runtime: add heap lock assertions

Some functions that required holding the heap lock _or_ world stop have
been simplified to simply requiring the heap lock. This is conceptually
simpler and taking the heap lock during world stop is guaranteed to not
contend. This was only done on functions already called on the
systemstack to avoid too many extra systemstack calls in GC.

Updates #40677

Change-Id: I15aa1dadcdd1a81aac3d2a9ecad6e7d0377befdc
Reviewed-on: https://go-review.googlesource.com/c/go/+/250262
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>

src/runtime/export_test.go

@@ -743,7 +743,16 @@ func (c *PageCache) Alloc(npages uintptr) (uintptr, uintptr) {
 	return (*pageCache)(c).alloc(npages)
 }
 func (c *PageCache) Flush(s *PageAlloc) {
-	(*pageCache)(c).flush((*pageAlloc)(s))
+	cp := (*pageCache)(c)
+	sp := (*pageAlloc)(s)
+
+	systemstack(func() {
+		// None of the tests need any higher-level locking, so we just
+		// take the lock internally.
+		lock(sp.mheapLock)
+		cp.flush(sp)
+		unlock(sp.mheapLock)
+	})
 }
 
 // Expose chunk index type.
@@ -754,20 +763,50 @@ type ChunkIdx chunkIdx
 type PageAlloc pageAlloc
 
 func (p *PageAlloc) Alloc(npages uintptr) (uintptr, uintptr) {
-	return (*pageAlloc)(p).alloc(npages)
+	pp := (*pageAlloc)(p)
+
+	var addr, scav uintptr
+	systemstack(func() {
+		// None of the tests need any higher-level locking, so we just
+		// take the lock internally.
+		lock(pp.mheapLock)
+		addr, scav = pp.alloc(npages)
+		unlock(pp.mheapLock)
+	})
+	return addr, scav
 }
 func (p *PageAlloc) AllocToCache() PageCache {
-	return PageCache((*pageAlloc)(p).allocToCache())
+	pp := (*pageAlloc)(p)
+
+	var c PageCache
+	systemstack(func() {
+		// None of the tests need any higher-level locking, so we just
+		// take the lock internally.
+		lock(pp.mheapLock)
+		c = PageCache(pp.allocToCache())
+		unlock(pp.mheapLock)
+	})
+	return c
 }
 func (p *PageAlloc) Free(base, npages uintptr) {
-	(*pageAlloc)(p).free(base, npages)
+	pp := (*pageAlloc)(p)
+
+	systemstack(func() {
+		// None of the tests need any higher-level locking, so we just
+		// take the lock internally.
+		lock(pp.mheapLock)
+		pp.free(base, npages)
+		unlock(pp.mheapLock)
+	})
 }
 func (p *PageAlloc) Bounds() (ChunkIdx, ChunkIdx) {
 	return ChunkIdx((*pageAlloc)(p).start), ChunkIdx((*pageAlloc)(p).end)
 }
 func (p *PageAlloc) Scavenge(nbytes uintptr, mayUnlock bool) (r uintptr) {
 	pp := (*pageAlloc)(p)
 	systemstack(func() {
+		// None of the tests need any higher-level locking, so we just
+		// take the lock internally.
 		lock(pp.mheapLock)
 		r = pp.scavenge(nbytes, mayUnlock)
 		unlock(pp.mheapLock)
@@ -926,7 +965,11 @@ func NewPageAlloc(chunks, scav map[ChunkIdx][]BitRange) *PageAlloc {
 		addr := chunkBase(chunkIdx(i))
 
 		// Mark the chunk's existence in the pageAlloc.
-		p.grow(addr, pallocChunkBytes)
+		systemstack(func() {
+			lock(p.mheapLock)
+			p.grow(addr, pallocChunkBytes)
+			unlock(p.mheapLock)
+		})
 
 		// Initialize the bitmap and update pageAlloc metadata.
 		chunk := p.chunkOf(chunkIndex(addr))
@@ -957,13 +1000,19 @@ func NewPageAlloc(chunks, scav map[ChunkIdx][]BitRange) *PageAlloc {
 		}
 
 		// Update heap metadata for the allocRange calls above.
-		p.update(addr, pallocChunkPages, false, false)
+		systemstack(func() {
+			lock(p.mheapLock)
+			p.update(addr, pallocChunkPages, false, false)
+			unlock(p.mheapLock)
+		})
 	}
+
 	systemstack(func() {
 		lock(p.mheapLock)
 		p.scavengeStartGen()
 		unlock(p.mheapLock)
 	})
+
 	return (*PageAlloc)(p)
 }
 

src/runtime/malloc.go

@@ -627,6 +627,8 @@ func mallocinit() {
 //
 // h must be locked.
 func (h *mheap) sysAlloc(n uintptr) (v unsafe.Pointer, size uintptr) {
+	assertLockHeld(&h.lock)
+
 	n = alignUp(n, heapArenaBytes)
 
