Messages in this thread | | | From | Ilias Apalodimas <> | Date | Thu, 15 Jul 2021 13:38:07 +0300 | Subject | Re: [PATCH 1/1 v2] skbuff: Fix a potential race while recycling page_pool packets |
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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?
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; > > > } > > > > > > /* > > >
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