From: Ilias Apalodimas <ilias.apalodimas@linaro.org>
To: Alexander Duyck <alexander.duyck@gmail.com>
Cc: Yunsheng Lin <linyunsheng@huawei.com>,
Netdev <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>,
LKML <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 17:45:41 +0300 [thread overview]
Message-ID: <YPBKFXWdDytvPmoN@Iliass-MBP> (raw)
In-Reply-To: <CAKgT0UemhFPHo9krmQfm=yNTSjwpBwVkoFtLEEQ-qLVh=-BeHg@mail.gmail.com>
> > > 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?
>
> I don't see how. The assumption here is that when atomic_sub_return
> gets down to 0 we will still have an skb with skb->pp_recycle set and
> it will flow down and encounter skb_free_head below. All we are doing
> is skipping those steps and clearing skb->pp_recycle for all but the
> last buffer and the last one to free it will trigger the recycling.
I think the assumption here is that
1. We clone an skb
2. The original skb goes into pskb_expand_head()
3. skb_release_data() will be called for the original skb
But with the dataref bumped, we'll skip the recycling for it but we'll also
skip recycling or unmapping the current head (which is a page_pool mapped
buffer)
>
> > >
> > > 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;
>
> Note the path here. We don't clear skb->pp_recycle for the last buffer
> where "dataref == 0" until *AFTER* the head has been freed, and all
> clones will have skb->pp_recycle = 1 as long as they are a clone of
> the original skb that had it set.
next prev parent reply other threads:[~2021-07-15 14:45 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-07-09 6:29 [PATCH 1/1 v2] skbuff: Fix a potential race while recycling page_pool packets 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
2021-07-15 12:37 ` Ilias Apalodimas
2021-07-15 14:25 ` Alexander Duyck
2021-07-15 14:45 ` Ilias Apalodimas [this message]
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=YPBKFXWdDytvPmoN@Iliass-MBP \
--to=ilias.apalodimas@linaro.org \
--cc=alexander.duyck@gmail.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=jonathan.lemon@gmail.com \
--cc=kuba@kernel.org \
--cc=linmiaohe@huawei.com \
--cc=linux-kernel@vger.kernel.org \
--cc=linyunsheng@huawei.com \
--cc=mcroce@microsoft.com \
--cc=netdev@vger.kernel.org \
--cc=willemb@google.com \
/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
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
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).