 	// First, try the arena pre-reservation.

src/runtime/mgc.go

@@ -821,6 +821,8 @@ func pollFractionalWorkerExit() bool {
 //
 // mheap_.lock must be held or the world must be stopped.
 func gcSetTriggerRatio(triggerRatio float64) {
+	assertWorldStoppedOrLockHeld(&mheap_.lock)
+
 	// Compute the next GC goal, which is when the allocated heap
 	// has grown by GOGC/100 over the heap marked by the last
 	// cycle.
@@ -960,6 +962,8 @@ func gcSetTriggerRatio(triggerRatio float64) {
 //
 // mheap_.lock must be held or the world must be stopped.
 func gcEffectiveGrowthRatio() float64 {
+	assertWorldStoppedOrLockHeld(&mheap_.lock)
+
 	egogc := float64(atomic.Load64(&memstats.next_gc)-memstats.heap_marked) / float64(memstats.heap_marked)
 	if egogc < 0 {
 		// Shouldn't happen, but just in case.

src/runtime/mgcscavenge.go

@@ -397,6 +397,8 @@ func bgscavenge(c chan int) {
 //
 //go:systemstack
 func (p *pageAlloc) scavenge(nbytes uintptr, mayUnlock bool) uintptr {
+	assertLockHeld(p.mheapLock)
+
 	var (
 		addrs addrRange
 		gen   uint32
@@ -446,6 +448,8 @@ func printScavTrace(gen uint32, released uintptr, forced bool) {
 //
 //go:systemstack
 func (p *pageAlloc) scavengeStartGen() {
+	assertLockHeld(p.mheapLock)
+
 	if debug.scavtrace > 0 {
 		printScavTrace(p.scav.gen, p.scav.released, false)
 	}
@@ -495,6 +499,8 @@ func (p *pageAlloc) scavengeStartGen() {
 //
 //go:systemstack
 func (p *pageAlloc) scavengeReserve() (addrRange, uint32) {
+	assertLockHeld(p.mheapLock)
+
 	// Start by reserving the minimum.
 	r := p.scav.inUse.removeLast(p.scav.reservationBytes)
 
@@ -525,6 +531,8 @@ func (p *pageAlloc) scavengeReserve() (addrRange, uint32) {
 //
 //go:systemstack
 func (p *pageAlloc) scavengeUnreserve(r addrRange, gen uint32) {
+	assertLockHeld(p.mheapLock)
+
 	if r.size() == 0 || gen != p.scav.gen {
 		return
 	}
@@ -552,6 +560,8 @@ func (p *pageAlloc) scavengeUnreserve(r addrRange, gen uint32) {
 //
 //go:systemstack
 func (p *pageAlloc) scavengeOne(work addrRange, max uintptr, mayUnlock bool) (uintptr, addrRange) {
+	assertLockHeld(p.mheapLock)
+
 	// Defensively check if we've recieved an empty address range.
 	// If so, just return.
 	if work.size() == 0 {
@@ -610,6 +620,8 @@ func (p *pageAlloc) scavengeOne(work addrRange, max uintptr, mayUnlock bool) (ui
 		// If we found something, scavenge it and return!
 		if npages != 0 {
 			work.limit = offAddr{p.scavengeRangeLocked(maxChunk, base, npages)}
+
+			assertLockHeld(p.mheapLock) // Must be locked on return.
 			return uintptr(npages) * pageSize, work
 		}
 	}
@@ -674,12 +686,16 @@ func (p *pageAlloc) scavengeOne(work addrRange, max uintptr, mayUnlock bool) (ui
 		base, npages := chunk.findScavengeCandidate(pallocChunkPages-1, minPages, maxPages)
 		if npages > 0 {
 			work.limit = offAddr{p.scavengeRangeLocked(candidateChunkIdx, base, npages)}
+
+			assertLockHeld(p.mheapLock) // Must be locked on return.
 			return uintptr(npages) * pageSize, work
 		}
 
 		// We were fooled, so let's continue from where we left off.
 		work.limit = offAddr{chunkBase(candidateChunkIdx)}
 	}
+
+	assertLockHeld(p.mheapLock) // Must be locked on return.
 	return 0, work
 }
 
@@ -692,6 +708,8 @@ func (p *pageAlloc) scavengeOne(work addrRange, max uintptr, mayUnlock bool) (ui
 //
 // p.mheapLock must be held.
 func (p *pageAlloc) scavengeRangeLocked(ci chunkIdx, base, npages uint) uintptr {
+	assertLockHeld(p.mheapLock)
+
 	p.chunkOf(ci).scavenged.setRange(base, npages)
 
 	// Compute the full address for the start of the range.

