runtime: run mutexevent profiling without holding semaRoot lock

Suggested by Dmitry in CL 36792 review.
Clearly safe since there are many different semaRoots
that could all have profiled sudogs calling mutexevent.

Change-Id: I45eed47a5be3e513b2dad63b60afcd94800e16d1
Reviewed-on: https://go-review.googlesource.com/37104
Run-TryBot: Russ Cox <rsc@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Dmitry Vyukov <dvyukov@google.com>

diff --git a/src/runtime/sema.go b/src/runtime/sema.go
index 5b9a264ebd93272ddb570dd3229d657e4f4805cd..9d4cc3c036e5f4b1f0c31218223dfca2ec6a8b61 100644 (file)
--- a/src/runtime/sema.go
+++ b/src/runtime/sema.go
@@ -174,13 +174,14 @@ func semrelease(addr *uint32) {
        s, t0 := root.dequeue(addr)
        if s != nil {
                atomic.Xadd(&root.nwait, -1)
-               if s.acquiretime != 0 {
-                       mutexevent(t0-s.acquiretime, 3)
-               }
        }
        unlock(&root.lock)
        if s != nil { // May be slow, so unlock first
+               acquiretime := s.acquiretime
                readyWithTime(s, 5)
+               if acquiretime != 0 {
+                       mutexevent(t0-acquiretime, 3)
+               }
        }
 }