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dgoulet pushed a commit to branch main in repository tor.
commit 13f62582456cc9e7f1e8fd5993dd0e33b7da196b Author: Roger Dingledine arma@torproject.org AuthorDate: Fri Jul 1 15:56:46 2022 -0400
rate-limit low-effort rendezvous responses
specifically, if we have 16 in-flight rend circs, and the next one at the top of the pqueue is lower than our suggested effort, then don't launch it yet.
this way we always launch adequate-effort requests immediately, and we always handle *some* low-effort requests, but we are ready at any moment to handle a few new adequate-effort requests. --- src/feature/hs/hs_circuit.c | 43 ++++++++++++++++++++++++++++++++++++++++++- 1 file changed, 42 insertions(+), 1 deletion(-)
diff --git a/src/feature/hs/hs_circuit.c b/src/feature/hs/hs_circuit.c index 4e31a534b0..c5eb22d5cd 100644 --- a/src/feature/hs/hs_circuit.c +++ b/src/feature/hs/hs_circuit.c @@ -710,12 +710,37 @@ count_service_rp_circuits_pending(hs_service_t *service) return count; }
+/** Peek at the top entry on the pending rend pqueue. If its level of + * effort is at least what we're suggesting for that service right now, + * return 1, else return 0. + */ +static int +top_of_rend_pqueue_is_worthwhile(hs_pow_service_state_t *pow_state) +{ + tor_assert(pow_state->rend_request_pqueue); + tor_assert(smartlist_len(pow_state->rend_request_pqueue)); + + pending_rend_t *req = + smartlist_get(pow_state->rend_request_pqueue, 0); + + if (req->rdv_data.pow_effort >= pow_state->suggested_effort) + return 1; + + return 0; +} + /** How many rendezvous request we handle per mainloop event. Per prop327, * handling an INTRODUCE2 cell takes on average 5.56msec on an average CPU and * so it means that launching this max amount of circuits is well below 0.08 * seconds which we believe is negligable on the whole mainloop. */ #define MAX_REND_REQUEST_PER_MAINLOOP 16
+/** What is the threshold of in-progress (CIRCUIT_PURPOSE_S_CONNECT_REND) + * rendezvous responses above which we won't launch new low-effort rendezvous + * responses? (Intro2 cells with suitable PoW effort are not affected + * by this threshold.) */ +#define MAX_CHEAP_REND_CIRCUITS_IN_PROGRESS 16 + static void handle_rend_pqueue_cb(mainloop_event_t *ev, void *arg) { @@ -723,16 +748,31 @@ handle_rend_pqueue_cb(mainloop_event_t *ev, void *arg) hs_service_t *service = arg; hs_pow_service_state_t *pow_state = service->state.pow_state; time_t now = time(NULL); + int in_flight = count_service_rp_circuits_pending(service);
(void) ev; /* Not using the returned event, make compiler happy. */
log_notice(LD_REND, "Considering launching more rendezvous responses. " "%d in-flight, %d pending.", - count_service_rp_circuits_pending(service), + in_flight, smartlist_len(pow_state->rend_request_pqueue));
/* Process rendezvous request until the maximum per mainloop run. */ while (smartlist_len(pow_state->rend_request_pqueue) > 0) { + + /* first, peek at the top result to see if we want to pop it */ + if (in_flight >= MAX_CHEAP_REND_CIRCUITS_IN_PROGRESS && + !top_of_rend_pqueue_is_worthwhile(pow_state)) { + /* We have queued requests, but they are all low priority, and also + * we have too many in-progress rendezvous responses. Don't launch + * any more. Schedule ourselves to reassess in a bit. */ + log_notice(LD_REND, "Next request to launch is low priority, and " + "%d in-flight already. Waiting to launch more.", in_flight); + const struct timeval delay_tv = { 0, 100000 }; + mainloop_event_schedule(pow_state->pop_pqueue_ev, &delay_tv); + return; /* done here! no cleanup needed. */ + } + /* Pop next request by effort. */ pending_rend_t *req = smartlist_pqueue_pop(pow_state->rend_request_pqueue, @@ -756,6 +796,7 @@ handle_rend_pqueue_cb(mainloop_event_t *ev, void *arg) &req->ip_enc_key_kp, &req->rdv_data, now); free_pending_rend(req);
+ ++in_flight; if (++count == MAX_REND_REQUEST_PER_MAINLOOP) { break; }