runtime/pprof: TestBlockProfile failures with "Bad mutex entry"

[bcmills]

--- FAIL: TestBlockProfile (0.18s)
    --- FAIL: TestBlockProfile/debug=1 (0.00s)
        pprof_test.go:707: Bad mutex entry, expect:
…            
    --- FAIL: TestBlockProfile/proto (0.00s)
 …
        pprof_test.go:728: No matching stack entry for mutex, want [sync.(*Mutex).Lock runtime/pprof.blockMutex runtime/pprof.TestBlockProfile]
FAIL
FAIL	runtime/pprof	5.161s

CC @hyangah @pjweinbgo

2020-03-12T23:17:02-5d70cb0/linux-ppc64-buildlet
2020-03-12T20:00:02-e221a75/linux-ppc64-buildlet
2020-03-02T16:24:47-d7c073e/darwin-arm64-mn4m2zdaios
2020-01-19T15:28:32-02816a2/darwin-arm64-mn4m2zdaios
2019-11-18T14:40:07-afac2c0/darwin-arm64-mn4m2zdaios

[bcmills]

See also #6999 (possibly the same root cause).

Looks like the test is somehow missing a profile entry.

[bcmills]

2020-06-08T15:44:05-bb89014/linux-s390x-ibm

[odeke-em]

@rsc's text/template CL https://go-review.googlesource.com/c/go/+/254257 just experienced this on android-amd64-emu with https://storage.googleapis.com/go-build-log/be762e2e/android-amd64-emu_b91dd69a.log.

[bcmills]

https://storage.googleapis.com/go-build-log/62659877/android-amd64-emu_22bb6d10.log (a TryBot)

[gopherbot]

Change https://go.dev/cl/384534 mentions this issue: runtime/pprof: skip TestBlockProfile