runtime/pprof: relax TestProfilerStackDepth

The TestProfilerStackDepth/heap test can spuriously fail if the profiler
happens to capture a stack with an allocation several frames deep into
runtime code. The pprof API hides runtime frames at the leaf-end of
stacks, but those frames still count against the profiler's stack depth
limit. The test checks only the first stack it finds with the desired
prefix and fails if it's not deep enough or doesn't have the right root
frame. So it can fail in that scenario, even though the implementation
isn't really broken.

Relax the test to check that there is at least one stack with desired
prefix, depth, and root frame.

Fixes #70112

Change-Id: I337fb3cccd1ddde76530b03aa1ec0f9608aa4112
Reviewed-on: https://go-review.googlesource.com/c/go/+/623998
Reviewed-by: Felix Geisendörfer <felix.geisendoerfer@datadoghq.com>
Reviewed-by: Michael Pratt <mpratt@google.com>
Reviewed-by: Cherry Mui <cherryyz@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>

1 files changed, 25 insertions, 10 deletions

diff --git a/src/runtime/pprof/pprof_test.go b/src/runtime/pprof/pprof_test.go
index 19641f62aa..64ca9957d2 100644
--- a/src/runtime/pprof/pprof_test.go
+++ b/src/runtime/pprof/pprof_test.go
@@ -2545,19 +2545,34 @@ func TestProfilerStackDepth(t *testing.T) {
 			t.Logf("Profile = %v", p)
 
 			stks := profileStacks(p)
-			var stk []string
-			for _, s := range stks {
-				if hasPrefix(s, test.prefix) {
-					stk = s
-					break
+			var matchedStacks [][]string
+			for _, stk := range stks {
+				if !hasPrefix(stk, test.prefix) {
+					continue
 				}
+				// We may get multiple stacks which contain the prefix we want, but
+				// which might not have enough frames, e.g. if the profiler hides
+				// some leaf frames that would count against the stack depth limit.
+				// Check for at least one match
+				matchedStacks = append(matchedStacks, stk)
+				if len(stk) != depth {
+					continue
+				}
+				if rootFn, wantFn := stk[depth-1], "runtime/pprof.produceProfileEvents"; rootFn != wantFn {
+					continue
+				}
+				// Found what we wanted
+				return
 			}
-			if len(stk) != depth {
-				t.Fatalf("want stack depth = %d, got %d", depth, len(stk))
-			}
+			for _, stk := range matchedStacks {
+				t.Logf("matched stack=%s", stk)
+				if len(stk) != depth {
+					t.Errorf("want stack depth = %d, got %d", depth, len(stk))
+				}
 
-			if rootFn, wantFn := stk[depth-1], "runtime/pprof.produceProfileEvents"; rootFn != wantFn {
-				t.Fatalf("want stack stack root %s, got %v", wantFn, rootFn)
+				if rootFn, wantFn := stk[depth-1], "runtime/pprof.produceProfileEvents"; rootFn != wantFn {
+					t.Errorf("want stack stack root %s, got %v", wantFn, rootFn)
+				}
 			}
 		})
 	}