runtime: call enableMetadataHugePages and its callees on the systemstack

mknyszek · gopherbot · commit 5f08b4479930 · 2023-11-13T14:11:13.000Z
These functions acquire the heap lock. If they're not called on the systemstack, a stack growth could cause a self-deadlock since stack growth may allocate memory from the page heap. This has been a problem for a while. If this is what's plaguing the ppc64 port right now, it's very surprising (and probably just coincidental) that it's showing up now. For #64050. For #64062. Fixes #64067. Change-Id: I2b95dc134d17be63b9fe8f7a3370fe5b5438682f Reviewed-on: https://go-review.googlesource.com/c/go/+/541635 LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com> Run-TryBot: Michael Knyszek <mknyszek@google.com> Auto-Submit: Michael Knyszek <mknyszek@google.com> TryBot-Result: Gopher Robot <gobot@golang.org> Reviewed-by: Michael Pratt <mpratt@google.com> Reviewed-by: Paul Murphy <murp@ibm.com>
diff --git a/src/runtime/malloc.go b/src/runtime/malloc.go
@@ -872,6 +872,10 @@ retry:
 //
 // The heap lock must not be held over this operation, since it will briefly acquire
 // the heap lock.
+//
+// Must be called on the system stack because it acquires the heap lock.
+//
+//go:systemstack
 func (h *mheap) enableMetadataHugePages() {
 	// Enable huge pages for page structure.
 	h.pages.enableChunkHugePages()
diff --git a/src/runtime/mgc.go b/src/runtime/mgc.go
@@ -1190,7 +1190,9 @@ func gcMarkTermination() {
 
 	// Enable huge pages on some metadata if we cross a heap threshold.
 	if gcController.heapGoal() > minHeapForMetadataHugePages {
-		mheap_.enableMetadataHugePages()
+		systemstack(func() {
+			mheap_.enableMetadataHugePages()
+		})
 	}
 
 	semrelease(&worldsema)
diff --git a/src/runtime/mpagealloc.go b/src/runtime/mpagealloc.go
@@ -437,6 +437,10 @@ func (p *pageAlloc) grow(base, size uintptr) {
 //
 // The heap lock must not be held over this operation, since it will briefly acquire
 // the heap lock.
+//
+// Must be called on the system stack because it acquires the heap lock.
+//
+//go:systemstack
 func (p *pageAlloc) enableChunkHugePages() {
 	// Grab the heap lock to turn on huge pages for new chunks and clone the current
 	// heap address space ranges.

Original file line number	Diff line number	Diff line change
`@@ -1190,7 +1190,9 @@ func gcMarkTermination() {`
`1190`	`1190`
`1191`	`1191`	`// Enable huge pages on some metadata if we cross a heap threshold.`
`1192`	`1192`	`if gcController.heapGoal() > minHeapForMetadataHugePages {`
`1193`		`- mheap_.enableMetadataHugePages()`
	`1193`	`+ systemstack(func() {`
	`1194`	`+ mheap_.enableMetadataHugePages()`
	`1195`	`+ })`
`1194`	`1196`	`}`
`1195`	`1197`
`1196`	`1198`	`semrelease(&worldsema)`