linux-kernel - Re: [PATCH v2] coccinelle: fix parallel build with CHECK=scripts/coccicheck

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Date:   Tue, 14 Nov 2017 07:44:43 +0100 (CET)
From:   Julia Lawall <julia.lawall@...6.fr>
To:     Masahiro Yamada <yamada.masahiro@...ionext.com>
cc:     Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>,
        cocci@...teme.lip6.fr, Nicolas Palix <nicolas.palix@...g.fr>,
        Gilles Muller <Gilles.Muller@...6.fr>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Michal Marek <michal.lkml@...kovi.net>
Subject: Re: [PATCH v2] coccinelle: fix parallel build with
 CHECK=scripts/coccicheck



On Tue, 14 Nov 2017, Masahiro Yamada wrote:

> Hi Julia,
>
> 2017-11-14 1:45 GMT+09:00 Julia Lawall <julia.lawall@...6.fr>:
> >
> >
> > On Tue, 14 Nov 2017, Masahiro Yamada wrote:
> >
> >> Hi Julia,
> >>
> >>
> >> 2017-11-14 0:30 GMT+09:00 Julia Lawall <julia.lawall@...6.fr>:
> >> >
> >> >
> >> > On Thu, 9 Nov 2017, Masahiro Yamada wrote:
> >> >
> >> >> The command "make -j8 C=1 CHECK=scripts/coccicheck" produces lots of
> >> >> "coccicheck failed" error messages.
> >> >>
> >> >> I do not know the coccinelle internals, but I guess --jobs does not
> >> >> work well if spatch is invoked from Make running in parallel.
> >> >> Disable --jobs in this case.
> >> >
> >> > Why is this change under:
> >> >
> >> > if [ "$C" = "1" -o "$C" = "2" ];
> >> >
> >> > The coccicheck failed messages come also if one runs Coccinelle on the
> >> > entire kernel.
> >>
> >> As far as I tested, "coccicheck failed" error only happens
> >> when ONLINE=1.
> >>
> >>
> >> make -j8 C=1 CHECK=scripts/coccicheck  COCCI=scripts/coccinelle/misc/bugon.cocci
> >>
> >> emits lots of errors.
> >>
> >>
> >> make -j8 coccicheck  COCCI=scripts/coccinelle/misc/bugon.cocci
> >>
> >> is fine.
> >>
> >>
> >> Have you tested it?
> >> Do you mean you got a different result from mine?
> >
> > I agree with your results, with respect to the number of errors.
> >
> > julia
> >
>
> So, what shall we do?
>
> If you do not like to fix it (or you can fix coccinelle itself),
> I can take back this patch.

I'm OK with your fix.  I will check and ack it today.

> I am not a coccinelle developer, so
> setting USE_JOBS="no" is the best I can do.

The problem on the Coccinelle side is that it uses a subdirectory with the
name of the semantic patch to store standard output and standard error for
the different threads.  I didn't want to use a name with the pid, so that
one could easily find this information while Coccinelle is running.
Normally the subdirectory is cleaned up when Coccinelle completes, so
there is only one of them at a time.  Maybe it is best to just add the
pid.  There is the risk that these subdirectories will accumulate if
Coccinelle crashes in a way such that they don't get cleaned up, but
Coccinelle could print a warning if it detects this case, rather than
failing.

Still I think it is useful to do something on the make coccicheck side,
because there is no need for the double layer of parallelism.

julia