Revert "runtime: convert g.waitreason from string to uint8"

This reverts commit 4eea887fd477368653f6fcf8ad766030167936e5.

Reason for revert: broke s390x build

Change-Id: Id6c2b6a7319273c4d21f613d4cdd38b00d49f847
Reviewed-on: https://go-review.googlesource.com/100375
Reviewed-by: Josh Bleecher Snyder <josharian@gmail.com>

15 files changed, 47 insertions, 114 deletions

diff --git a/src/runtime/chan.go b/src/runtime/chan.go
index ce71cee4c5..10ee97d924 100644
--- a/src/runtime/chan.go
+++ b/src/runtime/chan.go
@@ -142,7 +142,7 @@ func chansend(c *hchan, ep unsafe.Pointer, block bool, callerpc uintptr) bool {
 		if !block {
 			return false
 		}
-		gopark(nil, nil, waitReasonChanSendNilChan, traceEvGoStop, 2)
+		gopark(nil, nil, "chan send (nil chan)", traceEvGoStop, 2)
 		throw("unreachable")
 	}
 
@@ -231,7 +231,7 @@ func chansend(c *hchan, ep unsafe.Pointer, block bool, callerpc uintptr) bool {
 	gp.waiting = mysg
 	gp.param = nil
 	c.sendq.enqueue(mysg)
-	goparkunlock(&c.lock, waitReasonChanSend, traceEvGoBlockSend, 3)
+	goparkunlock(&c.lock, "chan send", traceEvGoBlockSend, 3)
 
 	// someone woke us up.
 	if mysg != gp.waiting {
@@ -426,7 +426,7 @@ func chanrecv(c *hchan, ep unsafe.Pointer, block bool) (selected, received bool)
 		if !block {
 			return
 		}
-		gopark(nil, nil, waitReasonChanReceiveNilChan, traceEvGoStop, 2)
+		gopark(nil, nil, "chan receive (nil chan)", traceEvGoStop, 2)
 		throw("unreachable")
 	}
 
@@ -517,7 +517,7 @@ func chanrecv(c *hchan, ep unsafe.Pointer, block bool) (selected, received bool)
 	mysg.c = c
 	gp.param = nil
 	c.recvq.enqueue(mysg)
-	goparkunlock(&c.lock, waitReasonChanReceive, traceEvGoBlockRecv, 3)
+	goparkunlock(&c.lock, "chan receive", traceEvGoBlockRecv, 3)
 
 	// someone woke us up
 	if mysg != gp.waiting {
diff --git a/src/runtime/heapdump.go b/src/runtime/heapdump.go
index 2d2734a064..b255cbbae3 100644
--- a/src/runtime/heapdump.go
+++ b/src/runtime/heapdump.go
@@ -349,7 +349,7 @@ func dumpgoroutine(gp *g) {
 	dumpbool(isSystemGoroutine(gp))
 	dumpbool(false) // isbackground
 	dumpint(uint64(gp.waitsince))
-	dumpstr(gp.waitreason.String())
+	dumpstr(gp.waitreason)
 	dumpint(uint64(uintptr(gp.sched.ctxt)))
 	dumpint(uint64(uintptr(unsafe.Pointer(gp.m))))
 	dumpint(uint64(uintptr(unsafe.Pointer(gp._defer))))
@@ -658,7 +658,7 @@ func mdump() {
 func writeheapdump_m(fd uintptr) {
 	_g_ := getg()
 	casgstatus(_g_.m.curg, _Grunning, _Gwaiting)
-	_g_.waitreason = waitReasonDumpingHeap
+	_g_.waitreason = "dumping heap"
 
