net/textproto, sync: unlock mutexes appropriately before panics

Ensure mutexes are unlocked right before panics, where defers aren’t easily usable.

Change-Id: I67c9870e7a626f590a8de8df6c8341c5483918dc
GitHub-Last-Rev: bb8ffe5
GitHub-Pull-Request: #37143
Reviewed-on: https://go-review.googlesource.com/c/go/+/218717
Reviewed-by: Emmanuel Odeke <[email protected]>
Run-TryBot: Emmanuel Odeke <[email protected]>
TryBot-Result: Gobot Gobot <[email protected]>

Author: Chain-Fox

src/net/textproto/pipeline.go

@@ -99,6 +99,7 @@ func (s *sequencer) Start(id uint) {
 func (s *sequencer) End(id uint) {
 	s.mu.Lock()
 	if s.id != id {
+		s.mu.Unlock()
 		panic("out of sync")
 	}
 	id++

src/sync/rwmutex_test.go

@@ -59,6 +59,7 @@ func reader(rwm *RWMutex, num_iterations int, activity *int32, cdone chan bool)
 		rwm.RLock()
 		n := atomic.AddInt32(activity, 1)
 		if n < 1 || n >= 10000 {
+			rwm.RUnlock()
 			panic(fmt.Sprintf("wlock(%d)\n", n))
 		}
 		for i := 0; i < 100; i++ {
@@ -74,6 +75,7 @@ func writer(rwm *RWMutex, num_iterations int, activity *int32, cdone chan bool)
 		rwm.Lock()
 		n := atomic.AddInt32(activity, 10000)
 		if n != 10000 {
+			rwm.Unlock()
 			panic(fmt.Sprintf("wlock(%d)\n", n))
 		}
 		for i := 0; i < 100; i++ {