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    SubjectRe: 2.6.24-rc8-mm1 : net tcp_input.c warnings
    On Jan 22, 2008 6:47 PM, Ilpo Järvinen <ilpo.jarvinen@helsinki.fi> wrote:
    >
    > On Tue, 22 Jan 2008, Dave Young wrote:
    >
    > > On Jan 22, 2008 12:37 PM, Dave Young <hidave.darkstar@gmail.com> wrote:
    > > >
    > > > On Jan 22, 2008 5:14 AM, Ilpo Järvinen <ilpo.jarvinen@helsinki.fi> wrote:
    > > > >
    > > > > On Mon, 21 Jan 2008, Dave Young wrote:
    > > > >
    > > > > > Please see the kernel messages following,(trigged while using some qemu session)
    > > > > > BTW, seems there's some e100 error message as well.
    > > > > >
    > > > > > PCI: Setting latency timer of device 0000:00:1b.0 to 64
    > > > > > e100: Intel(R) PRO/100 Network Driver, 3.5.23-k4-NAPI
    > > > > > e100: Copyright(c) 1999-2006 Intel Corporation
    > > > > > ACPI: PCI Interrupt 0000:03:08.0[A] -> GSI 20 (level, low) -> IRQ 20
    > > > > > modprobe:2331 conflicting cache attribute efaff000-efb00000 uncached<->default
    > > > > > e100: 0000:03:08.0: e100_probe: Cannot map device registers, aborting.
    > > > > > ACPI: PCI interrupt for device 0000:03:08.0 disabled
    > > > > > e100: probe of 0000:03:08.0 failed with error -12
    > > > > > eth0: setting full-duplex.
    > > > > > ------------[ cut here ]------------
    > > > > > WARNING: at net/ipv4/tcp_input.c:2169 tcp_mark_head_lost+0x121/0x150()
    > > > > > Modules linked in: snd_seq_dummy snd_seq_oss snd_seq_midi_event snd_seq snd_seq_device snd_pcm_oss snd_mixer_oss eeprom e100 psmouse snd_hda_intel snd_pcm snd_timer btusb rtc_cmos thermal bluetooth rtc_core serio_raw intel_agp button processor sg snd rtc_lib i2c_i801 evdev agpgart soundcore dcdbas 3c59x pcspkr snd_page_alloc
    > > > > > Pid: 0, comm: swapper Not tainted 2.6.24-rc8-mm1 #4
    > > > > > [<c0132100>] ? printk+0x0/0x20
    > > > > > [<c0131834>] warn_on_slowpath+0x54/0x80
    > > > > > [<c03e8df8>] ? ip_finish_output+0x128/0x2e0
    > > > > > [<c03e9527>] ? ip_output+0xe7/0x100
    > > > > > [<c03e8a88>] ? ip_local_out+0x18/0x20
    > > > > > [<c03e991c>] ? ip_queue_xmit+0x3dc/0x470
    > > > > > [<c043641e>] ? _spin_unlock_irqrestore+0x5e/0x70
    > > > > > [<c0186be1>] ? check_pad_bytes+0x61/0x80
    > > > > > [<c03f6031>] tcp_mark_head_lost+0x121/0x150
    > > > > > [<c03f60ac>] tcp_update_scoreboard+0x4c/0x170
    > > > > > [<c03f6e0a>] tcp_fastretrans_alert+0x48a/0x6b0
    > > > > > [<c03f7d93>] tcp_ack+0x1b3/0x3a0
    > > > > > [<c03fa14b>] tcp_rcv_established+0x3eb/0x710
    > > > > > [<c04015c5>] tcp_v4_do_rcv+0xe5/0x100
    > > > > > [<c0401bbb>] tcp_v4_rcv+0x5db/0x660
    > > > >
    > > > > Doh, once more these S+L things..., the rest are symptom of the first
    > > > > problem.
    > > >
    > > > What is the S+L thing? Could you explain a bit?
    >
    > It means that one of the skbs is both SACKed and marked as LOST at the
    > same time in the counters (might be due to miscount of lost/sacked_out
    > too, not necessarilily in the ->sacked bits). Such state is logically
    > invalid because it would mean that the sender thinks that the same packet
    > both reached the receiver and is lost in the network.
