x/sys/unix: TestPidfd fails on GOARCH mips builders

[mdlayher]

I implemented unix.Waitid in https://go-review.googlesource.com/c/sys/+/395936/, and @tklauser commented:

This CL seems to break the mips64-rtk, mips64le-rtk and mipsle-rtk builders:

 --- FAIL: TestPidfd (0.00s)
    syscall_linux_test.go:243: failed to check for child exit: invalid argument
FAIL
FAIL	[golang.org/x/sys/unix](http://golang.org/x/sys/unix)	0.684s

https://build.golang.org/log/405cfcebea4c1b0f00de4d988c2b1baf527b8008
https://build.golang.org/log/c2446e254921d971f655b00c86d5cb3aa2957e1a
https://build.golang.org/log/650f8e0343be7531952a38c71957f33ee6272e66

Maybe kernel version is too old on these builders?

For now, I will add a skip on EINVAL in this test.

/cc @tklauser @ianlancetaylor

[gopherbot]

Change https://go.dev/cl/396154 mentions this issue: unix: skip Linux TestPidfd if Waitid returns EINVAL

[mdlayher]

Ping @bogojevic @milanknezevic and @mengzhuo as the owners of these builders.

[mengzhuo]

linux-mipsle-mengzhuo runs on 5.4.110 is it affected?

[draganmladjenovic]

@mdlayher It looks like pidfd_open is introduced during 5.3 and waitid with P_PIDFD is introduced in 5.4. These machines are at 5.3.3*.

[mdlayher]

Any chance these builders could be bumped to 5.10.x LTS? I believe that'd solve the immediate problem.

I don't have any context on mips or the builders, I'm just reporting what Tobias told me above. See logs.

[draganmladjenovic]

Not in the meantime. Not sure if there is another pidfd* syscall that can be easily used to construct the test instead of waitid.

[mdlayher]

The test can stay skipped for now, no problem. Thanks.

[ianlancetaylor]

The tests should pass on older (but still supported) kernel versions, and it sounds like that is what is happening now. So there is nothing to do. Closing. Thanks all.