src/runtime/mheap.go

@@ -483,10 +483,15 @@ func (s *mspan) layout() (size, n, total uintptr) {
 // indirect call from the fixalloc initializer, the compiler can't see
 // this.
 //
+// The heap lock must be held.
+//
 //go:nowritebarrierrec
 func recordspan(vh unsafe.Pointer, p unsafe.Pointer) {
 	h := (*mheap)(vh)
 	s := (*mspan)(p)
+
+	assertLockHeld(&h.lock)
+
 	if len(h.allspans) >= cap(h.allspans) {
 		n := 64 * 1024 / sys.PtrSize
 		if n < cap(h.allspans)*3/2 {
@@ -721,7 +726,7 @@ func (h *mheap) init() {
 //
 // reclaim implements the page-reclaimer half of the sweeper.
 //
-// h must NOT be locked.
+// h.lock must NOT be held.
 func (h *mheap) reclaim(npage uintptr) {
 	// TODO(austin): Half of the time spent freeing spans is in
 	// locking/unlocking the heap (even with low contention). We
@@ -804,6 +809,8 @@ func (h *mheap) reclaimChunk(arenas []arenaIdx, pageIdx, n uintptr) uintptr {
 	// In particular, if a span were freed and merged concurrently
 	// with this probing heapArena.spans, it would be possible to
 	// observe arbitrary, stale span pointers.
+	assertLockHeld(&h.lock)
+
 	n0 := n
 	var nFreed uintptr
 	sg := h.sweepgen
@@ -858,6 +865,8 @@ func (h *mheap) reclaimChunk(arenas []arenaIdx, pageIdx, n uintptr) uintptr {
 		traceGCSweepSpan((n0 - nFreed) * pageSize)
 		lock(&h.lock)
 	}
+
+	assertLockHeld(&h.lock) // Must be locked on return.
 	return nFreed
 }
 
@@ -1011,7 +1020,7 @@ func (h *mheap) allocNeedsZero(base, npage uintptr) (needZero bool) {
 // tryAllocMSpan attempts to allocate an mspan object from
 // the P-local cache, but may fail.
 //
-// h need not be locked.
+// h.lock need not be held.
 //
 // This caller must ensure that its P won't change underneath
 // it during this function. Currently to ensure that we enforce
@@ -1035,7 +1044,7 @@ func (h *mheap) tryAllocMSpan() *mspan {
 
 // allocMSpanLocked allocates an mspan object.
 //
-// h must be locked.
+// h.lock must be held.
 //
 // allocMSpanLocked must be called on the system stack because
 // its caller holds the heap lock. See mheap for details.
@@ -1044,6 +1053,8 @@ func (h *mheap) tryAllocMSpan() *mspan {
 //
 //go:systemstack
 func (h *mheap) allocMSpanLocked() *mspan {
+	assertLockHeld(&h.lock)
+
 	pp := getg().m.p.ptr()
 	if pp == nil {
 		// We don't have a p so just do the normal thing.
@@ -1065,7 +1076,7 @@ func (h *mheap) allocMSpanLocked() *mspan {
 
 // freeMSpanLocked free an mspan object.
 //
-// h must be locked.
+// h.lock must be held.
 //
 // freeMSpanLocked must be called on the system stack because
 // its caller holds the heap lock. See mheap for details.
@@ -1074,6 +1085,8 @@ func (h *mheap) allocMSpanLocked() *mspan {
 //
 //go:systemstack
 func (h *mheap) freeMSpanLocked(s *mspan) {
+	assertLockHeld(&h.lock)
+
 	pp := getg().m.p.ptr()
 	// First try to free the mspan directly to the cache.
 	if pp != nil && pp.mspancache.len < len(pp.mspancache.buf) {
@@ -1097,7 +1110,7 @@ func (h *mheap) freeMSpanLocked(s *mspan) {
 //
 // The returned span is fully initialized.
 //
-// h must not be locked.
+// h.lock must not be held.
 //
 // allocSpan must be called on the system stack both because it acquires
 // the heap lock and because it must block GC transitions.
@@ -1281,8 +1294,10 @@ HaveSpan:
 // Try to add at least npage pages of memory to the heap,
 // returning whether it worked.
 //
-// h must be locked.
+// h.lock must be held.
 func (h *mheap) grow(npage uintptr) bool {
+	assertLockHeld(&h.lock)
+
 	// We must grow the heap in whole palloc chunks.
 	ask := alignUp(npage, pallocChunkPages) * pageSize
 
@@ -1391,6 +1406,8 @@ func (h *mheap) freeManual(s *mspan, typ spanAllocType) {
 }
 
 func (h *mheap) freeSpanLocked(s *mspan, typ spanAllocType) {
+	assertLockHeld(&h.lock)
+
 	switch s.state.get() {
 	case mSpanManual:
 		if s.allocCount != 0 {