Date: Tue, 25 Apr 2017 19:22:53 -0700 From: Ngie Cooper <yaneurabeya@gmail.com> To: Brooks Davis <brooks@freebsd.org> Cc: "freebsd-hackers@freebsd.org" <freebsd-hackers@freebsd.org>, Alan Somers <asomers@freebsd.org>, "bdrewery@freebsd.org" <bdrewery@freebsd.org>, "freebsd-testing@freebsd.org" <freebsd-testing@freebsd.org> Subject: Re: racy tests Message-ID: <CAGHfRMD9DtJOXugffdpXwNjg-XaUE6%2BOW-gCU56Rb8STjDu7aA@mail.gmail.com> In-Reply-To: <20170425230247.GA8201@spindle.one-eyed-alien.net> References: <20170425230247.GA8201@spindle.one-eyed-alien.net>
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On Tue, Apr 25, 2017 at 4:02 PM, Brooks Davis <brooks@freebsd.org> wrote:
> I've been running the FreeBSD test suite for mips64 under qemu. As a
> result, I'm seeing some tests fail due to assumptions about timing producing
> test races. For example one of the pwait tests does this:
>
> timeout_many_body()
> {
> sleep 1 &
> p1=$!
>
> sleep 5 &
> p5=$!
>
> sleep 10 &
> p10=$!
>
> atf_check \
> -o empty \
> -e empty \
> -s exit:124 \
> timeout --preserve-status 7.5 pwait -t 6 $p1 $p5 $p10
> }
>
> Under emulation, particularly if the host disks are busy, it's easily
> possible for the first sleep to exit before pwait actually runs.
> In practice, we could probably get away with cranking up the times a
> fair bit, but that would make the test slow and the race would still
> exist.
>
> Any thoughts about the right solution? Something not time based would
> be ideal, but then it seems like we'd need a parallel process to kill
> some of the waited for victims we quickly end up with something more
> complicated than pwait that also needs testing...
(Adding bdrewery@, testing@)
I need to think about this a bit. The issue might be that we're using
the wrong timer for sleep(1)/need to account for being interrupted.
Needless to say, emulation really screws up timing assumptions because
virtual clocks don't function like hardware clocks.
Thanks,
-Ngie
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