all: plan9-arm builder failing frequently with a variety of errors

[bcmills]

#!watchflakes
post <- builder ~ `plan9-arm`

The one remaining plan9 builder is failing a significant fraction of build attempts.
Many of the failures follow specific known patterns (notably #49337, #46526, and #41952). However, many do not.

@millerresearch, @0intro, @fhs: is there someone who can investigate these failures and bring the plan9 port back up to par? With the 0intro builders missing (#49327, #49328), there is no longer any plan9 builder consistently passing tests.

greplogs --dashboard -md -l -e \\Aplan9. -E . --since=2021-10-01

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[millerresearch]

For most of plan9-arm failures, the cause is filesystem flakiness on the builder machines (a cluster of 3 x raspberry pi 4). I've just reconfigured the build script to stop using ramfs (which has a locking bug) for /tmp, and stop using the ad hoc directory cache (which still seems to have some flaws). This should bypass most of the failures but will make the test suite a lot slower to run (by go.17 it had already regressed to about 2 hours even with these filesystem tweaks).

There are some other flakes of the "shouldn't be possible" variety, which are are rare and perplexing and impossible to replicate. They are occurring in general go runtime code, not specific to plan 9. There's a slight whiff of possible memory cache coherence trouble in some of these:
marked free object in span
attempt to clean non-empty span set
unexpected waitm - semaphore out of sync
runtime: cannot allocate memory
not inlined: unknown reason

It would be good to have a server-class ARM platform capable of running plan 9 as a more reliable builder. I don't know of one.

[bcmills]

Looks like the filesystem change did resolve at least one class of failure: the '/boot/workdir/go/src/os' does not exit failure mode hasn't occurred at all in November so far.

greplogs --dashboard -md -l -e \''/boot/workdir/go/src/os'\'' does not exist'

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2021-10-25T17:02:16-52b10ab/plan9-arm
2021-10-19T18:18:37-9820602/plan9-arm
2021-10-10T15:11:26-d2d21d9/plan9-arm
2021-10-09T23:29:26-b99abf3/plan9-arm
2021-10-07T19:56:19-4ab3c10/plan9-arm
2021-10-01T18:18:46-0d65c27/plan9-arm
2021-09-27T18:58:36-5b90958/plan9-arm
2021-09-21T20:39:31-48cf96c/plan9-arm
2021-09-21T00:59:39-d1fd3eb/plan9-arm
2021-08-28T01:49:50-f371b30/plan9-arm
2021-08-22T22:04:02-5d5e50c/plan9-arm
2021-08-13T21:43:20-a95f1b5/plan9-arm
2021-07-25T17:16:20-849b791/plan9-arm
2021-06-17T03:25:37-b0355a3/plan9-arm
2021-05-25T23:41:42-74242ba/plan9-arm
2021-03-29T20:35:19-164a626/plan9-arm
2021-03-04T06:36:33-868a110/plan9-arm
2021-02-24T19:25:49-bf48163/plan9-arm
2020-10-13T00:31:47-5ef78c4/plan9-arm
2020-10-12T14:44:34-0f53453/plan9-arm
2020-08-18T15:50:52-b58d297/plan9-arm
2020-05-05T19:42:01-0e617d3/plan9-arm

[gopherbot]

Change https://golang.org/cl/362975 mentions this issue: dashboard: omit the website repo on plan9

[bcmills]

Many of the failure modes seem to have cleared up around 11 Nov.; it's not clear to me what fixed them.

One of the failures visible on the dashboard today is #49653; the other is the marked free object in span failure mode.

[bcmills]

A few more failure modes that remain:
#22227 (unexpected signal in os.StartProcess)
#49684 (panic during panic)
#49691 (unexpected stale targets)

[gopherbot]

Change https://golang.org/cl/369018 mentions this issue: src/cmd/go/internal/work: lock Builder output mutex consistently

[gopherbot]

Change https://golang.org/cl/380414 mentions this issue: message/pipeline: skip TestFullCycle on plan9-arm

[bcmills]

A sampling from the past week or so. Undiagnosed failures in bold.