 	// Update stats so we can dump them.
 	// As a side effect, flushes all the MCaches so the MSpan.freelist
diff --git a/src/runtime/mfinal.go b/src/runtime/mfinal.go
index 6ce0312712..4ded18a345 100644
--- a/src/runtime/mfinal.go
+++ b/src/runtime/mfinal.go
@@ -172,7 +172,7 @@ func runfinq() {
 			gp := getg()
 			fing = gp
 			fingwait = true
-			goparkunlock(&finlock, waitReasonFinalizerWait, traceEvGoBlock, 1)
+			goparkunlock(&finlock, "finalizer wait", traceEvGoBlock, 1)
 			continue
 		}
 		unlock(&finlock)
diff --git a/src/runtime/mgc.go b/src/runtime/mgc.go
index f40bdbd278..ab90c289a5 100644
--- a/src/runtime/mgc.go
+++ b/src/runtime/mgc.go
@@ -241,7 +241,7 @@ func setGCPercent(in int32) (out int32) {
 			gp := getg()
 			gp.schedlink = work.sweepWaiters.head
 			work.sweepWaiters.head.set(gp)
-			goparkunlock(&work.sweepWaiters.lock, waitReasonWaitForGCCycle, traceEvGoBlock, 1)
+			goparkunlock(&work.sweepWaiters.lock, "wait for GC cycle", traceEvGoBlock, 1)
 		} else {
 			// GC isn't active.
 			unlock(&work.sweepWaiters.lock)
@@ -1100,7 +1100,7 @@ func GC() {
 		// termination of cycle N complete.
 		gp.schedlink = work.sweepWaiters.head
 		work.sweepWaiters.head.set(gp)
-		goparkunlock(&work.sweepWaiters.lock, waitReasonWaitForGCCycle, traceEvGoBlock, 1)
+		goparkunlock(&work.sweepWaiters.lock, "wait for GC cycle", traceEvGoBlock, 1)
 	} else {
 		// We're in sweep N already.
 		unlock(&work.sweepWaiters.lock)
@@ -1116,7 +1116,7 @@ func GC() {
 	if gcphase == _GCmark && atomic.Load(&work.cycles) == n+1 {
 		gp.schedlink = work.sweepWaiters.head
 		work.sweepWaiters.head.set(gp)
-		goparkunlock(&work.sweepWaiters.lock, waitReasonWaitForGCCycle, traceEvGoBlock, 1)
+		goparkunlock(&work.sweepWaiters.lock, "wait for GC cycle", traceEvGoBlock, 1)
 	} else {
 		unlock(&work.sweepWaiters.lock)
 	}
@@ -1530,7 +1530,7 @@ func gcMarkTermination(nextTriggerRatio float64) {
 	_g_.m.traceback = 2
 	gp := _g_.m.curg
 	casgstatus(gp, _Grunning, _Gwaiting)
-	gp.waitreason = waitReasonGarbageCollection
+	gp.waitreason = "garbage collection"
 
 	// Run gc on the g0 stack. We do this so that the g stack
 	// we're currently running on will no longer change. Cuts
@@ -1799,7 +1799,7 @@ func gcBgMarkWorker(_p_ *p) {
 				}
 			}
 			return true
-		}, unsafe.Pointer(park), waitReasonGCWorkerIdle, traceEvGoBlock, 0)
+		}, unsafe.Pointer(park), "GC worker (idle)", traceEvGoBlock, 0)
 
 		// Loop until the P dies and disassociates this
 		// worker (the P may later be reused, in which case
diff --git a/src/runtime/mgcmark.go b/src/runtime/mgcmark.go
index 06a2853741..270fa6cd32 100644
--- a/src/runtime/mgcmark.go
+++ b/src/runtime/mgcmark.go
@@ -251,7 +251,7 @@ func markroot(gcw *gcWork, i uint32) {
 			selfScan := gp == userG && readgstatus(userG) == _Grunning
 			if selfScan {
 				casgstatus(userG, _Grunning, _Gwaiting)
-				userG.waitreason = waitReasonGarbageCollectionScan
+				userG.waitreason = "garbage collection scan"
 			}
 
 			// TODO: scang blocks until gp's stack has
@@ -549,7 +549,7 @@ func gcAssistAlloc1(gp *g, scanWork int64) {
 
 	// gcDrainN requires the caller to be preemptible.
 	casgstatus(gp, _Grunning, _Gwaiting)
-	gp.waitreason = waitReasonGCAssistMarking
+	gp.waitreason = "GC assist marking"
 
