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runtime: make sure heapBitsBulkBarrier cannot be preempted

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Changes the torture test in #12068 from failing about 1/10 times
to not failing in almost 2,000 runs.

This was only happening in -race mode because functions are
bigger in -race mode, so a few of the helpers for heapBitsBulkBarrier
were not being inlined, and they were not marked nosplit,
so (only in -race mode) the write barrier was being preempted by GC,
causing missed pointer updates.

Filed issue #12069 for diagnosis of any other similar errors.

Fixes #12068.

Change-Id: Ic174d9b050ba278b18b08ab0d85a73c33bd5b175
Reviewed-on: https://go-review.googlesource.com/13364
Reviewed-by: Austin Clements <austin@google.com>
This commit is contained in:
Russ Cox 2015-08-07 13:34:56 -04:00
parent 4a19081358
commit 3ae17043f7
1 changed files with 9 additions and 0 deletions
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9
src/runtime/mbitmap.go
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@ -109,6 +109,9 @@ func add1(p *byte) *byte {
// subtract1 returns the byte pointer p-1.
//go:nowritebarrier
//
// nosplit because it is used during write barriers and must not be preempted.
//go:nosplit
func subtract1(p *byte) *byte {
// Note: wrote out full expression instead of calling subtractb(p, 1)
// to reduce the number of temporaries generated by the
@ -245,6 +248,9 @@ func (h heapBits) prefetch() {
// next returns the heapBits describing the next pointer-sized word in memory.
// That is, if h describes address p, h.next() describes p+ptrSize.
// Note that next does not modify h. The caller must record the result.
//
// nosplit because it is used during write barriers and must not be preempted.
//go:nosplit
func (h heapBits) next() heapBits {
if h.shift < 3*heapBitsShift {
return heapBits{h.bitp, h.shift + heapBitsShift}
@ -293,6 +299,9 @@ func (h heapBits) setMarkedNonAtomic() {
// isPointer reports whether the heap bits describe a pointer word.
// h must describe the initial word of the object.
//
// nosplit because it is used during write barriers and must not be preempted.
//go:nosplit
func (h heapBits) isPointer() bool {
return (*h.bitp>>h.shift)&bitPointer != 0
}