Messages in this thread | | | From | Jason Xing <> | Date | Wed, 27 Oct 2021 16:56:28 +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 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.
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/
Thanks again, Jason
> > > it is really odd. > > > > Thanks, > > Jason > > > > > __skb_header_release(skb); > > > lp = p; > > > -- > > > 1.8.3.1 > > >
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