 	// drain own cached work first in the hopes that it
 	// will be more cache friendly.
@@ -648,7 +648,7 @@ func gcParkAssist() bool {
 		return false
 	}
 	// Park.
-	goparkunlock(&work.assistQueue.lock, waitReasonGCAssistWait, traceEvGoBlockGC, 2)
+	goparkunlock(&work.assistQueue.lock, "GC assist wait", traceEvGoBlockGC, 2)
 	return true
 }
 
diff --git a/src/runtime/mgcsweep.go b/src/runtime/mgcsweep.go
index c7baa455fe..1bb19ec689 100644
--- a/src/runtime/mgcsweep.go
+++ b/src/runtime/mgcsweep.go
@@ -49,7 +49,7 @@ func bgsweep(c chan int) {
 	lock(&sweep.lock)
 	sweep.parked = true
 	c <- 1
-	goparkunlock(&sweep.lock, waitReasonGCSweepWait, traceEvGoBlock, 1)
+	goparkunlock(&sweep.lock, "GC sweep wait", traceEvGoBlock, 1)
 
 	for {
 		for gosweepone() != ^uintptr(0) {
@@ -68,7 +68,7 @@ func bgsweep(c chan int) {
 			continue
 		}
 		sweep.parked = true
-		goparkunlock(&sweep.lock, waitReasonGCSweepWait, traceEvGoBlock, 1)
+		goparkunlock(&sweep.lock, "GC sweep wait", traceEvGoBlock, 1)
 	}
 }
 
diff --git a/src/runtime/netpoll.go b/src/runtime/netpoll.go
index efcd2b855c..8dd4fb6319 100644
--- a/src/runtime/netpoll.go
+++ b/src/runtime/netpoll.go
@@ -363,7 +363,7 @@ func netpollblock(pd *pollDesc, mode int32, waitio bool) bool {
 	// this is necessary because runtime_pollUnblock/runtime_pollSetDeadline/deadlineimpl
 	// do the opposite: store to closing/rd/wd, membarrier, load of rg/wg
 	if waitio || netpollcheckerr(pd, mode) == 0 {
-		gopark(netpollblockcommit, unsafe.Pointer(gpp), waitReasonIOWait, traceEvGoBlockNet, 5)
+		gopark(netpollblockcommit, unsafe.Pointer(gpp), "IO wait", traceEvGoBlockNet, 5)
 	}
 	// be careful to not lose concurrent READY notification
 	old := atomic.Xchguintptr(gpp, 0)
diff --git a/src/runtime/proc.go b/src/runtime/proc.go
index 3efb0bd8c2..008bd244e0 100644
--- a/src/runtime/proc.go
+++ b/src/runtime/proc.go
@@ -214,7 +214,7 @@ func main() {
 		}
 	}
 	if atomic.Load(&panicking) != 0 {
-		gopark(nil, nil, waitReasonPanicWait, traceEvGoStop, 1)
+		gopark(nil, nil, "panicwait", traceEvGoStop, 1)
 	}
 
 	exit(0)
@@ -245,7 +245,7 @@ func forcegchelper() {
 			throw("forcegc: phase error")
 		}
 		atomic.Store(&forcegc.idle, 1)
-		goparkunlock(&forcegc.lock, waitReasonForceGGIdle, traceEvGoBlock, 1)
+		goparkunlock(&forcegc.lock, "force gc (idle)", traceEvGoBlock, 1)
 		// this goroutine is explicitly resumed by sysmon
 		if debug.gctrace > 0 {
 			println("GC forced")
@@ -274,11 +274,7 @@ func goschedguarded() {
 // If unlockf returns false, the goroutine is resumed.
 // unlockf must not access this G's stack, as it may be moved between
 // the call to gopark and the call to unlockf.
-// Reason explains why the goroutine has been parked.
-// It is displayed in stack traces and heap dumps.
-// Reasons should be unique and descriptive.
-// Do not re-use reasons, add new ones.
-func gopark(unlockf func(*g, unsafe.Pointer) bool, lock unsafe.Pointer, reason waitReason, traceEv byte, traceskip int) {
+func gopark(unlockf func(*g, unsafe.Pointer) bool, lock unsafe.Pointer, reason string, traceEv byte, traceskip int) {
 	mp := acquirem()
 	gp := mp.curg
 	status := readgstatus(gp)
@@ -297,7 +293,7 @@ func gopark(unlockf func(*g, unsafe.Pointer) bool, lock unsafe.Pointer, reason w
 
