runtime: add world-stopped assertions

Stopping the world is an implicit lock for many operations, so we should
assert the world is stopped in functions that require it.

This is enabled along with the rest of lock ranking, though it is a bit
orthogonal and likely cheap enough to enable all the time should we
choose.

Requiring a lock _or_ world stop is common, so that can be expressed as
well.

Updates #40677

Change-Id: If0a58544f4251d367f73c4120c9d39974c6cd091
Reviewed-on: https://go-review.googlesource.com/c/go/+/248577
Run-TryBot: Michael Pratt <mpratt@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Austin Clements <austin@google.com>
Trust: Michael Pratt <mpratt@google.com>

1 files changed, 11 insertions, 3 deletions

diff --git a/src/runtime/mstats.go b/src/runtime/mstats.go
index e0a417d213..3829355d7b 100644
--- a/src/runtime/mstats.go
+++ b/src/runtime/mstats.go
@@ -601,6 +601,8 @@ func readGCStats_m(pauses *[]uint64) {
 //
 //go:nowritebarrier
 func updatememstats() {
+	assertWorldStopped()
+
 	// Flush mcaches to mcentral before doing anything else.
 	//
 	// Flushing to the mcentral may in general cause stats to
@@ -706,6 +708,8 @@ func updatememstats() {
 //
 //go:nowritebarrier
 func flushmcache(i int) {
+	assertWorldStopped()
+
 	p := allp[i]
 	c := p.mcache
 	if c == nil {
@@ -721,6 +725,8 @@ func flushmcache(i int) {
 //
 //go:nowritebarrier
 func flushallmcaches() {
+	assertWorldStopped()
+
 	for i := 0; i < int(gomaxprocs); i++ {
 		flushmcache(i)
 	}
@@ -876,10 +882,10 @@ func (m *consistentHeapStats) release(c *mcache) {
 // unsafeRead aggregates the delta for this shard into out.
 //
 // Unsafe because it does so without any synchronization. The
-// only safe time to call this is if the world is stopped or
-// we're freezing the world or going down anyway (and we just
-// want _some_ estimate).
+// world must be stopped.
 func (m *consistentHeapStats) unsafeRead(out *heapStatsDelta) {
+	assertWorldStopped()
+
 	for i := range m.stats {
 		out.merge(&m.stats[i])
 	}
@@ -890,6 +896,8 @@ func (m *consistentHeapStats) unsafeRead(out *heapStatsDelta) {
 // Unsafe because the world must be stopped and values should
 // be donated elsewhere before clearing.
 func (m *consistentHeapStats) unsafeClear() {
+	assertWorldStopped()
+
 	for i := range m.stats {
 		m.stats[i] = heapStatsDelta{}
 	}