runtime/trace: TestTraceFutileWakeup failure with "no consistent ordering of events possible"

[bcmills]

--- FAIL: TestTraceFutileWakeup (0.07s)
    trace_test.go:146: failed to parse trace: no consistent ordering of events possible
FAIL
FAIL	runtime/trace	4.859s

greplogs --dashboard -md -l -e 'FAIL: TestTraceFutileWakeup'

2022-02-16T16:06:39-f985833/dragonfly-amd64

(CC @mknyszek @prattmic @dvyukov per dev.golang.org/owners.)

This may be just another instance of #29707, but in #29707 (comment) @aclements suggesting that the failure mode reported there may be specific to C threads calling into Go, which doesn't seem to be the case here.

[prattmic]

This is a case where we really need extra files from builders (like #49165).

We could potentially debug this given the malformed trace file. As-is there is basically nothing to work with.

[bcmills]

Is it feasible to have the test dump a serialized trace file to stderr, or would that be too large?

[prattmic]

I've considered that with core dumps. :) But those are definitely too big for the max builder output (2MB IIRC).

I'd have to double-check these, but given the relatively high iteration count in this test, I wouldn't be surprised if it was too big.

[prattmic]

Oh nice, the trace is small enough to dump as a string. I'll send a CL for that.

• 89KB raw trace
• 120KB base64 encoded
• 64KB raw trace gzipped
• 86KB gzipped trace base64 encoded

[gopherbot]

Change https://go.dev/cl/387954 mentions this issue: runtime/trace: dump encoded trace to failure log