Netdev Archive on lore.kernel.org
help / color / mirror / Atom feed
From: Yunsheng Lin <linyunsheng@huawei.com>
To: Ilias Apalodimas <ilias.apalodimas@linaro.org>
Cc: Networking <netdev@vger.kernel.org>,
	Alexander Duyck <alexanderduyck@fb.com>,
	"David S. Miller" <davem@davemloft.net>,
	"Jakub Kicinski" <kuba@kernel.org>,
	Alexander Lobakin <alobakin@pm.me>,
	"Jonathan Lemon" <jonathan.lemon@gmail.com>,
	Willem de Bruijn <willemb@google.com>,
	Miaohe Lin <linmiaohe@huawei.com>,
	Guillaume Nault <gnault@redhat.com>,
	"Cong Wang" <cong.wang@bytedance.com>,
	Jesper Dangaard Brouer <brouer@redhat.com>,
	Matteo Croce <mcroce@microsoft.com>,
	open list <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 1/1 v2] skbuff: Fix a potential race while recycling page_pool packets
Date: Thu, 15 Jul 2021 18:47:55 +0800	[thread overview]
Message-ID: <401f10b2-3b92-a3f9-f01e-df2e190c8ff3@huawei.com> (raw)
In-Reply-To: <CAC_iWjLfsvr_Z2te=ABfEAecAOkQBiu22QZ8GhorA4MYnt4Uxg@mail.gmail.com>

On 2021/7/15 18:38, Ilias Apalodimas wrote:
> On Thu, 15 Jul 2021 at 13:00, Ilias Apalodimas
> <ilias.apalodimas@linaro.org> wrote:
>>
>> On Thu, 15 Jul 2021 at 07:01, Yunsheng Lin <linyunsheng@huawei.com> wrote:
>>>
>>> On 2021/7/9 14:29, Ilias Apalodimas wrote:
>>>> As Alexander points out, when we are trying to recycle a cloned/expanded
>>>> SKB we might trigger a race.  The recycling code relies on the
>>>> pp_recycle bit to trigger,  which we carry over to cloned SKBs.
>>>> If that cloned SKB gets expanded or if we get references to the frags,
>>>> call skbb_release_data() and overwrite skb->head, we are creating separate
>>>> instances accessing the same page frags.  Since the skb_release_data()
>>>> will first try to recycle the frags,  there's a potential race between
>>>> the original and cloned SKB, since both will have the pp_recycle bit set.
>>>>
>>>> Fix this by explicitly those SKBs not recyclable.
>>>> The atomic_sub_return effectively limits us to a single release case,
>>>> and when we are calling skb_release_data we are also releasing the
>>>> option to perform the recycling, or releasing the pages from the page pool.
>>>>
>>>> Fixes: 6a5bcd84e886 ("page_pool: Allow drivers to hint on SKB recycling")
>>>> Reported-by: Alexander Duyck <alexanderduyck@fb.com>
>>>> Suggested-by: Alexander Duyck <alexanderduyck@fb.com>
>>>> Signed-off-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>
>>>> ---
>>>> Changes since v1:
>>>> - Set the recycle bit to 0 during skb_release_data instead of the
>>>>   individual fucntions triggering the issue, in order to catch all
>>>>   cases
>>>>  net/core/skbuff.c | 4 +++-
>>>>  1 file changed, 3 insertions(+), 1 deletion(-)
>>>>
>>>> diff --git a/net/core/skbuff.c b/net/core/skbuff.c
>>>> index 12aabcda6db2..f91f09a824be 100644
>>>> --- a/net/core/skbuff.c
>>>> +++ b/net/core/skbuff.c
>>>> @@ -663,7 +663,7 @@ static void skb_release_data(struct sk_buff *skb)
>>>>       if (skb->cloned &&
>>>>           atomic_sub_return(skb->nohdr ? (1 << SKB_DATAREF_SHIFT) + 1 : 1,
>>>>                             &shinfo->dataref))
>>>> -             return;
>>>> +             goto exit;
>>>
>>> Is it possible this patch may break the head frag page for the original skb,
>>> supposing it's head frag page is from the page pool and below change clears
>>> the pp_recycle for original skb, causing a page leaking for the page pool?
>>>
>>
>> So this would leak eventually dma mapping if the skb is cloned (and
>> the dataref is now +1) and we are freeing the original skb first?
>>
> 
> Apologies for the noise, my description was not complete.
> The case you are thinking is clone an SKB and then expand the original?

Yes.
It seems we might need different pp_recycle bit for head frag and data frag.

> 
> thanks
> /Ilias
> 
> 
>>>>
>>>>       skb_zcopy_clear(skb, true);
>>>>
>>>> @@ -674,6 +674,8 @@ static void skb_release_data(struct sk_buff *skb)
>>>>               kfree_skb_list(shinfo->frag_list);
>>>>
>>>>       skb_free_head(skb);
>>>> +exit:
>>>> +     skb->pp_recycle = 0;
>>>>  }
>>>>
>>>>  /*
>>>>
> .
> 

  reply	other threads:[~2021-07-15 10:48 UTC|newest]

Thread overview: 15+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-07-09  6:29 Ilias Apalodimas
2021-07-09 14:34 ` Alexander Duyck
2021-07-09 17:29   ` Ilias Apalodimas
2021-07-12 11:52   ` Jesper Dangaard Brouer
2021-07-15  4:00 ` Yunsheng Lin
2021-07-15 10:00   ` Ilias Apalodimas
2021-07-15 10:38     ` Ilias Apalodimas
2021-07-15 10:47       ` Yunsheng Lin [this message]
2021-07-15 12:37         ` Ilias Apalodimas
2021-07-15 14:25   ` Alexander Duyck
2021-07-15 14:45     ` Ilias Apalodimas
2021-07-15 14:57       ` Alexander Duyck
2021-07-15 15:02         ` Ilias Apalodimas
2021-07-16  2:30           ` Yunsheng Lin
2021-07-16  6:43             ` Ilias Apalodimas

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=401f10b2-3b92-a3f9-f01e-df2e190c8ff3@huawei.com \
    --to=linyunsheng@huawei.com \
    --cc=alexanderduyck@fb.com \
    --cc=alobakin@pm.me \
    --cc=brouer@redhat.com \
    --cc=cong.wang@bytedance.com \
    --cc=davem@davemloft.net \
    --cc=gnault@redhat.com \
    --cc=ilias.apalodimas@linaro.org \
    --cc=jonathan.lemon@gmail.com \
    --cc=kuba@kernel.org \
    --cc=linmiaohe@huawei.com \
    --cc=linux-kernel@vger.kernel.org \
    --cc=mcroce@microsoft.com \
    --cc=netdev@vger.kernel.org \
    --cc=willemb@google.com \
    --subject='Re: [PATCH 1/1 v2] skbuff: Fix a potential race while recycling page_pool packets' \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).