 // Puts the current goroutine into a waiting state and unlocks the lock.
 // The goroutine can be made runnable again by calling goready(gp).
-func goparkunlock(lock *mutex, reason waitReason, traceEv byte, traceskip int) {
+func goparkunlock(lock *mutex, reason string, traceEv byte, traceskip int) {
 	gopark(parkunlock_c, unsafe.Pointer(lock), reason, traceEv, traceskip)
 }
 
@@ -2671,7 +2667,7 @@ func goexit0(gp *g) {
 	gp._defer = nil // should be true already but just in case.
 	gp._panic = nil // non-nil for Goexit during panic. points at stack-allocated data.
 	gp.writebuf = nil
-	gp.waitreason = 0
+	gp.waitreason = ""
 	gp.param = nil
 	gp.labels = nil
 	gp.timer = nil
@@ -4497,7 +4493,7 @@ func schedtrace(detailed bool) {
 		if lockedm != nil {
 			id2 = lockedm.id
 		}
-		print("  G", gp.goid, ": status=", readgstatus(gp), "(", gp.waitreason.String(), ") m=", id1, " lockedm=", id2, "\n")
+		print("  G", gp.goid, ": status=", readgstatus(gp), "(", gp.waitreason, ") m=", id1, " lockedm=", id2, "\n")
 	}
 	unlock(&allglock)
 	unlock(&sched.lock)
diff --git a/src/runtime/runtime2.go b/src/runtime/runtime2.go
index 42def4a826..e6808ac023 100644
--- a/src/runtime/runtime2.go
+++ b/src/runtime/runtime2.go
@@ -358,20 +358,20 @@ type g struct {
 	atomicstatus   uint32
 	stackLock      uint32 // sigprof/scang lock; TODO: fold in to atomicstatus
 	goid           int64
+	waitsince      int64  // approx time when the g become blocked
+	waitreason     string // if status==Gwaiting
 	schedlink      guintptr
-	waitsince      int64      // approx time when the g become blocked
-	waitreason     waitReason // if status==Gwaiting
-	preempt        bool       // preemption signal, duplicates stackguard0 = stackpreempt
-	paniconfault   bool       // panic (instead of crash) on unexpected fault address
-	preemptscan    bool       // preempted g does scan for gc
-	gcscandone     bool       // g has scanned stack; protected by _Gscan bit in status
-	gcscanvalid    bool       // false at start of gc cycle, true if G has not run since last scan; TODO: remove?
-	throwsplit     bool       // must not split stack
-	raceignore     int8       // ignore race detection events
-	sysblocktraced bool       // StartTrace has emitted EvGoInSyscall about this goroutine
-	sysexitticks   int64      // cputicks when syscall has returned (for tracing)
-	traceseq       uint64     // trace event sequencer
-	tracelastp     puintptr   // last P emitted an event for this goroutine
+	preempt        bool     // preemption signal, duplicates stackguard0 = stackpreempt
+	paniconfault   bool     // panic (instead of crash) on unexpected fault address
+	preemptscan    bool     // preempted g does scan for gc
+	gcscandone     bool     // g has scanned stack; protected by _Gscan bit in status
+	gcscanvalid    bool     // false at start of gc cycle, true if G has not run since last scan; TODO: remove?
+	throwsplit     bool     // must not split stack
+	raceignore     int8     // ignore race detection events
+	sysblocktraced bool     // StartTrace has emitted EvGoInSyscall about this goroutine
+	sysexitticks   int64    // cputicks when syscall has returned (for tracing)
+	traceseq       uint64   // trace event sequencer
+	tracelastp     puintptr // last P emitted an event for this goroutine
 	lockedm        muintptr
 	sig            uint32
 	writebuf       []byte
@@ -752,69 +752,6 @@ const (
 // The maximum number of frames we print for a traceback
 const _TracebackMaxFrames = 100
 
