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 08:59:58 +0300 [thread overview]
Message-ID: <6858f130-e6b4-1ba7-ed6f-58c00152be69@virtuozzo.com> (raw)
In-Reply-To: <7d71f2cc-3fff-beff-b82b-d0a81fb60429@virtuozzo.com>
On 8/23/21 8:44 AM, Vasily Averin wrote:
> 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?
It seems I've found the reason:
before my change pskb_expand_head() is called for newly cloned skb where sk was not set.
after my change skb->sk is set before following pskb_expand_head() call
On own turn pskb_expand_head() adjust truesize:
net/core/skbuff.c::pskb_expand_head()
1751 /* It is not generally safe to change skb->truesize.
1752 * For the moment, we really care of rx path, or
1753 * when skb is orphaned (not attached to a socket).
1754 */
1755 if (!skb->sk || skb->destructor == sock_edemux)
1756 skb->truesize += size - osize;
1757
1758 return 0;
Could you please confirm it?
Thank you,
Vasily Averin
next prev parent reply other threads:[~2021-08-23 6:00 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
2021-08-23 5:59 ` Vasily Averin [this message]
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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