linux-kernel - Re: [PATCH 3/4] bitmap: define a cleanup function for bitmaps

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Message-ID: <CAMRc=MeGXHj2bMsbqS=AK_R2V5EttPw016TO1ZU3HXhEV-tqXQ@mail.gmail.com>
Date:   Mon, 14 Aug 2023 09:13:32 +0200
From:   Bartosz Golaszewski <brgl@...ev.pl>
To:     Yury Norov <yury.norov@...il.com>
Cc:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        Thomas Gleixner <tglx@...utronix.de>,
        linux-kernel@...r.kernel.org,
        Bartosz Golaszewski <bartosz.golaszewski@...aro.org>
Subject: Re: [PATCH 3/4] bitmap: define a cleanup function for bitmaps

On Mon, Aug 14, 2023 at 3:02 AM Yury Norov <yury.norov@...il.com> wrote:
>
> On Sat, Aug 12, 2023 at 09:44:56PM +0200, Bartosz Golaszewski wrote:
> > From: Bartosz Golaszewski <bartosz.golaszewski@...aro.org>
> >
> > Add support for autopointers for bitmaps allocated with bitmap_alloc()
> > et al.
> >
> > Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@...aro.org>
> > ---
> >  include/linux/bitmap.h | 3 +++
> >  1 file changed, 3 insertions(+)
> >
> > diff --git a/include/linux/bitmap.h b/include/linux/bitmap.h
> > index 03644237e1ef..6709807ebb59 100644
> > --- a/include/linux/bitmap.h
> > +++ b/include/linux/bitmap.h
> > @@ -6,6 +6,7 @@
> >
> >  #include <linux/align.h>
> >  #include <linux/bitops.h>
> > +#include <linux/cleanup.h>
> >  #include <linux/find.h>
> >  #include <linux/limits.h>
> >  #include <linux/string.h>
> > @@ -125,6 +126,8 @@ unsigned long *bitmap_alloc_node(unsigned int nbits, gfp_t flags, int node);
> >  unsigned long *bitmap_zalloc_node(unsigned int nbits, gfp_t flags, int node);
> >  void bitmap_free(const unsigned long *bitmap);
> >
> > +DEFINE_FREE(bitmap, unsigned long *, if (_T) bitmap_free(_T))
>
> bitmap_free() is a wrapper around kfree(), and kfree() checks against
> NULL, and returns immediately. Why this tests again?

I don't see any kernel docs making it a contract though. :)

It's a good question however. I carried it over from the kfree()'s
DEFINE_FREE() itself. I can't find any discussion about it in the
thread under Peter Zijlstra's patches.

May be worth revisiting it for free() functions that handle NULL.

Bart