-// A waitReason explains why a goroutine has been stopped.
-// See gopark. Do not re-use waitReasons, add new ones.
-type waitReason uint8
-
-const (
-	waitReasonZero                  waitReason = iota // ""
-	waitReasonGCAssistMarking                         // "GC assist marking"
-	waitReasonIOWait                                  // "IO wait"
-	waitReasonChanReceiveNilChan                      // "chan receive (nil chan)"
-	waitReasonChanSendNilChan                         // "chan send (nil chan)"
-	waitReasonDumpingHeap                             // "dumping heap"
-	waitReasonGarbageCollection                       // "garbage collection"
-	waitReasonGarbageCollectionScan                   // "garbage collection scan"
-	waitReasonPanicWait                               // "panicwait"
-	waitReasonSelect                                  // "select"
-	waitReasonSelectNoCases                           // "select (no cases)"
-	waitReasonGCAssistWait                            // "GC assist wait"
-	waitReasonGCSweepWait                             // "GC sweep wait"
-	waitReasonChanReceive                             // "chan receive"
-	waitReasonChanSend                                // "chan send"
-	waitReasonFinalizerWait                           // "finalizer wait"
-	waitReasonForceGGIdle                             // "force gc (idle)"
-	waitReasonSemacquire                              // "semacquire"
-	waitReasonSleep                                   // "sleep"
-	waitReasonTimerGoroutineIdle                      // "timer goroutine (idle)"
-	waitReasonTraceReaderBlocked                      // "trace reader (blocked)"
-	waitReasonWaitForGCCycle                          // "wait for GC cycle"
-	waitReasonGCWorkerIdle                            // "GC worker (idle)"
-)
-
-var waitReasonStrings = [...]string{
-	waitReasonZero:                  "",
-	waitReasonGCAssistMarking:       "GC assist marking",
-	waitReasonIOWait:                "IO wait",
-	waitReasonChanReceiveNilChan:    "chan receive (nil chan)",
-	waitReasonChanSendNilChan:       "chan send (nil chan)",
-	waitReasonDumpingHeap:           "dumping heap",
-	waitReasonGarbageCollection:     "garbage collection",
-	waitReasonGarbageCollectionScan: "garbage collection scan",
-	waitReasonPanicWait:             "panicwait",
-	waitReasonSelect:                "select",
-	waitReasonSelectNoCases:         "select (no cases)",
-	waitReasonGCAssistWait:          "GC assist wait",
-	waitReasonGCSweepWait:           "GC sweep wait",
-	waitReasonChanReceive:           "chan receive",
-	waitReasonChanSend:              "chan send",
-	waitReasonFinalizerWait:         "finalizer wait",
-	waitReasonForceGGIdle:           "force gc (idle)",
-	waitReasonSemacquire:            "semacquire",
-	waitReasonSleep:                 "sleep",
-	waitReasonTimerGoroutineIdle:    "timer goroutine (idle)",
-	waitReasonTraceReaderBlocked:    "trace reader (blocked)",
-	waitReasonWaitForGCCycle:        "wait for GC cycle",
-	waitReasonGCWorkerIdle:          "GC worker (idle)",
-}
-
-func (w waitReason) String() string {
-	if w < 0 || w >= waitReason(len(waitReasonStrings)) {
-		return "unknown wait reason"
-	}
-	return waitReasonStrings[w]
-}
-
 var (
 	allglen    uintptr
 	allm       *m
diff --git a/src/runtime/select.go b/src/runtime/select.go
index c48aee0642..b59c096928 100644
--- a/src/runtime/select.go
+++ b/src/runtime/select.go
@@ -189,7 +189,7 @@ func selparkcommit(gp *g, _ unsafe.Pointer) bool {
 }
 
 func block() {
-	gopark(nil, nil, waitReasonSelectNoCases, traceEvGoStop, 1) // forever
+	gopark(nil, nil, "select (no cases)", traceEvGoStop, 1) // forever
 }
 
 // selectgo implements the select statement.
@@ -389,7 +389,7 @@ loop:
 
