tree 3a0ca687ee9a8cd7051c73f49dcc5f63b07f7b8f
parent 45f14b4bdc3642e57ac01281322f0f698bb2902c
author Damien Neil <dneil@google.com> 1564590559 -0700
committer Damien Neil <dneil@google.com> 1564780163 +0000

internal/impl: fix data race in atomicNilMessage

The problem is that atomicNilMessage.m.mi is accessed both by atomic and
non-atomic operations. (Init uses an atomic read to verify that m.mi is
non-nil, but then returns a non-atomic m.)

Race condition is demonstrated by this test with
"go test -race -count=1000":

	func TestPointer(t *testing.T) {
		var m atomicNilMessage
		var mi MessageInfo
		ch := make(chan *MessageInfo)
		for i := 0; i < 20; i++ {
			go func() {
				r := m.Init(&mi)
				if &mi != r.mi {
					// This conditional exists just
					// ensure r.mi is touched.
					t.Error("mismatch")
				}
				ch <- r.mi
			}()
		}
		for i := 0; i < 20; i++ {
			<-ch
		}
	}

I chose not to add the test since it seems a bit overfit to the specific
situation.

Change-Id: Id4664ef3cd5b29515ed310851b9aeb7561be30d0
Reviewed-on: https://go-review.googlesource.com/c/protobuf/+/188337
Reviewed-by: Joe Tsai <thebrokentoaster@gmail.com>