From 3bd0b0a80dd78bacf814cbe51e427dac0fd231c3 Mon Sep 17 00:00:00 2001
From: Dmitriy Vyukov <dvyukov@google.com>
Date: Thu, 15 Aug 2013 00:20:36 +0400
Subject: [PATCH] runtime: fix SetBlockProfileRate It doughtily misses all
 possible corner cases. In particular on machines with <1GHz processors,
 SetBlockProfileRate(1) disables profiling. Fixes #6114.

R=golang-dev, bradfitz, rsc
CC=golang-dev
https://golang.org/cl/12936043
---
 src/pkg/runtime/mprof.goc | 12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

diff --git a/src/pkg/runtime/mprof.goc b/src/pkg/runtime/mprof.goc
index 6e51ef3eb1..473e6e11cf 100644
--- a/src/pkg/runtime/mprof.goc
+++ b/src/pkg/runtime/mprof.goc
@@ -295,7 +295,17 @@ int64 runtime·blockprofilerate;  // in CPU ticks
 void
 runtime·SetBlockProfileRate(intgo rate)
 {
-	runtime·atomicstore64((uint64*)&runtime·blockprofilerate, rate * runtime·tickspersecond() / (1000*1000*1000));
+	int64 r;
+
+	if(rate <= 0)
+		r = 0;  // disable profiling
+	else {
+		// convert ns to cycles, use float64 to prevent overflow during multiplication
+		r = (float64)rate*runtime·tickspersecond()/(1000*1000*1000);
+		if(r == 0)
+			r = 1;
+	}
+	runtime·atomicstore64((uint64*)&runtime·blockprofilerate, r);
 }
 
 void
-- 
2.48.1