 	// wait for someone to wake us up
 	gp.param = nil
-	gopark(selparkcommit, nil, waitReasonSelect, traceEvGoBlockSelect, 1)
+	gopark(selparkcommit, nil, "select", traceEvGoBlockSelect, 1)
 
 	sellock(scases, lockorder)
 
diff --git a/src/runtime/sema.go b/src/runtime/sema.go
index 7052d4f69d..d5ea14d46d 100644
--- a/src/runtime/sema.go
+++ b/src/runtime/sema.go
@@ -141,7 +141,7 @@ func semacquire1(addr *uint32, lifo bool, profile semaProfileFlags) {
 		// Any semrelease after the cansemacquire knows we're waiting
 		// (we set nwait above), so go to sleep.
 		root.queue(addr, s, lifo)
-		goparkunlock(&root.lock, waitReasonSemacquire, traceEvGoBlockSync, 4)
+		goparkunlock(&root.lock, "semacquire", traceEvGoBlockSync, 4)
 		if s.ticket != 0 || cansemacquire(addr) {
 			break
 		}
@@ -507,7 +507,7 @@ func notifyListWait(l *notifyList, t uint32) {
 		l.tail.next = s
 	}
 	l.tail = s
-	goparkunlock(&l.lock, waitReasonSemacquire, traceEvGoBlockCond, 3)
+	goparkunlock(&l.lock, "semacquire", traceEvGoBlockCond, 3)
 	if t0 != 0 {
 		blockevent(s.releasetime-t0, 2)
 	}
diff --git a/src/runtime/sizeof_test.go b/src/runtime/sizeof_test.go
index f8f4d563df..830055e2aa 100644
--- a/src/runtime/sizeof_test.go
+++ b/src/runtime/sizeof_test.go
@@ -23,7 +23,7 @@ func TestSizeof(t *testing.T) {
 		_32bit uintptr     // size on 32bit platforms
 		_64bit uintptr     // size on 64bit platforms
 	}{
-		{runtime.G{}, 212, 368}, // g, but exported for testing
+		{runtime.G{}, 216, 376}, // g, but exported for testing
 	}
 
 	for _, tt := range tests {
diff --git a/src/runtime/time.go b/src/runtime/time.go
index 4308cc0f0b..3ac60f3aec 100644
--- a/src/runtime/time.go
+++ b/src/runtime/time.go
@@ -99,7 +99,7 @@ func timeSleep(ns int64) {
 	tb := t.assignBucket()
 	lock(&tb.lock)
 	tb.addtimerLocked(t)
-	goparkunlock(&tb.lock, waitReasonSleep, traceEvGoSleep, 2)
+	goparkunlock(&tb.lock, "sleep", traceEvGoSleep, 2)
 }
 
 // startTimer adds t to the timer heap.
@@ -250,7 +250,7 @@ func timerproc(tb *timersBucket) {
 		if delta < 0 || faketime > 0 {
 			// No timers left - put goroutine to sleep.
 			tb.rescheduling = true
-			goparkunlock(&tb.lock, waitReasonTimerGoroutineIdle, traceEvGoBlock, 1)
+			goparkunlock(&tb.lock, "timer goroutine (idle)", traceEvGoBlock, 1)
 			continue
 		}
 		// At least one timer pending. Sleep until then.
diff --git a/src/runtime/trace.go b/src/runtime/trace.go
index 250f19228c..c4090ff29a 100644
--- a/src/runtime/trace.go
+++ b/src/runtime/trace.go
@@ -392,7 +392,7 @@ func ReadTrace() []byte {
 	// Wait for new data.
 	if trace.fullHead == 0 && !trace.shutdown {
 		trace.reader.set(getg())
-		goparkunlock(&trace.lock, waitReasonTraceReaderBlocked, traceEvGoBlock, 2)
+		goparkunlock(&trace.lock, "trace reader (blocked)", traceEvGoBlock, 2)
 		lock(&trace.lock)
 	}
 	// Write a buffer.
diff --git a/src/runtime/traceback.go b/src/runtime/traceback.go
index 3c572a7b28..2261942ab4 100644
--- a/src/runtime/traceback.go
+++ b/src/runtime/traceback.go
@@ -827,8 +827,8 @@ func goroutineheader(gp *g) {
 	}
 
 	// Override.
-	if gpstatus == _Gwaiting && gp.waitreason != waitReasonZero {
-		status = gp.waitreason.String()
+	if gpstatus == _Gwaiting && gp.waitreason != "" {
+		status = gp.waitreason
 	}
 
 	// approx time the G is blocked, in minutes