runtime: fix missing pprof labels

Use gp.m.curg instead of the gp when recording cpu profiler stack
traces. This ensures profiler labels are captured when systemstack or similar
is executing on behalf of the current goroutine.

After this there are still rare cases of samples containing the labelHog
function, so more work might be needed. This patch should fix ~99% of the
problem.

Also change testCPUProfile interface a little to allow the new test to
re-run with a longer duration if it fails during a -short run.

Fixes #48577.

Change-Id: I3dbc9fd5af3c513544e822acaa43055b2e00dfa9
Reviewed-on: https://go-review.googlesource.com/c/go/+/367200
Trust: Michael Pratt <mpratt@google.com>
Trust: Bryan Mills <bcmills@google.com>
Run-TryBot: Michael Pratt <mpratt@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Michael Pratt <mpratt@google.com>

1 files changed, 8 insertions, 1 deletions

diff --git a/src/runtime/proc.go b/src/runtime/proc.go
index f375b67981..7509f7632f 100644
--- a/src/runtime/proc.go
+++ b/src/runtime/proc.go
@@ -4726,7 +4726,14 @@ func sigprof(pc, sp, lr uintptr, gp *g, mp *m) {
 	}
 
 	if prof.hz != 0 {
-		cpuprof.add(gp, stk[:n])
+		// Note: it can happen on Windows that we interrupted a system thread
+		// with no g, so gp could nil. The other nil checks are done out of
+		// caution, but not expected to be nil in practice.
+		var tagPtr *unsafe.Pointer
+		if gp != nil && gp.m != nil && gp.m.curg != nil {
+			tagPtr = &gp.m.curg.labels
+		}
+		cpuprof.add(tagPtr, stk[:n])
 	}
 	getg().m.mallocing--
 }