linux-kernel - Re: [PATCH] include/asm/cmpxchg.h: Remove duplicate header

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Date:   Fri, 2 Nov 2018 12:14:50 -0700
From:   Matt Turner <mattst88@...il.com>
To:     jrdr.linux@...il.com
Cc:     Michael Cree <mcree@...on.net.nz>, brajeswar.linux@...il.com,
        Richard Henderson <rth@...ddle.net>,
        Ivan Kokshaysky <ink@...assic.park.msu.ru>,
        Andrea Parri <parri.andrea@...il.com>,
        Ingo Molnar <mingo@...nel.org>,
        "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
        linux-alpha <linux-alpha@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>, sabyasachi.linux@...il.com
Subject: Re: [PATCH] include/asm/cmpxchg.h: Remove duplicate header

On Fri, Nov 2, 2018 at 12:09 PM Souptick Joarder <jrdr.linux@...il.com> wrote:
>
> On Sat, Nov 3, 2018 at 12:31 AM Matt Turner <mattst88@...il.com> wrote:
> >
> > On Fri, Nov 2, 2018 at 11:55 AM Souptick Joarder <jrdr.linux@...il.com> wrote:
> > > We run the static analyser "make includecheck" which list out files where
> > > duplicate headers can be removed and based on that we thought to remove
> > > from this file. Didn't understood about the existence of second include ??
> >
> >
> > #define ____xchg(type, args...)         __xchg ## type ## _local(args)
> > #define ____cmpxchg(type, args...)      __cmpxchg ## type ## _local(args)
> > #include <asm/xchg.h>
> > [snip]
> > #undef ____xchg
> > #undef ____cmpxchg
> > #define ____xchg(type, args...)         __xchg ##type(args)
> > #define ____cmpxchg(type, args...)      __cmpxchg ##type(args)
> > #include <asm/xchg.h>
> >
> > asm/xchg.h has a comment at the top that says
> >
> > /*
> >  * xchg/xchg_local and cmpxchg/cmpxchg_local share the same code
> >  * except that local version do not have the expensive memory barrier.
> >  * So this file is included twice from asm/cmpxchg.h.
> >  */
>
> Thanks Matt. Sorry for the noise.
> Is there any way to exclude it from static analyser that someone else will
> not do the same mistake in future ?

Since this is not an uncommon pattern in C, I think any static
analysis tool that attempts to find duplicate includes should attempt
to recognize such a pattern.

That, or humans should review the output of their static analysis
tools. Or you could try to compile the patches produced. I think any
of those would have caught the problem with the patch.