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runtime: set G wait reason more consistently
Currently, wait reasons are set somewhat inconsistently. In a follow-up CL, we're going to want to rely on the wait reason being there for casgstatus, so the status quo isn't really going to work for that. Plus this inconsistency means there are a whole bunch of cases where we could be more specific about the G's status but aren't. So, this change adds a new function, casGToWaiting which is like casgstatus but also sets the wait reason. The goal is that by using this API it'll be harder to forget to set a wait reason (or the lack thereof will at least be explicit). This change then updates all casgstatus(gp, ..., _Gwaiting) calls to casGToWaiting(gp, ..., waitReasonX) instead. For a number of these cases, we're missing a wait reason, and it wouldn't hurt to add a wait reason for them, so this change also adds those wait reasons. For #49881. Change-Id: Ia95e06ecb74ed17bb7bb94f1a362ebfe6bec1518 Reviewed-on: https://go-review.googlesource.com/c/go/+/427617 Reviewed-by: Michael Pratt <mpratt@google.com> Run-TryBot: Michael Knyszek <mknyszek@google.com> Auto-Submit: Michael Knyszek <mknyszek@google.com> TryBot-Result: Gopher Robot <gobot@golang.org>
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@ -158,11 +158,10 @@ func debugCallWrap(dispatch uintptr) {
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gp.schedlink = 0
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// Park the calling goroutine.
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gp.waitreason = waitReasonDebugCall
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if trace.enabled {
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traceGoPark(traceEvGoBlock, 1)
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}
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casgstatus(gp, _Grunning, _Gwaiting)
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casGToWaiting(gp, _Grunning, waitReasonDebugCall)
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dropg()
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// Directly execute the new goroutine. The debug
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@ -691,8 +691,7 @@ func writeheapdump_m(fd uintptr, m *MemStats) {
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assertWorldStopped()
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gp := getg()
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casgstatus(gp.m.curg, _Grunning, _Gwaiting)
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gp.waitreason = waitReasonDumpingHeap
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casGToWaiting(gp.m.curg, _Grunning, waitReasonDumpingHeap)
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// Set dump file.
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dumpfd = fd
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@ -810,7 +810,7 @@ top:
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// Otherwise, our attempt to force all P's to a safepoint could
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// result in a deadlock as we attempt to preempt a worker that's
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// trying to preempt us (e.g. for a stack scan).
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casgstatus(gp, _Grunning, _Gwaiting)
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casGToWaiting(gp, _Grunning, waitReasonGCMarkTermination)
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forEachP(func(pp *p) {
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// Flush the write barrier buffer, since this may add
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// work to the gcWork.
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@ -931,8 +931,7 @@ func gcMarkTermination() {
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mp.preemptoff = "gcing"
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mp.traceback = 2
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curgp := mp.curg
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casgstatus(curgp, _Grunning, _Gwaiting)
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curgp.waitreason = waitReasonGarbageCollection
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casGToWaiting(curgp, _Grunning, waitReasonGarbageCollection)
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// Run gc on the g0 stack. We do this so that the g stack
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// we're currently running on will no longer change. Cuts
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@ -1332,7 +1331,7 @@ func gcBgMarkWorker() {
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// the G stack. However, stack shrinking is
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// disabled for mark workers, so it is safe to
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// read from the G stack.
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casgstatus(gp, _Grunning, _Gwaiting)
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casGToWaiting(gp, _Grunning, waitReasonGCWorkerActive)
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switch pp.gcMarkWorkerMode {
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default:
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throw("gcBgMarkWorker: unexpected gcMarkWorkerMode")
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@ -218,8 +218,7 @@ func markroot(gcw *gcWork, i uint32, flushBgCredit bool) int64 {
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userG := getg().m.curg
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selfScan := gp == userG && readgstatus(userG) == _Grunning
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if selfScan {
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casgstatus(userG, _Grunning, _Gwaiting)
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userG.waitreason = waitReasonGarbageCollectionScan
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casGToWaiting(userG, _Grunning, waitReasonGarbageCollectionScan)
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}
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// TODO: suspendG blocks (and spins) until gp
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@ -560,8 +559,7 @@ func gcAssistAlloc1(gp *g, scanWork int64) {
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}
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// gcDrainN requires the caller to be preemptible.
