Re: BUG: soft lockup - CPU#6 stuck for 22s! [httpd2-event:15597]
From: Eric Dumazet <hidden>
Date: 2012-08-25 17:52:43
On Sat, 2012-08-25 at 13:47 +0200, Eric Dumazet wrote:
quoted hunk ↗ jump to hunk
On Sat, 2012-08-25 at 11:14 +0200, Eric Dumazet wrote:quoted
From: Eric Dumazet <edumazet@google.com> On Sat, 2012-08-25 at 10:59 +0200, Eric Dumazet wrote:quoted
On Fri, 2012-08-24 at 20:50 -0400, Cristian Rodríguez wrote:quoted
Hi, the issue I reported with IPV6 few weeks ago seems to be gone, but now I am getting the following crash..quoted
Oh, I now see the bug, I'll send a patch asapPlease try the following fix. Thanks !Well, this v2 seems cleaner : [PATCH v2] tcp: tcp_slow_start() should not decrease snd_cwnd Cristian Rodríguez reported various lockups in TCP stack, introduced by commit 9dc274151a548 (tcp: fix ABC in tcp_slow_start()) We could exit tcp_slow_start() with a zeroed snd_cwnd, and next time we enter tcp_slow_start(), we run an infinite loop. Reported-by: Cristian Rodríguez <redacted> Cc: Yuchung Cheng <redacted> Cc: Neal Cardwell <ncardwell@google.com> Signed-off-by: Eric Dumazet <edumazet@google.com> --- net/ipv4/tcp_cong.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)diff --git a/net/ipv4/tcp_cong.c b/net/ipv4/tcp_cong.c index 1432cdb..e656c72 100644 --- a/net/ipv4/tcp_cong.c +++ b/net/ipv4/tcp_cong.c@@ -337,7 +337,7 @@ void tcp_slow_start(struct tcp_sock *tp) tp->snd_cwnd_cnt -= tp->snd_cwnd; delta++; } - tp->snd_cwnd = min(tp->snd_cwnd + delta, tp->snd_cwnd_clamp); + tp->snd_cwnd = clamp(tp->snd_cwnd + delta, tp->snd_cwnd, tp->snd_cwnd_clamp); } EXPORT_SYMBOL_GPL(tcp_slow_start);
Hmm...
We probably have a bug in tcp_metrics.c, because snd_cwnd_clamp should
not be zero.
With RCU, it seems following code in tcpm_new() is racy :
tm->tcpm_addr = *addr;
...
tcpm_suck_dst(tm, dst);
Coupled with the code in tcpm_suck_dst(tm, dst)
static void tcpm_suck_dst(struct tcp_metrics_block *tm, struct dst_entry *dst)
{
u32 val;
tm->tcpm_stamp = jiffies;
val = 0;
if (dst_metric_locked(dst, RTAX_RTT))
val |= 1 << TCP_METRIC_RTT;
if (dst_metric_locked(dst, RTAX_RTTVAR))
val |= 1 << TCP_METRIC_RTTVAR;
if (dst_metric_locked(dst, RTAX_SSTHRESH))
val |= 1 << TCP_METRIC_SSTHRESH;
if (dst_metric_locked(dst, RTAX_CWND))
val |= 1 << TCP_METRIC_CWND;
if (dst_metric_locked(dst, RTAX_REORDERING))
val |= 1 << TCP_METRIC_REORDERING;
tm->tcpm_lock = val;
// HERE we set tcpm_lock before the tcpm_vals[]
tm->tcpm_vals[TCP_METRIC_RTT] = dst_metric_raw(dst, RTAX_RTT);
tm->tcpm_vals[TCP_METRIC_RTTVAR] = dst_metric_raw(dst, RTAX_RTTVAR);
tm->tcpm_vals[TCP_METRIC_SSTHRESH] = dst_metric_raw(dst, RTAX_SSTHRESH);
tm->tcpm_vals[TCP_METRIC_CWND] = dst_metric_raw(dst, RTAX_CWND);
tm->tcpm_vals[TCP_METRIC_REORDERING] = dst_metric_raw(dst, RTAX_REORDERING);
tm->tcpm_ts = 0;
tm->tcpm_ts_stamp = 0;
tm->tcpm_fastopen.mss = 0;
tm->tcpm_fastopen.syn_loss = 0;
tm->tcpm_fastopen.cookie.len = 0;
}