commit 8f9cf1ec4341f23c6a09c4f8194eb0c546cdb187 Author: Mike Perry mikeperry-git@torproject.org Date: Fri Aug 20 15:44:16 2021 +0000

Export a global notion of monotime clock stall/jump.

Monotime clock functionality is a global property, and flow control also needs to know if it can trust the clock. --- src/core/or/congestion_control_common.c | 54 +++++++++++++++++++++++++-------- src/core/or/congestion_control_common.h | 1 + 2 files changed, 43 insertions(+), 12 deletions(-)

diff --git a/src/core/or/congestion_control_common.c b/src/core/or/congestion_control_common.c index 9db1d7d664..edb65d2b70 100644 --- a/src/core/or/congestion_control_common.c +++ b/src/core/or/congestion_control_common.c @@ -558,10 +558,16 @@ time_delta_should_use_heuristics(const congestion_control_t *cc) return false; }

+static bool is_monotime_clock_broken = false; + /** * Returns true if the monotime delta is 0, or is significantly * different than the previous delta. Either case indicates * that the monotime time source stalled or jumped. + * + * Also caches the clock state in the is_monotime_clock_broken flag, + * so we can also provide a is_monotime_clock_reliable() function, + * used by flow control rate timing. */ static bool time_delta_stalled_or_jumped(const congestion_control_t *cc, @@ -573,22 +579,30 @@ time_delta_stalled_or_jumped(const congestion_control_t *cc, static ratelim_t stall_info_limit = RATELIM_INIT(60); log_fn_ratelim(&stall_info_limit, LOG_INFO, LD_CIRC, "Congestion control cannot measure RTT due to monotime stall."); - return true; + + /* If delta is every 0, the monotime clock has stalled, and we should + * not use it anywhere. */ + is_monotime_clock_broken = true; + + return is_monotime_clock_broken; }

- /* If the old_delta is 0, we have no previous values. So - * just assume this one is valid (beause it is non-zero) */ - if (old_delta == 0) - return false; + /* If the old_delta is 0, we have no previous values on this circuit. + * + * So, return the global monotime status from other circuits, and + * do not update. + */ + if (old_delta == 0) { + return is_monotime_clock_broken; + }

/* * For the heuristic cases, we need at least a few timestamps, * to average out any previous partial stalls or jumps. So until - * than point, let's just delcare these time values "good enough - * to use". + * than point, let's just use the cached status from other circuits. */ if (!time_delta_should_use_heuristics(cc)) { - return false; + return is_monotime_clock_broken; }

/* If old_delta is significantly larger than new_delta, then @@ -601,7 +615,9 @@ time_delta_stalled_or_jumped(const congestion_control_t *cc, "), likely due to clock jump.", new_delta/1000, old_delta/1000);

- return true; + is_monotime_clock_broken = true; + + return is_monotime_clock_broken; }

/* If new_delta is significantly larger than old_delta, then @@ -613,10 +629,24 @@ time_delta_stalled_or_jumped(const congestion_control_t *cc, "), likely due to clock jump.", new_delta/1000, old_delta/1000);

- return true; + is_monotime_clock_broken = true; + + return is_monotime_clock_broken; }

- return false; + /* All good! Update cached status, too */ + is_monotime_clock_broken = false; + + return is_monotime_clock_broken; +} + +/** + * Is the monotime clock stalled according to any circuits? + */ +bool +is_monotime_clock_reliable(void) +{ + return !is_monotime_clock_broken; }

/** @@ -753,7 +783,7 @@ congestion_control_update_circuit_bdp(congestion_control_t *cc, SMARTLIST_FOREACH(cc->sendme_arrival_timestamps, uint64_t *, t, tor_free(t)); smartlist_clear(cc->sendme_arrival_timestamps); - } else if (curr_rtt_usec) { + } else if (curr_rtt_usec && is_monotime_clock_reliable()) { /* Sendme-based BDP will quickly measure BDP in much less than * a cwnd worth of data when in use (in 2-10 SENDMEs). * diff --git a/src/core/or/congestion_control_common.h b/src/core/or/congestion_control_common.h index 4193d94cba..12da0cb4e0 100644 --- a/src/core/or/congestion_control_common.h +++ b/src/core/or/congestion_control_common.h @@ -39,6 +39,7 @@ int congestion_control_get_package_window(const circuit_t *,

int sendme_get_inc_count(const circuit_t *, const crypt_path_t *); bool circuit_sent_cell_for_sendme(const circuit_t *, const crypt_path_t *); +bool is_monotime_clock_reliable(void);

/* Private section starts. */ #ifdef TOR_CONGESTION_CONTROL_PRIVATE