Stowage/go
2
0
Fork 0
mirror of https://github.com/golang/go.git synced 2025-12-08 06:10:04 +00:00
Code Issues Projects Releases Packages Wiki Activity

runtime: ensure mheap lock stack growth invariant is maintained

Browse source 
Currently there's an invariant in the runtime wherein the heap lock
can only be acquired on the system stack, otherwise a self-deadlock
could occur if the stack grows while the lock is held.

This invariant is upheld and documented in a number of situations (e.g.
allocManual, freeManual) but there are other places where the invariant
is either not maintained at all which risks self-deadlock (e.g.
setGCPercent, gcResetMarkState, allocmcache) or is maintained but
undocumented (e.g. gcSweep, readGCStats_m).

This change adds go:systemstack to any function that acquires the heap
lock or adds a systemstack(func() { ... }) around the critical section,
where appropriate. It also documents the invariant on (*mheap).lock
directly and updates repetitive documentation to refer to that comment.

Fixes #32105.

Change-Id: I702b1290709c118b837389c78efde25c51a2cafb
Reviewed-on: https://go-review.googlesource.com/c/go/+/177857
Run-TryBot: Michael Knyszek <mknyszek@google.com>
Reviewed-by: Austin Clements <austin@google.com>
This commit is contained in:
Michael Anthony Knyszek 2019-05-17 14:48:04 +00:00 • committed by Michael Knyszek
parent db3255536c
commit 7ed7669c0d
5 changed files with 64 additions and 35 deletions
Download patch file Download diff file Expand all files Collapse all files

11
src/runtime/mheap.go
View file

@ -29,6 +29,8 @@ const minPhysPageSize = 4096
//
//go:notinheap
type mheap struct {
// lock must only be acquired on the system stack, otherwise a g
// could self-deadlock if its stack grows with the lock held.
lock mutex
free mTreap // free spans
sweepgen uint32 // sweep generation, see comment in mspan
@ -1095,9 +1097,8 @@ func (h *mheap) alloc(npage uintptr, spanclass spanClass, large bool, needzero b
// The memory backing the returned span may not be zeroed if
// span.needzero is set.
//
// allocManual must be called on the system stack to prevent stack
// growth. Since this is used by the stack allocator, stack growth
// during allocManual would self-deadlock.
// allocManual must be called on the system stack because it acquires
// the heap lock. See mheap for details.
//
//go:systemstack
func (h *mheap) allocManual(npage uintptr, stat *uint64) *mspan {
@ -1303,8 +1304,8 @@ func (h *mheap) freeSpan(s *mspan, large bool) {
// This must only be called when gcphase == _GCoff. See mSpanState for
// an explanation.
//
// freeManual must be called on the system stack to prevent stack
// growth, just like allocManual.
// freeManual must be called on the system stack because it acquires
// the heap lock. See mheap for details.
//
//go:systemstack
func (h *mheap) freeManual(s *mspan, stat *uint64) {