Averin
2021-08-23 17:25                                               ` Christoph Paasch
2021-08-23 21:45                                                 ` Eric Dumazet
2021-08-23 21:51                                                   ` Eric Dumazet
2021-08-23 22:23                                                     ` Eric Dumazet
2021-08-24  8:50                                                       ` Vasily Averin
2021-08-24 17:21                                                         ` Vasily Averin
2021-08-25 17:49                                                           ` Christoph Paasch
2021-08-29 12:59                                                             ` [PATCH v2] " Vasily Averin
2021-08-30  5:52                                                               ` [PATCH net-next " Vasily Averin
2021-08-30 16:01                                                               ` [PATCH " Eric Dumazet
2021-08-30 18:09                                                                 ` Vasily Averin
2021-08-30 18:37                                                                   ` Vasily Averin
2021-08-30 19:58                                                                   ` Eric Dumazet
2021-08-31 14:34                                                                     ` [PATCH net-next v3 RFC] " Vasily Averin
2021-08-31 19:38                                                                       ` Eric Dumazet
2021-09-01  6:20                                                                         ` Vasily Averin
2021-09-01  8:11                                                                           ` [PATCH net-next v4] " Vasily Averin
2021-09-01 16:58                                                                             ` Christoph Paasch
2021-09-01 19:17                                                                             ` Eric Dumazet
2021-09-02  3:59                                                                               ` Vasily Averin
2021-09-02  4:32                                                                                 ` Eric Dumazet
2021-09-02  4:48                                                                                   ` Eric Dumazet
2021-09-02  7:13                                                                                     ` Vasily Averin
2021-09-02  7:33                                                                                       ` Vasily Averin
2021-09-02  8:31                                                                                         ` Vasily Averin
2021-09-02 11:12                                                                                           ` [PATCH net-next v5] " Vasily Averin
2021-09-02 15:53                                                                                             ` Christoph Paasch
2021-09-02 16:32                                                                                               ` Vasily Averin
2021-09-06 18:01                                                                                                 ` [PATCH net v6] " Vasily Averin
2021-09-06 18:03                                                                                                   ` Vasily Averin
2021-08-27 15:23                                                       ` [PATCH NET-NEXT] ipv6: " Vasily Averin
2021-08-27 16:47                                                         ` Eric Dumazet
2021-08-28  8:01                                                           ` Vasily Averin
2021-08-06  7:50                             ` [PATCH NET v4 4/7] ipv4: use skb_expand_head in ip_finish_output2 Vasily Averin
2021-08-06  7:50                             ` [PATCH NET v4 5/7] vrf: use skb_expand_head in vrf_finish_output Vasily Averin
2021-08-06  7:50                             ` [PATCH NET v4 6/7] ax25: use skb_expand_head Vasily Averin
2021-08-06  7:50                             ` [PATCH NET v4 7/7] bpf: use skb_expand_head in bpf_out_neigh_v4/6 Vasily Averin
2021-08-02  8:52                       ` [PATCH NET v3 6/7] ax25: use skb_expand_head Vasily Averin
2021-08-02  8:52                       ` [PATCH NET v3 7/7] bpf: use skb_expand_head in bpf_out_neigh_v4/6 Vasily Averin
     [not found]                   ` <cover.1626206993.git.vvs@virtuozzo.com>
2021-07-13 20:57                     ` [PATCH NET v2 1/7] skbuff: introduce skb_expand_head() Vasily Averin
2021-07-13 20:58                     ` [PATCH NET v2 2/7] ipv6: use skb_expand_head in ip6_finish_output2 Vasily Averin
2021-07-13 20:58                     ` [PATCH NET v2 3/7] ipv6: use skb_expand_head in ip6_xmit Vasily Averin
2021-07-13 20:58                     ` [PATCH NET v2 4/7] ipv4: use skb_expand_head in ip_finish_output2 Vasily Averin
2021-07-13 20:58                     ` [PATCH NET v2 5/7] vrf: use skb_expand_head in vrf_finish_output Vasily Averin
2021-07-13 20:58                     ` [PATCH NET v2 6/7] ax25: use skb_expand_head Vasily Averin
2021-07-13 20:58                     ` [PATCH NET v2 7/7] bpf: use skb_expand_head in bpf_out_neigh_v4/6 Vasily Averin
2021-07-12 13:26             ` [PATCH NET 2/7] ipv6: use pskb_realloc_headroom in ip6_finish_output2 Vasily Averin
2021-07-12 13:26             ` [PATCH NET 3/7] ipv6: use pskb_realloc_headroom in ip6_xmit refactoring Vasily Averin
2021-07-12 13:27             ` [PATCH NET 4/7] ipv4: use pskb_realloc_headroom in ip_finish_output2 Vasily Averin
2021-07-12 13:27             ` [PATCH NET 5/7] vrf: use pskb_realloc_headroom in vrf_finish_output Vasily Averin
2021-07-12 13:27             ` [PATCH NET 6/7] ax25: use pskb_realloc_headroom Vasily Averin
2021-07-12 13:27             ` [PATCH NET 7/7] bpf: use pskb_realloc_headroom in bpf_out_neigh_v4/6 Vasily Averin
     [not found]         ` <cover.1625818825.git.vvs@virtuozzo.com>
2021-07-09  9:04           ` [PATCH IPV6 v2 1/4] ipv6: allocate enough headroom in ip6_finish_output2() Vasily Averin
2021-07-09 17:58             ` David Miller
2021-07-10  2:53               ` Vasily Averin
2021-07-09  9:04           ` [PATCH IPV6 v2 2/4] ipv6: use new helper skb_expand_head() in ip6_xmit() Vasily Averin
2021-07-09  9:05           ` [PATCH IPV6 v2 3/4] ipv6: ip6_finish_output2 refactoring Vasily Averin
2021-07-09  9:05           ` [PATCH IPV6 v2 4/4] ipv6: ip6_xmit refactoring Vasily Averin

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