| Message ID | 4967C95E.3070602@cosmosbay.com |
|---|---|
| State | RFC, archived |
| Delegated to: | David Miller |
| Headers | show |
On Fri, Jan 09, 2009 at 11:02:06PM +0100, Eric Dumazet wrote: > 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() yes, see my other mail. > 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); > } it will not work, len is always 1000 in your case, for every call, as I had in my logs : kernel : tcp_splice_data_recv: skb=ed3d3480 offset=0 len=1460 tss->pipe=ed1cbc00 tss->len=1000 tss->flags=3 tcp_sendpage: going through do_tcp_sendpages tcp_splice_data_recv: skb=ed3d3480 offset=1000 len=460 tss->pipe=ed1cbc00 tss->len=1000 tss->flags=3 tcp_splice_data_recv: skb=ed3d3540 offset=0 len=1460 tss->pipe=ed1cbc00 tss->len=1000 tss->flags=3 tcp_sendpage: going through do_tcp_sendpages tcp_sendpage: going through do_tcp_sendpages tcp_splice_data_recv: skb=ed3d3540 offset=1000 len=460 tss->pipe=ed1cbc00 tss->len=1000 tss->flags=3 tcp_splice_data_recv: skb=ed3d3600 offset=0 len=1176 tss->pipe=ed1cbc00 tss->len=1000 tss->flags=3 tcp_sendpage: going through do_tcp_sendpages tcp_sendpage: going through do_tcp_sendpages tcp_splice_data_recv: skb=ed3d3600 offset=1000 len=176 tss->pipe=ed1cbc00 tss->len=1000 tss->flags=3 tcp_sendpage: going through do_tcp_sendpages program : accept(3, 0, NULL) = 4 socket(PF_INET, SOCK_STREAM, IPPROTO_TCP) = 5 connect(5, {sa_family=AF_INET, sin_port=htons(4001), sin_addr=inet_addr("10.0.3.1")}, 16) = 0 fcntl64(4, F_SETFL, O_RDONLY|O_NONBLOCK) = 0 fcntl64(5, F_SETFL, O_RDONLY|O_NONBLOCK) = 0 pipe([6, 7]) = 0 select(6, [5], [], NULL, NULL) = 1 (in [5]) splice(0x5, 0, 0x7, 0, 0x3e8, 0x3) = 1000 select(6, [5], [4], NULL, NULL) = 2 (in [5], out [4]) splice(0x6, 0, 0x4, 0, 0x3e8, 0x3) = 1000 splice(0x5, 0, 0x7, 0, 0x3e8, 0x3) = 1460 select(6, [5], [4], NULL, NULL) = 2 (in [5], out [4]) splice(0x6, 0, 0x4, 0, 0x5b4, 0x3) = 1460 splice(0x5, 0, 0x7, 0, 0x3e8, 0x3) = 1460 select(6, [5], [4], NULL, NULL) = 2 (in [5], out [4]) splice(0x6, 0, 0x4, 0, 0x5b4, 0x3) = 1460 splice(0x5, 0, 0x7, 0, 0x3e8, 0x3) = 176 select(6, [5], [4], NULL, NULL) = 2 (in [5], out [4]) splice(0x6, 0, 0x4, 0, 0xb0, 0x3) = 176 splice(0x5, 0, 0x7, 0, 0x3e8, 0x3) = -1 EAGAIN (Resource temporarily unavailable) close(5) = 0 close(4) = 0 exit_group(0) = ? Now with the fix : accept(3, 0, NULL) = 4 socket(PF_INET, SOCK_STREAM, IPPROTO_TCP) = 5 connect(5, {sa_family=AF_INET, sin_port=htons(4001), sin_addr=inet_addr("10.0.3.1")}, 16) = 0 fcntl64(4, F_SETFL, O_RDONLY|O_NONBLOCK) = 0 fcntl64(5, F_SETFL, O_RDONLY|O_NONBLOCK) = 0 pipe([6, 7]) = 0 select(6, [5], [], NULL, NULL) = 1 (in [5]) splice(0x5, 0, 0x7, 0, 0x3e8, 0x3) = 1000 select(6, [5], [4], NULL, NULL) = 2 (in [5], out [4]) splice(0x6, 0, 0x4, 0, 0x3e8, 0x3) = 1000 splice(0x5, 0, 0x7, 0, 0x3e8, 0x3) = 1000 select(6, [5], [4], NULL, NULL) = 2 (in [5], out [4]) splice(0x6, 0, 0x4, 0, 0x3e8, 0x3) = 1000 splice(0x5, 0, 0x7, 0, 0x3e8, 0x3) = 1000 select(6, [5], [4], NULL, NULL) = 2 (in [5], out [4]) splice(0x6, 0, 0x4, 0, 0x3e8, 0x3) = 1000 splice(0x5, 0, 0x7, 0, 0x3e8, 0x3) = 1000 select(6, [5], [4], NULL, NULL) = 2 (in [5], out [4]) splice(0x6, 0, 0x4, 0, 0x3e8, 0x3) = 1000 splice(0x5, 0, 0x7, 0, 0x3e8, 0x3) = 96 select(6, [5], [4], NULL, NULL) = 2 (in [5], out [4]) splice(0x6, 0, 0x4, 0, 0x60, 0x3) = 96 splice(0x5, 0, 0x7, 0, 0x3e8, 0x3) = -1 EAGAIN (Resource temporarily unavailable) close(5) = 0 close(4) = 0 exit_group(0) = ? Regards, Willy -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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)