greplogs --dashboard -md -l -e \\Aplan9-arm -E . --since=2022-01-20

2022-01-27T05:30:27-be5769c-a991d9d/plan9-arm

panic: test timed out after 10m0s
…
goroutine 6 [select, 9 minutes]:
…
golang.org/x/tools/go/packages.goListDriver(0x1695ab84, {0x175c8c78, 0x1, 0x1})
	/boot/workdir/gopath/src/golang.org/x/tools/go/packages/golist.go:200 +0x7b0
…
FAIL	golang.org/x/tools/gopls/doc	600.515s

That's stuck running go list:
https://cs.opensource.google/go/x/tools/+/master:go/packages/golist.go;l=447;drc=eb48d3f608bba06c3bb4f5627f9fc2562cc84dd2

2022-01-27T05:30:27-bbe1937-a991d9d/plan9-arm (#50857)
2022-01-27T05:30:27-aa10faf-a991d9d/plan9-arm (#50857)
2022-01-27T00:03:31-bbe1937-f4aa021/plan9-arm (#50857)
2022-01-26T23:43:39-be5769c-db48840/plan9-arm (probably #46520, not specific to plan9)
2022-01-26T23:43:39-bbe1937-db48840/plan9-arm (#50857)
2022-01-26T22:33:26-ef0b09c/plan9-arm (possibly #22227?)
2022-01-26T22:09:36-bbe1937-ca6a5c0/plan9-arm (#50857)
2022-01-26T21:43:32-be5769c-c8b0dce/plan9-arm (#46520, not specific to plan9)
2022-01-26T20:51:54-fe74b5f-c8b0dce/plan9-arm (#46520, not specific to plan9)
2022-01-26T17:58:00-bbe1937-719e989/plan9-arm (#50857)
2022-01-25T22:56:45-c20fd7c-6eb58cd/plan9-arm (#46520, not specific to plan9)
2022-01-25T22:04:10-c20fd7c-38729cf/plan9-arm (#46520, not specific to plan9)
2022-01-25T00:39:08-97de9ec-16d6a52/plan9-arm (#46520, not specific to plan9)
2022-01-24T21:27:20-cdd9e93/plan9-arm

--- FAIL: TestIntendedInlining (15.35s)
    inl_test.go:267: exit status: 'go 32037: 2'
FAIL
FAIL	cmd/compile/internal/test	119.720s

2022-01-24T16:42:11-2cc1836-19d819d/plan9-arm (#50775, mitigated)
2022-01-21T23:16:33-3c751cd-b7fa0f9/plan9-arm (#50775, mitigated)
2022-01-21T21:58:14-3c751cd-35b0db7/plan9-arm (#50775, mitigated)
2022-01-21T21:58:14-35b0db7/plan9-arm

panic: test timed out after 18m0s
…
goroutine 185 [chan receive, 17 minutes]:
…
os/exec.(*Cmd).CombinedOutput(0x110ae000)
	/boot/workdir/go/src/os/exec/exec.go:567 +0x98 fp=0x11105e2c sp=0x11105e18 pc=0x12b1dc
cmd/compile/internal/test.TestCode(0x10c02f00)
	/boot/workdir/go/src/cmd/compile/internal/test/ssa_test.go:171 +0x9fc fp=0x11105f98 sp=0x11105e2c pc=0x3af55c
…
FAIL	cmd/compile/internal/test	1080.192s

That's running a go test -c subprocess, but without a timeout so we don't get a useful goroutine dump to debug it 😞:
https://cs.opensource.google/go/go/+/master:src/cmd/compile/internal/test/ssa_test.go;l=171;drc=16a3cefc93d9b896b2053320e387d0e449904aba

2022-01-21T21:27:57-e7c9de2-9eba5ff/plan9-arm (#46520, not specific to plan9)
2022-01-21T21:08:53-3425967-9eba5ff/plan9-arm (#50775, mitigated)
2022-01-21T16:59:19-9f83dd3-9eba5ff/plan9-arm (#50775, mitigated)
2022-01-20T20:23:52-80963bc-2c2e081/plan9-arm (#46520, not specific to plan9)
2022-01-20T14:59:17-ab35822-9284279/plan9-arm (#46520, not specific to plan9)
2022-01-20T14:52:25-ab35822-e7d5857/plan9-arm (possibly #45211? if so, not specific to plan9)

[gopherbot]

Change https://go.dev/cl/408697 mentions this issue: dashboard: add known issues for plan9-arm