runtime: fix crash in GoroutineProfile

It was just completely broken if you gave it the number
of records it asked for. Make it impossible for that particular
inconsistency to happen again.

Also make it exclude system goroutines, to match both
NumGoroutine and Stack.

Fixes #14046.

Change-Id: Ic238c6b89934ba7b47cccd3440dd347ed11e4c3d
Reviewed-on: https://go-review.googlesource.com/18976
Run-TryBot: Russ Cox <rsc@golang.org>
Reviewed-by: Austin Clements <austin@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>

2 files changed, 44 insertions, 20 deletions

diff --git a/src/runtime/mprof.go b/src/runtime/mprof.go
index eb7231aec2..e45bc7a770 100644
--- a/src/runtime/mprof.go
+++ b/src/runtime/mprof.go
@@ -522,34 +522,46 @@ func ThreadCreateProfile(p []StackRecord) (n int, ok bool) {
 // Most clients should use the runtime/pprof package instead
 // of calling GoroutineProfile directly.
 func GoroutineProfile(p []StackRecord) (n int, ok bool) {
+	gp := getg()
+
+	isOK := func(gp1 *g) bool {
+		// Checking isSystemGoroutine here makes GoroutineProfile
+		// consistent with both NumGoroutine and Stack.
+		return gp1 != gp && readgstatus(gp1) != _Gdead && !isSystemGoroutine(gp1)
+	}
+
+	stopTheWorld("profile")
+
+	n = 1
+	for _, gp1 := range allgs {
+		if isOK(gp1) {
+			n++
+		}
+	}
 
-	n = NumGoroutine()
 	if n <= len(p) {
-		gp := getg()
-		stopTheWorld("profile")
-
-		n = NumGoroutine()
-		if n <= len(p) {
-			ok = true
-			r := p
-			sp := getcallersp(unsafe.Pointer(&p))
-			pc := getcallerpc(unsafe.Pointer(&p))
-			systemstack(func() {
-				saveg(pc, sp, gp, &r[0])
-			})
-			r = r[1:]
-			for _, gp1 := range allgs {
-				if gp1 == gp || readgstatus(gp1) == _Gdead {
-					continue
-				}
+		ok = true
+		r := p
+
+		// Save current goroutine.
+		sp := getcallersp(unsafe.Pointer(&p))
+		pc := getcallerpc(unsafe.Pointer(&p))
+		systemstack(func() {
+			saveg(pc, sp, gp, &r[0])
+		})
+		r = r[1:]
+
+		// Save other goroutines.
+		for _, gp1 := range allgs {
+			if isOK(gp1) {
 				saveg(^uintptr(0), ^uintptr(0), gp1, &r[0])
 				r = r[1:]
 			}
 		}
-
-		startTheWorld()
 	}
 
+	startTheWorld()
+
 	return n, ok
 }
 
diff --git a/src/runtime/runtime_test.go b/src/runtime/runtime_test.go
index 664c1180c4..581f52bcb0 100644
--- a/src/runtime/runtime_test.go
+++ b/src/runtime/runtime_test.go
@@ -308,3 +308,15 @@ func TestAppendSliceGrowth(t *testing.T) {
 		}
 	}
 }
+
+func TestGoroutineProfileTrivial(t *testing.T) {
+	n1, ok := GoroutineProfile(nil) // should fail, there's at least 1 goroutine
+	if n1 < 1 || ok {
+		t.Fatalf("GoroutineProfile(nil) = %d, %v, want >0, false", n1, ok)
+	}
+
+	n2, ok := GoroutineProfile(make([]StackRecord, n1))
+	if n2 != n1 || !ok {
+		t.Fatalf("GoroutineProfile(%d) = %d, %v, want %d, true", n1, n2, ok, n1)
+	}
+}