linux-kernel - Re: [PATCH] locking/mutex: annotate __devm_mutex_init() with __must

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Message-ID: <CAMRc=Mc-GGsr0Fpfi3hzoH4UGkHeaXQQUvQ2NR=kjbzsotYHWA@mail.gmail.com>
Date: Mon, 7 Apr 2025 09:23:07 +0200
From: Bartosz Golaszewski <brgl@...ev.pl>
To: Thomas Weißschuh <thomas.weissschuh@...utronix.de>
Cc: Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...hat.com>, 
	Will Deacon <will@...nel.org>, Boqun Feng <boqun.feng@...il.com>, Waiman Long <longman@...hat.com>, 
	linux-kernel@...r.kernel.org, 
	Bartosz Golaszewski <bartosz.golaszewski@...aro.org>
Subject: Re: [PATCH] locking/mutex: annotate __devm_mutex_init() with __must_check

On Mon, Apr 7, 2025 at 9:21 AM Thomas Weißschuh
<thomas.weissschuh@...utronix.de> wrote:
>
> On Mon, Apr 07, 2025 at 09:03:46AM +0200, Bartosz Golaszewski wrote:
> > From: Bartosz Golaszewski <bartosz.golaszewski@...aro.org>
> >
> > Unlike the non-managed mutex_init(), devm_mutex_init() can fail (for
> > instance: on OOM). Now that we've fixed all instances of users not
> > checking the return value, annotate it with __must_check to avoid this
> > problem in the future.
> >
> > Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@...aro.org>
> > ---
> >  include/linux/mutex.h | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/include/linux/mutex.h b/include/linux/mutex.h
> > index 2143d05116be..e194f8c22d72 100644
> > --- a/include/linux/mutex.h
> > +++ b/include/linux/mutex.h
> > @@ -126,7 +126,7 @@ do {                                                      \
> >
> >  #ifdef CONFIG_DEBUG_MUTEXES
> >
> > -int __devm_mutex_init(struct device *dev, struct mutex *lock);
> > +int __must_check __devm_mutex_init(struct device *dev, struct mutex *lock);
>
> This didn't work for me, see [0].
>
>         "Unfortunately __must_check/warn_unused_result don't propagate through
>         statement expression."
>
> Also it is missing the !CONFIG_DEBUG_MUTEXES case.
> I'll resend my patch once more.
>
>
> [0] https://lore.kernel.org/lkml/20250208-must_check-devm_mutex_init-v3-2-245e417dcc9e@weissschuh.net/
>

Thanks, I should have actually tested it, duh.

Bartosz