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casgstatus(gp, _Grunning, _Gwaiting)
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gp.waitreason = waitReasonGCAssistMarking
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casGToWaiting(gp, _Grunning, waitReasonGCAssistMarking)
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// drain own cached work first in the hopes that it
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// will be more cache friendly.
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@ -1027,6 +1027,14 @@ func casgstatus(gp *g, oldval, newval uint32) {
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}
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}
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// casGToWaiting transitions gp from old to _Gwaiting, and sets the wait reason.
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//
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// Use this over casgstatus when possible to ensure that a waitreason is set.
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func casGToWaiting(gp *g, old uint32, reason waitReason) {
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gp.waitreason = reason
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casgstatus(gp, old, _Gwaiting)
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}
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// casgstatus(gp, oldstatus, Gcopystack), assuming oldstatus is Gwaiting or Grunnable.
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// Returns old status. Cannot call casgstatus directly, because we are racing with an
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// async wakeup that might come in from netpoll. If we see Gwaiting from the readgstatus,
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@ -1066,6 +1074,7 @@ func casGFromPreempted(gp *g, old, new uint32) bool {
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if old != _Gpreempted || new != _Gwaiting {
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throw("bad g transition")
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}
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gp.waitreason = waitReasonPreempted
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return gp.atomicstatus.CompareAndSwap(_Gpreempted, _Gwaiting)
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}
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@ -1098,7 +1107,8 @@ func stopTheWorld(reason string) {
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// must have preempted all goroutines, including any attempting
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// to scan our stack, in which case, any stack shrinking will
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// have already completed by the time we exit.
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casgstatus(gp, _Grunning, _Gwaiting)
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// Don't provide a wait reason because we're still executing.
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casGToWaiting(gp, _Grunning, waitReasonStoppingTheWorld)
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stopTheWorldWithSema()
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casgstatus(gp, _Gwaiting, _Grunning)
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})
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@ -3395,6 +3405,8 @@ func park_m(gp *g) {
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traceGoPark(mp.waittraceev, mp.waittraceskip)
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}
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// N.B. Not using casGToWaiting here because the waitreason is
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// set by park_m's caller.
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casgstatus(gp, _Grunning, _Gwaiting)
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dropg()
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@ -3468,7 +3480,6 @@ func preemptPark(gp *g) {
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dumpgstatus(gp)
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throw("bad g status")
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}
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gp.waitreason = waitReasonPreempted
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if gp.asyncSafePoint {
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// Double-check that async preemption does not
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@ -3545,7 +3556,7 @@ func goexit0(gp *g) {
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gp._defer = nil // should be true already but just in case.
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gp._panic = nil // non-nil for Goexit during panic. points at stack-allocated data.
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gp.writebuf = nil
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gp.waitreason = 0
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gp.waitreason = waitReasonZero
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gp.param = nil
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gp.labels = nil
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gp.timer = nil
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@ -1060,8 +1060,11 @@ const (
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waitReasonTraceReaderBlocked // "trace reader (blocked)"
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waitReasonWaitForGCCycle // "wait for GC cycle"
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waitReasonGCWorkerIdle // "GC worker (idle)"
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waitReasonGCWorkerActive // "GC worker (active)"
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waitReasonPreempted // "preempted"
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waitReasonDebugCall // "debug call"
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waitReasonGCMarkTermination // "GC mark termination"
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waitReasonStoppingTheWorld // "stopping the world"
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)
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var waitReasonStrings = [...]string{
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@ -1092,8 +1095,11 @@ var waitReasonStrings = [...]string{
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waitReasonTraceReaderBlocked: "trace reader (blocked)",
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waitReasonWaitForGCCycle: "wait for GC cycle",
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waitReasonGCWorkerIdle: "GC worker (idle)",
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waitReasonGCWorkerActive: "GC worker (active)",
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waitReasonPreempted: "preempted",
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waitReasonDebugCall: "debug call",
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waitReasonGCMarkTermination: "GC mark termination",
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waitReasonStoppingTheWorld: "stopping the world",
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}
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func (w waitReason) String() string {
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