From: Nick Mathewson <nickm@torproject.org>
Date: Tue, 12 Oct 2010 17:46:14 +0000 (-0400)
Subject: Fix serious bugs in per-bufferevent rate-limiting code
X-Git-Tag: release-2.0.8-rc~14
X-Git-Url: https://granicus.if.org/sourcecode?a=commitdiff_plain;h=34d64f8a347147aa5a6ac222f302e12b142a8f2e;p=libevent

Fix serious bugs in per-bufferevent rate-limiting code

Our old code was too zealous about deleting the refill events that
would actually make connections able to read or write again after
they had run out of bandwidth.  Under some circumstances, this could
cause a bufferevent to never actually refill one of its
rate-limiting buckets.

Also, the code treated setting a per-connection rate-limit on a
connection that already had a group-limit as if it were changing the
limit on a connection whose allocation had already run out.

This patch fixes both of those problems.
---

diff --git a/bufferevent_ratelim.c b/bufferevent_ratelim.c
index 814fcf79..a70cd8db 100644
--- a/bufferevent_ratelim.c
+++ b/bufferevent_ratelim.c
@@ -543,15 +543,19 @@ bufferevent_set_rate_limit(struct bufferevent *bev,
 	struct bufferevent_rate_limit *rlim;
 	struct timeval now;
 	ev_uint32_t tick;
+	int reinit = 0, suspended = 0;
 	/* XXX reference-count cfg */
 
 	BEV_LOCK(bev);
 
 	if (cfg == NULL) {
 		if (bevp->rate_limiting) {
-			bevp->rate_limiting->cfg = NULL;
+			rlim = bevp->rate_limiting;
+			rlim->cfg = NULL;
 			bufferevent_unsuspend_read(bev, BEV_SUSPEND_BW);
 			bufferevent_unsuspend_write(bev, BEV_SUSPEND_BW);
+			if (event_initialized(&rlim->refill_bucket_event))
+				event_del(&rlim->refill_bucket_event);
 		}
 		r = 0;
 		goto done;
@@ -561,29 +565,48 @@ bufferevent_set_rate_limit(struct bufferevent *bev,
 	tick = ev_token_bucket_get_tick(&now, cfg);
 
 	if (bevp->rate_limiting && bevp->rate_limiting->cfg == cfg) {
-		;
-	} else if (bevp->rate_limiting) {
-		bevp->rate_limiting->cfg = cfg;
-		ev_token_bucket_init(&bevp->rate_limiting->limit, cfg, tick, 1);
-		if (bevp->rate_limiting->limit.read_limit > 0)
-			bufferevent_unsuspend_read(bev, BEV_SUSPEND_BW);
-		else
-			bufferevent_suspend_read(bev, BEV_SUSPEND_BW);
-		if (bevp->rate_limiting->limit.write_limit > 0)
-			bufferevent_unsuspend_write(bev, BEV_SUSPEND_BW);
-		else
-			bufferevent_suspend_write(bev, BEV_SUSPEND_BW);
-	} else {
+		/* no-op */
+		r = 0;
+		goto done;
+	}
+	if (bevp->rate_limiting == NULL) {
 		rlim = mm_calloc(1, sizeof(struct bufferevent_rate_limit));
 		if (!rlim)
 			goto done;
-		rlim->cfg = cfg;
-		ev_token_bucket_init(&rlim->limit, cfg, tick, 0);
-		evtimer_assign(&rlim->refill_bucket_event, bev->ev_base,
-		    _bev_refill_callback, bevp);
 		bevp->rate_limiting = rlim;
+	} else {
+		rlim = bevp->rate_limiting;
+	}
+	reinit = rlim->cfg != NULL;
+
+	rlim->cfg = cfg;
+	ev_token_bucket_init(&rlim->limit, cfg, tick, reinit);
+
+	if (reinit) {
+		EVUTIL_ASSERT(event_initialized(&rlim->refill_bucket_event));
+		event_del(&rlim->refill_bucket_event);
 	}
+	evtimer_assign(&rlim->refill_bucket_event, bev->ev_base,
+	    _bev_refill_callback, bevp);
+
+	if (rlim->limit.read_limit > 0) {
+		bufferevent_unsuspend_read(bev, BEV_SUSPEND_BW);
+	} else {
+		bufferevent_suspend_read(bev, BEV_SUSPEND_BW);
+		suspended=1;
+	}
+	if (rlim->limit.write_limit > 0) {
+		bufferevent_unsuspend_write(bev, BEV_SUSPEND_BW);
+	} else {
+		bufferevent_suspend_write(bev, BEV_SUSPEND_BW);
+		suspended = 1;
+	}
+
+	if (suspended)
+		event_add(&rlim->refill_bucket_event, &cfg->tick_timeout);
+
 	r = 0;
+
 done:
 	BEV_UNLOCK(bev);
 	return r;
@@ -856,7 +879,8 @@ bufferevent_decrement_read_limit(struct bufferevent *bev, ev_ssize_t decr)
 			&bevp->rate_limiting->cfg->tick_timeout) < 0)
 			r = -1;
 	} else if (old_limit <= 0 && new_limit > 0) {
-		event_del(&bevp->rate_limiting->refill_bucket_event);
+		if (!(bevp->write_suspended & BEV_SUSPEND_BW))
+			event_del(&bevp->rate_limiting->refill_bucket_event);
 		bufferevent_unsuspend_read(bev, BEV_SUSPEND_BW);
 	}
 
@@ -884,7 +908,8 @@ bufferevent_decrement_write_limit(struct bufferevent *bev, ev_ssize_t decr)
 			&bevp->rate_limiting->cfg->tick_timeout) < 0)
 			r = -1;
 	} else if (old_limit <= 0 && new_limit > 0) {
-		event_del(&bevp->rate_limiting->refill_bucket_event);
+		if (!(bevp->read_suspended & BEV_SUSPEND_BW))
+			event_del(&bevp->rate_limiting->refill_bucket_event);
 		bufferevent_unsuspend_write(bev, BEV_SUSPEND_BW);
 	}