diff options
Diffstat (limited to 'src')
| -rw-r--r-- | src/runtime/mgcmark.go | 20 | ||||
| -rw-r--r-- | src/runtime/mgcsweepbuf.go | 15 |
2 files changed, 19 insertions, 16 deletions
diff --git a/src/runtime/mgcmark.go b/src/runtime/mgcmark.go index 10b525b2bc..e02c874f66 100644 --- a/src/runtime/mgcmark.go +++ b/src/runtime/mgcmark.go @@ -315,15 +315,21 @@ func markrootSpans(gcw *gcWork, shard int) { sg := mheap_.sweepgen spans := mheap_.sweepSpans[mheap_.sweepgen/2%2].block(shard) // Note that work.spans may not include spans that were - // allocated between entering the scan phase and now. This is - // okay because any objects with finalizers in those spans - // must have been allocated and given finalizers after we - // entered the scan phase, so addfinalizer will have ensured - // the above invariants for them. - for _, s := range spans { + // allocated between entering the scan phase and now. We may + // also race with spans being added into sweepSpans when they're + // just created, and as a result we may see nil pointers in the + // spans slice. This is okay because any objects with finalizers + // in those spans must have been allocated and given finalizers + // after we entered the scan phase, so addfinalizer will have + // ensured the above invariants for them. + for i := 0; i < len(spans); i++ { + // sweepBuf.block requires that we read pointers from the block atomically. + // It also requires that we ignore nil pointers. + s := (*mspan)(atomic.Loadp(unsafe.Pointer(&spans[i]))) + // This is racing with spans being initialized, so // check the state carefully. - if s.state.get() != mSpanInUse { + if s == nil || s.state.get() != mSpanInUse { continue } // Check that this span was swept (it may be cached or uncached). diff --git a/src/runtime/mgcsweepbuf.go b/src/runtime/mgcsweepbuf.go index 0491f7ccf6..78288229c8 100644 --- a/src/runtime/mgcsweepbuf.go +++ b/src/runtime/mgcsweepbuf.go @@ -111,8 +111,9 @@ retry: unlock(&b.spineLock) } - // We have a block. Insert the span. - block.spans[bottom] = s + // We have a block. Insert the span atomically, since there may be + // concurrent readers via the block API. + atomic.StorepNoWB(unsafe.Pointer(&block.spans[bottom]), unsafe.Pointer(s)) } // pop removes and returns a span from buffer b, or nil if b is empty. @@ -147,7 +148,9 @@ func (b *gcSweepBuf) numBlocks() int { } // block returns the spans in the i'th block of buffer b. block is -// safe to call concurrently with push. +// safe to call concurrently with push. The block may contain nil +// pointers that must be ignored, and each entry in the block must be +// loaded atomically. func (b *gcSweepBuf) block(i int) []*mspan { // Perform bounds check before loading spine address since // push ensures the allocated length is at least spineLen. @@ -169,11 +172,5 @@ func (b *gcSweepBuf) block(i int) []*mspan { } else { spans = block.spans[:bottom] } - - // push may have reserved a slot but not filled it yet, so - // trim away unused entries. - for len(spans) > 0 && spans[len(spans)-1] == nil { - spans = spans[:len(spans)-1] - } return spans } |