tcp: improve handling of stopped timers

[tuexen]

Summary

When a TCP timer is stopped, t_timers[] is set to SBT_MAX. Adding the corresponding t_precisions[] would result in overflows in tcp_timer_next(). To avoid this, skip stopped timers.

The problem was identified while debugging uperf by Lukas Book and an initial patch was provided by him. The problem can be observed by running netstat -nxptcp and looking for negative timer values.

[glebius]

sys/netinet/tcp_timer.c

860–861

Alternative patch. I'd prefer this one as it is less memory writes on timer stop. The cycle still needs to put the tp->t_timers[i] in the register anyway.

[tuexen]

sys/netinet/tcp_timer.c

860–861

Makes sense. Will update the patch after testing it.

[tuexen]

As suggested by glebius.

[glebius]

Thanks and sorry for this bug :)