Messages in this thread | | | From | Jason Xing <> | Date | Wed, 27 Oct 2021 21:57:40 +0800 | Subject | Re: [PATCH net] net: gro: set the last skb->next to NULL when it get merged |
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On Wed, Oct 27, 2021 at 8:54 PM Jason Xing <kerneljasonxing@gmail.com> wrote: > > On Wed, Oct 27, 2021 at 8:40 PM Yunsheng Lin <linyunsheng@huawei.com> wrote: > > > > On 2021/10/27 16:56, Jason Xing wrote: > > > On Wed, Oct 27, 2021 at 4:07 PM Jason Xing <kerneljasonxing@gmail.com> wrote: > > >> > > >> On Wed, Oct 27, 2021 at 3:23 PM Jason Xing <kerneljasonxing@gmail.com> wrote: > > >>> > > >>> On Tue, Oct 26, 2021 at 9:19 PM <kerneljasonxing@gmail.com> wrote: > > >>>> > > >>>> From: Jason Xing <xingwanli@kuaishou.com> > > >>>> > > >>>> Setting the @next of the last skb to NULL to prevent the panic in future > > >>>> when someone does something to the last of the gro list but its @next is > > >>>> invalid. > > >>>> > > >>>> For example, without the fix (commit: ece23711dd95), a panic could happen > > >>>> with the clsact loaded when skb is redirected and then validated in > > >>>> validate_xmit_skb_list() which could access the error addr of the @next > > >>>> of the last skb. Thus, "general protection fault" would appear after that. > > >>>> > > >>>> Signed-off-by: Jason Xing <xingwanli@kuaishou.com> > > >>>> --- > > >>>> net/core/skbuff.c | 1 + > > >>>> 1 file changed, 1 insertion(+) > > >>>> > > >>>> diff --git a/net/core/skbuff.c b/net/core/skbuff.c > > >>>> index 2170bea..7b248f1 100644 > > >>>> --- a/net/core/skbuff.c > > >>>> +++ b/net/core/skbuff.c > > >>>> @@ -4396,6 +4396,7 @@ int skb_gro_receive(struct sk_buff *p, struct sk_buff *skb) > > >>>> skb_shinfo(p)->frag_list = skb; > > >>>> else > > >>>> NAPI_GRO_CB(p)->last->next = skb; > > >>>> + skb->next = NULL; > > >>>> NAPI_GRO_CB(p)->last = skb; > > >>> > > >>> Besides, I'm a little bit confused that this operation inserts the > > >>> newest skb into the tail of the flow, so the tail of flow is the > > >>> newest, head oldest. The patch (commit: 600adc18) introduces the flush > > >>> of the oldest when the flow is full to lower the latency, but actually > > >>> it fetches the tail of the flow. Do I get something wrong here? I feel > > >> > > >> I have to update this part. The commit 600adc18 evicts and flushes the > > >> oldest flow. But for the current kernel, when > > >> "napi->gro_hash[hash].count >= MAX_GRO_SKBS" happens, the > > >> gro_flush_oldest() flushes the oldest skb of one certain flow, > > >> actually it is the newest skb because it is at the end of the list. > > > > it seems the below is more matched with the gro_flush_oldest() instead > > of the above code block: > > https://elixir.bootlin.com/linux/v5.15-rc3/source/net/core/dev.c#L6118 > > > > What you said is the @skb->list but not the list between skbs which is > connected by skb->next when the new incoming skb needs to get merged. > The @skb->list->next/prev is not the same as @skb->next. > > > > > > > I just submitted another patch to explain how it happens, please help > > > me review both patches. > > > > > > Link: https://lore.kernel.org/lkml/20211027084944.4508-1-kerneljasonxing@gmail.com/ > > >
Emm, I think you're right, Yunsheng. The gro_flush_oldest() fetches the list of @skb->list. Do you think the tail of skb's next pointer should be set to NULL?
Thanks, Jason
> > > Thanks again, > > > Jason > > > > > >> > > >>> it is really odd. > > >>> > > >>> Thanks, > > >>> Jason > > >>> > > >>>> __skb_header_release(skb); > > >>>> lp = p; > > >>>> -- > > >>>> 1.8.3.1 > > >>>> > > > . > > >
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