linux-kernel - Re: [PATCH RFC] selftests/pidfd: Fix duplicate-symbol warnings for SCHED

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Message-ID: <dbb9ca63-15d5-4547-beb4-5c4044938967@paulmck-laptop>
Date: Fri, 18 Jul 2025 16:56:57 -0700
From: "Paul E. McKenney" <paulmck@...nel.org>
To: Shuah Khan <skhan@...uxfoundation.org>
Cc: Christian Brauner <brauner@...nel.org>, Shuah Khan <shuah@...nel.org>,
	linux-kernel@...r.kernel.org, linux-kselftest@...r.kernel.org
Subject: Re: [PATCH RFC] selftests/pidfd: Fix duplicate-symbol warnings for
 SCHED_ CPP symbols

On Fri, Jul 18, 2025 at 03:03:43PM -0600, Shuah Khan wrote:
> On 7/14/25 17:01, Paul E. McKenney wrote:
> > The pidfd selftests run in userspace and include both userspace and kernel
> > header files.  On some distros (for example, CentOS), this results in
> > duplicate-symbol warnings in allmodconfig builds, while on other distros
> > (for example, Ubuntu) it does not.  (This happens in recent -next trees,
> > including next-20250714.)
> > 
> > Therefore, use #undef to get rid of the userspace definitions in favor
> > of the kernel definitions.
> > 
> > Other ways of handling this include splitting up the selftest code so
> > that the userspace definitions go into one translation unit and the
> > kernel definitions into another (which might or might not be feasible)
> > or to adjust compiler command-line options to suppress the warnings
> > (which might or might not be desirable).
> > 
> > Signed-off-by: Paul E. McKenney <paulmck@...nel.org>
> > Cc: Christian Brauner <brauner@...nel.org>
> > Cc: Shuah Khan <shuah@...nel.org>
> > Cc: <linux-kselftest@...r.kernel.org>
> > 
> > ---
> >   pidfd.h |    4 ++++
> >   1 file changed, 4 insertions(+)
> > 
> > diff --git a/tools/testing/selftests/pidfd/pidfd.h b/tools/testing/selftests/pidfd/pidfd.h
> > index efd74063126eb..6ff495398e872 100644
> > --- a/tools/testing/selftests/pidfd/pidfd.h
> > +++ b/tools/testing/selftests/pidfd/pidfd.h
> > @@ -16,6 +16,10 @@
> >   #include <sys/types.h>
> >   #include <sys/wait.h>
> 
> Please add comments here about why we are adding this so there
> won't be any confusion later.

Good point, thank you!

Like this?

/*
 * Remove the userspace definitions of the following preprocessor symbols
 * to avoid duplicate-definition warnings from the subsequent in-kernel
 * definitions.
 */

> > +#undef SCHED_NORMAL
> > +#undef SCHED_FLAG_KEEP_ALL
> > +#undef SCHED_FLAG_UTIL_CLAMP
> > +
> >   #include "../kselftest.h"
> >   #include "../clone3/clone3_selftests.h"
> 
> With that change:
> 
> Reviewed-by: Shuah Khan <skhan@...uxfoundation.org>

Thank you!

> I am assuming this will go through Christian's tree. If not I can
> take it through mine.

I am of course good either way.  ;-)

							Thanx, Paul