    >
    > Traditionally TCP has just silently "corrected" over-estimates
    > (sacked_out+lost_out > packets_out). I changed this couple of releases ago
    > because those over-estimates often are due to bugs that should be fixed
    > (there have been couple of them but it has been very quite on this front
    > long time, months or even half year already; but I might have broken
    > something with the early Dec changes).
    >
    > These problem may originate from a bug that occurred a number of ACKs
    > earlier the WARN_ON triggered, therefore they are a bit tricky to track,
    > those WARN_ON serve just for alerting purposes and usually do not point
    > out where the bug actually occurred.
    >
    > I usually just asked people to include exhaustive verifier which compares
    > ->sacked bitmaps with sacked/lost_out counters and report immediately when
    > the problem shows up, rather than waiting for the cheaper S+L check we do
    > in the WARN_ON to trigger. I tried to collect tracking patch from the
    > previous efforts (hopefully got it right after modifications).
    >
    > > > I'm a bit worried about its
    > > > > reproducability if it takes this far to see it...
    > > > >
    > >
    > > It's trigged again in my pc, just while using firefox.
    >
    > ...Good, then there's some chance to catch it.
    >
    > --
    > i.
    >
    > [PATCH] [TCP]: debug S+L

    Thanks, If there's new findings I will let you know.

    >
    > ---
    > include/net/tcp.h | 8 +++-
    > net/ipv4/tcp_input.c | 6 +++
    > net/ipv4/tcp_ipv4.c | 101 +++++++++++++++++++++++++++++++++++++++++++++++++
    > net/ipv4/tcp_output.c | 21 +++++++---
    > 4 files changed, 129 insertions(+), 7 deletions(-)
    >
    > diff --git a/include/net/tcp.h b/include/net/tcp.h
    > index 7de4ea3..0685035 100644
    > --- a/include/net/tcp.h
    > +++ b/include/net/tcp.h
    > @@ -272,6 +272,8 @@ DECLARE_SNMP_STAT(struct tcp_mib, tcp_statistics);
    > #define TCP_ADD_STATS_BH(field, val) SNMP_ADD_STATS_BH(tcp_statistics, field, val)
    > #define TCP_ADD_STATS_USER(field, val) SNMP_ADD_STATS_USER(tcp_statistics, field, val)
    >
    > +extern void tcp_verify_wq(struct sock *sk);
    > +
    > extern void tcp_v4_err(struct sk_buff *skb, u32);
    >
    > extern void tcp_shutdown (struct sock *sk, int how);
    > @@ -768,7 +770,11 @@ static inline __u32 tcp_current_ssthresh(const struct sock *sk)
    > }
    >
    > /* Use define here intentionally to get WARN_ON location shown at the caller */
    > -#define tcp_verify_left_out(tp) WARN_ON(tcp_left_out(tp) > tp->packets_out)
    > +#define tcp_verify_left_out(tp) \
    > + do { \
    > + WARN_ON(tcp_left_out(tp) > tp->packets_out); \
    > + tcp_verify_wq((struct sock *)tp); \
    > + } while(0)
    >
    > extern void tcp_enter_cwr(struct sock *sk, const int set_ssthresh);
    > extern __u32 tcp_init_cwnd(struct tcp_sock *tp, struct dst_entry *dst);
    > diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
    > index fa2c85c..0bda0e1 100644
    > --- a/net/ipv4/tcp_input.c
    > +++ b/net/ipv4/tcp_input.c
    > @@ -2645,6 +2645,10 @@ static void tcp_fastretrans_alert(struct sock *sk, int pkts_acked, int flag)
    > if (do_lost || (tcp_is_fack(tp) && tcp_head_timedout(sk)))
    > tcp_update_scoreboard(sk, fast_rexmit);
    > tcp_cwnd_down(sk, flag);
    > +
