linux-kernel - Re: [PATCH] x86: bug.h: merge annotate_reachable into _BUG_FLAGS for __WARN

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Date:   Wed, 23 Mar 2022 12:41:31 -0700
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     Charlemagne Lasse <charlemagnelasse@...il.com>,
        Vincent Mailhol <mailhol.vincent@...adoo.fr>,
        jpoimboe@...hat.com
Cc:     adobriyan@...il.com, bp@...en8.de, dave.hansen@...ux.intel.com,
        hpa@...or.com, linux-kernel@...r.kernel.org,
        linux-sparse@...r.kernel.org, llvm@...ts.linux.dev,
        luc.vanoostenryck@...il.com, mingo@...hat.com, nathan@...nel.org,
        peterz@...radead.org, tglx@...utronix.de, x86@...nel.org,
        Sasha Levin <sashal@...nel.org>
Subject: Re: [PATCH] x86: bug.h: merge annotate_reachable into _BUG_FLAGS for __WARN_FLAGS

On Wed, Mar 23, 2022 at 12:30 PM Charlemagne Lasse
<charlemagnelasse@...il.com> wrote:
>
> > @@ -75,9 +77,9 @@ do {                                \
> >   */
> >  #define __WARN_FLAGS(flags)                    \
> >  do {                                \
> > +    __auto_type f = BUGFLAG_WARNING|(flags);        \
> >      instrumentation_begin();                \
> > -    _BUG_FLAGS(ASM_UD2, BUGFLAG_WARNING|(flags));        \
> > -    annotate_reachable();                    \
> > +    _BUG_FLAGS(ASM_UD2, f, ASM_REACHABLE);            \
> >      instrumentation_end();                    \
> >  } while (0)
>
> This causes following sparse warning on x86:
>
> make allnoconfig && touch init/version.c && make CHECK="sparse
> -Wshadow"  C=1 init/version.o
> #
> # No change to .config
> #
>  CALL    scripts/checksyscalls.sh
>  CALL    scripts/atomic/check-atomics.sh
>  CHK     include/generated/compile.h
>  CC      init/version.o
>  CHECK   init/version.c
> init/version.c: note: in included file (through
> include/linux/rculist.h, include/linux/pid.h, include/linux/sched.h,
> include/linux/utsname.h):
> ./include/linux/rcupdate.h:1007:9: warning: symbol 'f' shadows an earlier one
> ./include/linux/rcupdate.h:1001:47: originally declared here

Thanks for the report. There was already a fix sent for this:
https://lore.kernel.org/lkml/20220317065743.8467-1-mailhol.vincent@wanadoo.fr/
but it doesn't mention that sparse is warning about this, too.

I think if Vincent sent a v3 that mentioned that sparse is warning
about this, too, and cc'ed you, you could then supply
signed-off/tested-by tags (or just do so on v2, though it doesn't
mention sparse), and maybe Josh would be so kind as to pick that up?

>
>
> Affected versions (from the ones on kernel.org):
>
> * 5.17 - bfb1a7c91fb7 ("x86/bug: Merge annotate_reachable() into
> _BUG_FLAGS() asm")
> * 5.16.17 - fe0c95903a68 ("x86/bug: Merge annotate_reachable() into
> _BUG_FLAGS() asm")
>
> Cannot be seen when changing the variable name:
>
> diff --git a/arch/x86/include/asm/bug.h b/arch/x86/include/asm/bug.h
> index bab883c0b6fe..cbd11e38252a 100644
> --- a/arch/x86/include/asm/bug.h
> +++ b/arch/x86/include/asm/bug.h
> @@ -77,9 +77,9 @@ do {                                \
>   */
>  #define __WARN_FLAGS(flags)                    \
>  do {                                \
> -    __auto_type f = BUGFLAG_WARNING|(flags);        \
> +    __auto_type __f = BUGFLAG_WARNING|(flags);        \
>      instrumentation_begin();                \
> -    _BUG_FLAGS(ASM_UD2, f, ASM_REACHABLE);            \
> +    _BUG_FLAGS(ASM_UD2, __f, ASM_REACHABLE);            \
>      instrumentation_end();                    \
>  } while (0)



-- 
Thanks,
~Nick Desaulniers