runtime: remove debugCachedWork

debugCachedWork and all of its dependent fields and code were added to
aid in debugging issue #27993. Now that the source of the problem is
known and mitigated (via the extra work check after STW in gcMarkDone),
these extra checks are no longer required and simply make the code more
difficult to follow.

Remove it all.

Updates #27993

Change-Id: I594beedd5ca61733ba9cc9eaad8f80ea92df1a0d
Reviewed-on: https://go-review.googlesource.com/c/go/+/262350
Trust: Michael Pratt <mpratt@google.com>
Run-TryBot: Michael Pratt <mpratt@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Austin Clements <austin@google.com>

1 files changed, 0 insertions, 74 deletions

diff --git a/src/runtime/mgcwork.go b/src/runtime/mgcwork.go
index 46101657d5..51e0fe9219 100644
--- a/src/runtime/mgcwork.go
+++ b/src/runtime/mgcwork.go
@@ -22,13 +22,6 @@ const (
 	workbufAlloc = 32 << 10
 )
 
-// throwOnGCWork causes any operations that add pointers to a gcWork
-// buffer to throw.
-//
-// TODO(austin): This is a temporary debugging measure for issue
-// #27993. To be removed before release.
-var throwOnGCWork bool
-
 func init() {
 	if workbufAlloc%pageSize != 0 || workbufAlloc%_WorkbufSize != 0 {
 		throw("bad workbufAlloc")
@@ -93,17 +86,6 @@ type gcWork struct {
 	// termination check. Specifically, this indicates that this
 	// gcWork may have communicated work to another gcWork.
 	flushedWork bool
-
-	// pauseGen causes put operations to spin while pauseGen ==
-	// gcWorkPauseGen if debugCachedWork is true.
-	pauseGen uint32
-
-	// putGen is the pauseGen of the last putGen.
-	putGen uint32
-
-	// pauseStack is the stack at which this P was paused if
-	// debugCachedWork is true.
-	pauseStack [16]uintptr
 }
 
 // Most of the methods of gcWork are go:nowritebarrierrec because the
@@ -122,60 +104,10 @@ func (w *gcWork) init() {
 	w.wbuf2 = wbuf2
 }
 
-func (w *gcWork) checkPut(ptr uintptr, ptrs []uintptr) {
-	if debugCachedWork {
-		alreadyFailed := w.putGen == w.pauseGen
-		w.putGen = w.pauseGen
-		if !canPreemptM(getg().m) {
-			// If we were to spin, the runtime may
-			// deadlock. Since we can't be preempted, the
-			// spin could prevent gcMarkDone from
-			// finishing the ragged barrier, which is what
-			// releases us from the spin.
-			return
-		}
-		for atomic.Load(&gcWorkPauseGen) == w.pauseGen {
-		}
-		if throwOnGCWork {
-			printlock()
-			if alreadyFailed {
-				println("runtime: checkPut already failed at this generation")
-			}
-			println("runtime: late gcWork put")
-			if ptr != 0 {
-				gcDumpObject("ptr", ptr, ^uintptr(0))
-			}
-			for _, ptr := range ptrs {
-				gcDumpObject("ptrs", ptr, ^uintptr(0))
-			}
-			println("runtime: paused at")
-			for _, pc := range w.pauseStack {
-				if pc == 0 {
-					break
-				}
-				f := findfunc(pc)
-				if f.valid() {
-					// Obviously this doesn't
-					// relate to ancestor
-					// tracebacks, but this
-					// function prints what we
-					// want.
-					printAncestorTracebackFuncInfo(f, pc)
-				} else {
-					println("\tunknown PC ", hex(pc), "\n")
-				}
-			}
-			throw("throwOnGCWork")
-		}
-	}
-}
-
 // put enqueues a pointer for the garbage collector to trace.
 // obj must point to the beginning of a heap object or an oblet.
 //go:nowritebarrierrec
 func (w *gcWork) put(obj uintptr) {
-	w.checkPut(obj, nil)
-
 	flushed := false
 	wbuf := w.wbuf1
 	// Record that this may acquire the wbufSpans or heap lock to
@@ -214,8 +146,6 @@ func (w *gcWork) put(obj uintptr) {
 // otherwise it returns false and the caller needs to call put.
 //go:nowritebarrierrec
 func (w *gcWork) putFast(obj uintptr) bool {
-	w.checkPut(obj, nil)
-
 	wbuf := w.wbuf1
 	if wbuf == nil {
 		return false
@@ -237,8 +167,6 @@ func (w *gcWork) putBatch(obj []uintptr) {
 		return
 	}
 
-	w.checkPut(0, obj)
-
 	flushed := false
 	wbuf := w.wbuf1
 	if wbuf == nil {
@@ -360,12 +288,10 @@ func (w *gcWork) balance() {
 		return
 	}
 	if wbuf := w.wbuf2; wbuf.nobj != 0 {
-		w.checkPut(0, wbuf.obj[:wbuf.nobj])
 		putfull(wbuf)
 		w.flushedWork = true
 		w.wbuf2 = getempty()
 	} else if wbuf := w.wbuf1; wbuf.nobj > 4 {
-		w.checkPut(0, wbuf.obj[:wbuf.nobj])
 		w.wbuf1 = handoff(wbuf)
 		w.flushedWork = true // handoff did putfull
 	} else {