    > + WARN_ON(tcp_write_queue_head(sk) == NULL);
    > + WARN_ON(!tp->packets_out);
    > +
    > tcp_xmit_retransmit_queue(sk);
    > }
    >
    > @@ -2848,6 +2852,8 @@ static int tcp_clean_rtx_queue(struct sock *sk, int prior_fackets)
    > tcp_clear_all_retrans_hints(tp);
    > }
    >
    > + tcp_verify_left_out(tp);
    > +
    > if (skb && (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED))
    > flag |= FLAG_SACK_RENEGING;
    >
    > diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c
    > index 9aea88b..21f5888 100644
    > --- a/net/ipv4/tcp_ipv4.c
    > +++ b/net/ipv4/tcp_ipv4.c
    > @@ -108,6 +108,107 @@ struct inet_hashinfo __cacheline_aligned tcp_hashinfo = {
    > .lhash_wait = __WAIT_QUEUE_HEAD_INITIALIZER(tcp_hashinfo.lhash_wait),
    > };
    >
    > +void tcp_print_queue(struct sock *sk)
    > +{
    > + struct tcp_sock *tp = tcp_sk(sk);
    > + struct sk_buff *skb;
    > + char s[50+1];
    > + char h[50+1];
    > + int idx = 0;
    > + int i;
    > +
    > + tcp_for_write_queue(skb, sk) {
    > + if (skb == tcp_send_head(sk))
    > + break;
    > +
    > + for (i = 0; i < tcp_skb_pcount(skb); i++) {
    > + if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED) {
    > + s[idx] = 'S';
    > + if (TCP_SKB_CB(skb)->sacked & TCPCB_LOST)
    > + s[idx] = 'B';
    > +
    > + } else if (TCP_SKB_CB(skb)->sacked & TCPCB_LOST) {
    > + s[idx] = 'L';
    > + } else {
    > + s[idx] = ' ';
    > + }
    > + if (s[idx] != ' ' && skb->len < tp->mss_cache)
    > + s[idx] += 'a' - 'A';
    > +
    > + if (i == 0) {
    > + if (TCP_SKB_CB(skb)->seq == tcp_highest_sack_seq(tp))
    > + h[idx] = 'h';
    > + else
    > + h[idx] = '+';
    > + } else {
    > + h[idx] = '-';
    > + }
    > +
    > + if (++idx >= 50) {
    > + s[idx] = 0;
    > + h[idx] = 0;
    > + printk(KERN_ERR "TCP wq(s) %s\n", s);
    > + printk(KERN_ERR "TCP wq(h) %s\n", h);
    > + idx = 0;
    > + }
    > + }
    > + }
    > + if (idx) {
    > + s[idx] = '<';
    > + s[idx+1] = 0;
    > + h[idx] = '<';
    > + h[idx+1] = 0;
    > + printk(KERN_ERR "TCP wq(s) %s\n", s);
    > + printk(KERN_ERR "TCP wq(h) %s\n", h);
    > + }
    > + printk(KERN_ERR "l%u s%u f%u p%u seq: su%u hs%u sn%u\n",
    > + tp->lost_out, tp->sacked_out, tp->fackets_out, tp->packets_out,
    > + tp->snd_una, tcp_highest_sack_seq(tp), tp->snd_nxt);
    > +}
    > +
    > +void tcp_verify_wq(struct sock *sk)
    > +{
    > + struct tcp_sock *tp = tcp_sk(sk);
    > + u32 lost = 0;
    > + u32 sacked = 0;
    > + u32 packets = 0;
    > + struct sk_buff *skb;
    > +
    > + tcp_for_write_queue(skb, sk) {
    > + if (skb == tcp_send_head(sk))
    > + break;
    > +
    > + if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED) {
    > + sacked += tcp_skb_pcount(skb);
    > + if (TCP_SKB_CB(skb)->sacked & TCPCB_LOST)
    > + printk(KERN_ERR "Sacked bitmap S+L: %u %u-%u/%u\n",
    > + TCP_SKB_CB(skb)->sacked,
    > + TCP_SKB_CB(skb)->end_seq - tp->snd_una,
    > + TCP_SKB_CB(skb)->seq - tp->snd_una,
    > + tp->snd_una);
    > + }
    > + if (TCP_SKB_CB(skb)->sacked & TCPCB_LOST)
    > + lost += tcp_skb_pcount(skb);
    > +
    > + packets += tcp_skb_pcount(skb);
    > + }
    > +
    > + WARN_ON(lost != tp->lost_out);
    > + WARN_ON(sacked != tp->sacked_out);
    > + WARN_ON(packets != tp->packets_out);
    > + if ((lost != tp->lost_out) ||
