Messages in this thread Patch in this message | | | Date | Fri, 09 Jan 2009 23:02:06 +0100 | From | Eric Dumazet <> | Subject | Re: [PATCH] tcp: splice as many packets as possible at once |
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Willy Tarreau a écrit : > On Fri, Jan 09, 2009 at 09:51:17PM +0100, Eric Dumazet wrote: > (...) >>> Also, in your second mail, you're saying that your change >>> might return more data than requested by the user. I can't >>> find why, could you please explain to me, as I'm still quite >>> ignorant in this area ? >> Well, I just tested various user programs and indeed got this >> strange result : >> >> Here I call splice() with len=1000 (0x3e8), and you can see >> it gives a result of 1460 at the second call. > > huh, not nice indeed! > > While looking at the code to see how this could be possible, I > came across this minor thing (unrelated IMHO) : > > if (__skb_splice_bits(skb, &offset, &tlen, &spd)) > goto done; >>>>>>> else if (!tlen) <<<<<< > goto done; > > /* > * now see if we have a frag_list to map > */ > if (skb_shinfo(skb)->frag_list) { > struct sk_buff *list = skb_shinfo(skb)->frag_list; > > for (; list && tlen; list = list->next) { > if (__skb_splice_bits(list, &offset, &tlen, &spd)) > break; > } > } > > done: > > Above on the enlighted line, we'd better remove the else and leave a plain > "if (!tlen)". Otherwise, when the first call to __skb_splice_bits() zeroes > tlen, we still enter the if and evaluate the for condition for nothing. But > let's leave that for later. > >> I suspect a bug in splice code, that my patch just exposed. > > I've checked in skb_splice_bits() and below and can't see how we can move > more than the requested len. > > However, with your change, I don't clearly see how we break out of > the loop in tcp_read_sock(). Maybe we first read 1000 then loop again > and read remaining data ? I suspect that we should at least exit when > ((struct tcp_splice_state *)desc->arg.data)->len = 0. > > At least that's something easy to add just before or after !desc->count > for a test. >
I believe the bug is in tcp_splice_data_recv()
I am going to test a new patch, but here is the thing I found:
diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c index bd6ff90..fbbddf4 100644 --- a/net/ipv4/tcp.c +++ b/net/ipv4/tcp.c @@ -523,7 +523,7 @@ static int tcp_splice_data_recv(read_descriptor_t *rd_desc, struct sk_buff *skb, { struct tcp_splice_state *tss = rd_desc->arg.data;
- return skb_splice_bits(skb, offset, tss->pipe, tss->len, tss->flags); + return skb_splice_bits(skb, offset, tss->pipe, len, tss->flags); }
static int __tcp_splice_read(struct sock *sk, struct tcp_splice_state *tss)
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