Messages in this thread | | | Subject | Re: [PATCH net] net: gro: set the last skb->next to NULL when it get merged | From | Eric Dumazet <> | Date | Wed, 27 Oct 2021 12:25:33 -0700 |
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On 10/27/21 1:07 AM, Jason Xing 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.
GRO only keeps one skb per flow in the main hash/lru.
I think you are not understanding GRO correctly.
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