    > + (sacked != tp->sacked_out) ||
    > + (packets != tp->packets_out)) {
    > + printk(KERN_ERR "P: %u L: %u vs %u S: %u vs %u w: %u-%u (%u)\n",
    > + tp->packets_out,
    > + lost, tp->lost_out,
    > + sacked, tp->sacked_out,
    > + tp->snd_una, tp->snd_nxt,
    > + tp->rx_opt.sack_ok);
    > + tcp_print_queue(sk);
    > + }
    > +}
    > +
    > static int tcp_v4_get_port(struct sock *sk, unsigned short snum)
    > {
    > return inet_csk_get_port(&tcp_hashinfo, sk, snum,
    > diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
    > index 89f0188..648340f 100644
    > --- a/net/ipv4/tcp_output.c
    > +++ b/net/ipv4/tcp_output.c
    > @@ -779,10 +779,9 @@ int tcp_fragment(struct sock *sk, struct sk_buff *skb, u32 len,
    > tp->lost_out -= diff;
    >
    > /* Adjust Reno SACK estimate. */
    > - if (tcp_is_reno(tp) && diff > 0) {
    > + if (tcp_is_reno(tp) && diff > 0)
    > tcp_dec_pcount_approx_int(&tp->sacked_out, diff);
    > - tcp_verify_left_out(tp);
    > - }
    > +
    > tcp_adjust_fackets_out(sk, skb, diff);
    > }
    >
    > @@ -790,6 +789,8 @@ int tcp_fragment(struct sock *sk, struct sk_buff *skb, u32 len,
    > skb_header_release(buff);
    > tcp_insert_write_queue_after(skb, buff, sk);
    >
    > + tcp_verify_left_out(tp);
    > +
    > return 0;
    > }
    >
    > @@ -1463,6 +1464,7 @@ static int tcp_write_xmit(struct sock *sk, unsigned int mss_now, int nonagle)
    > } else if (result > 0) {
    > sent_pkts = 1;
    > }
    > + tcp_verify_left_out(tp);
    >
    > while ((skb = tcp_send_head(sk))) {
    > unsigned int limit;
    > @@ -1764,6 +1766,7 @@ static void tcp_retrans_try_collapse(struct sock *sk, struct sk_buff *skb,
    > tcp_clear_retrans_hints_partial(tp);
    >
    > sk_wmem_free_skb(sk, next_skb);
    > + tcp_verify_left_out(tp);
    > }
    >
    > /* Do a simple retransmit without using the backoff mechanisms in
    > @@ -1795,13 +1798,13 @@ void tcp_simple_retransmit(struct sock *sk)
    > }
    > }
    >
    > + tcp_verify_left_out(tp);
    > +
    > tcp_clear_all_retrans_hints(tp);
    >
    > if (!lost)
    > return;
    >
    > - tcp_verify_left_out(tp);
    > -
    > /* Don't muck with the congestion window here.
    > * Reason is that we do not increase amount of _data_
    > * in network, but units changed and effective
    > @@ -1970,8 +1973,10 @@ void tcp_xmit_retransmit_queue(struct sock *sk)
    > * packet to be MSS sized and all the
    > * packet counting works out.
    > */
    > - if (tcp_packets_in_flight(tp) >= tp->snd_cwnd)
    > + if (tcp_packets_in_flight(tp) >= tp->snd_cwnd) {
    > + tcp_verify_left_out(tp);
    > return;
    > + }
    >
    > if (sacked & TCPCB_LOST) {
    > if (!(sacked & (TCPCB_SACKED_ACKED|TCPCB_SACKED_RETRANS))) {
    > @@ -1997,6 +2002,8 @@ void tcp_xmit_retransmit_queue(struct sock *sk)
    > }
    > }
    >
    > + tcp_verify_left_out(tp);
    > +
    > /* OK, demanded retransmission is finished. */
    >
    > /* Forward retransmissions are possible only during Recovery. */
    > @@ -2054,6 +2061,8 @@ void tcp_xmit_retransmit_queue(struct sock *sk)
    >
    > NET_INC_STATS_BH(LINUX_MIB_TCPFORWARDRETRANS);
    > }
    > +
    > + tcp_verify_left_out(tp);
    > }
    >
    > /* Send a fin. The caller locks the socket for us. This cannot be
    > --
    > 1.5.2.2
    >
    --
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