linux-kernel - Re: locking/local_lock, mm: sparse warnings about shadowed variable

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Message-ID: <CAADnVQK+wjvxmBM7WJOGNK=AqeJ7UHBO4tUZR3Gjc4kfgux1sw@mail.gmail.com>
Date: Wed, 11 Jun 2025 11:20:16 -0700
From: Alexei Starovoitov <alexei.starovoitov@...il.com>
To: Vlastimil Babka <vbabka@...e.cz>
Cc: Charlemagne Lasse <charlemagnelasse@...il.com>, Johannes Weiner <hannes@...xchg.org>, 
	Michal Hocko <mhocko@...nel.org>, Roman Gushchin <roman.gushchin@...ux.dev>, 
	Shakeel Butt <shakeel.butt@...ux.dev>, Muchun Song <muchun.song@...ux.dev>, 
	Andrew Morton <akpm@...ux-foundation.org>, 
	Sebastian Andrzej Siewior <bigeasy@...utronix.de>, Clark Williams <clrkwllms@...nel.org>, 
	Steven Rostedt <rostedt@...dmis.org>, Alexei Starovoitov <ast@...nel.org>, 
	Thomas Gleixner <tglx@...utronix.de>, Jakub Kicinski <kuba@...nel.org>, 
	"Peter Zijlstra (Intel)" <peterz@...radead.org>, Davidlohr Bueso <dave@...olabs.net>, 
	LKML <linux-kernel@...r.kernel.org>, 
	"open list:CONTROL GROUP (CGROUP)" <cgroups@...r.kernel.org>, linux-mm <linux-mm@...ck.org>, 
	linux-rt-devel@...ts.linux.dev
Subject: Re: locking/local_lock, mm: sparse warnings about shadowed variable

On Wed, Jun 11, 2025 at 10:57 AM Vlastimil Babka <vbabka@...e.cz> wrote:
>
> On 6/11/25 19:37, Charlemagne Lasse wrote:
> > HI,
> >
> > when I run `make C=2 mm/mlock.o CHECK="sparse -Wshadow"`, I get a lot of
> >
> > ./include/linux/local_lock.h:88:1: warning: symbol 'l' shadows an earlier one
> > ./include/linux/local_lock.h:88:1: originally declared here
> >
> > after commit
> >
> > 51339d99c0131bc0d16d378e9b05bc498d2967e2 is the first bad commit
> > commit 51339d99c0131bc0d16d378e9b05bc498d2967e2
> > Author: Alexei Starovoitov <ast@...nel.org>
> > Date:   2025-04-02 19:55:14 -0700
> >
> >    locking/local_lock, mm: replace localtry_ helpers with local_trylock_t type
>
> Looks like __DEFINE_LOCK_GUARD_1() has "_type *l" and __local_lock_acquire()
> has "local_lock_t *l;". It can be fixed e.g. like this, although it's
> harmless? The _release() part is not necessary, just for symmetry.
>
> diff --git a/include/linux/local_lock_internal.h b/include/linux/local_lock_internal.h
> index 8d5ac16a9b17..075338f270d0 100644
> --- a/include/linux/local_lock_internal.h
> +++ b/include/linux/local_lock_internal.h
> @@ -97,17 +97,17 @@ do {                                                                \
>  #define __local_lock_acquire(lock)                                     \
>         do {                                                            \
>                 local_trylock_t *tl;                                    \
> -               local_lock_t *l;                                        \
> +               local_lock_t *ll;                                       \

I wouldn't bother messing with the code because of sparse.
Compilers don't warn here.