linux-kernel - Re: [PATCH 1/1] sh: add support for cmpxchg on u8 and u16 pointers

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Message-Id: <C510813DTTYI.1PZXLO9Y2FRLM@atris>
Date:   Wed, 19 Aug 2020 09:23:47 -0400
From:   "Liam Beguin" <liambeguin@...il.com>
To:     "Geert Uytterhoeven" <geert@...ux-m68k.org>
Cc:     "Yoshinori Sato" <ysato@...rs.sourceforge.jp>,
        "Rich Felker" <dalias@...c.org>,
        "Linux-sh list" <linux-sh@...r.kernel.org>,
        "Linux Kernel Mailing List" <linux-kernel@...r.kernel.org>,
        "kernel test robot" <lkp@...el.com>
Subject: Re: [PATCH 1/1] sh: add support for cmpxchg on u8 and u16 pointers

Hi Geert,

On Wed Aug 19, 2020 at 5:09 AM EDT, Geert Uytterhoeven wrote:
> Hi Liam,
>
> On Wed, Aug 19, 2020 at 5:07 AM Liam Beguin <liambeguin@...il.com>
> wrote:
> > The kernel test bot reported[1] that using set_mask_bits on a u8 causes
> > the following issue on SuperH:
> >
> >     >> ERROR: modpost: "__cmpxchg_called_with_bad_pointer" [drivers/phy/ti/phy-tusb1210.ko] undefined!
> >
> > Add support for cmpxchg on u8 and u16 pointers.
> >
> > [1] https://lore.kernel.org/patchwork/patch/1288894/#1485536
> >
> > Reported-by: kernel test robot <lkp@...el.com>
> > Signed-off-by: Liam Beguin <liambeguin@...il.com>
> > ---
> >
> > Hi,
> >
> > This was reported by the kernel test bot on an architecture I can't
> > really test on. I was only able to make sure the build succeeds, but
> > nothing more.
> > This patch is based on the __cmpxchg_u32 impletmentation and seems
> > incomplete based on the different cmpxchg headers I can find.
>
> Indeed. This version is suitable for non-SMP machines only.
> BTW, it looks like this version can be replaced by the one in
> asm-generic?
>

Thanks for your feedback I'll have a look at the asm-generic functions
and try to use those instead.

> >
> > Do these function need to be impletmented in each header
> > simulataneously?
>
> Yes, we need them for all variants.
>

Okay, I'll look into that. Would you recommend a good way to test these
changes?

> >  arch/sh/include/asm/cmpxchg-irq.h | 27 +++++++++++++++++++++++++++
> >  arch/sh/include/asm/cmpxchg.h     |  5 +++--
> >  2 files changed, 30 insertions(+), 2 deletions(-)
> >
> > diff --git a/arch/sh/include/asm/cmpxchg-irq.h b/arch/sh/include/asm/cmpxchg-irq.h
> > index 07d3e7f08389..918c4153a930 100644
> > --- a/arch/sh/include/asm/cmpxchg-irq.h
> > +++ b/arch/sh/include/asm/cmpxchg-irq.h
> > @@ -51,4 +51,31 @@ static inline unsigned long __cmpxchg_u32(volatile int *m, unsigned long old,
> >         return retval;
> >  }
> >
> > +static inline unsigned long __cmpxchg_u16(volatile u16 *m, unsigned long old,
> > +       unsigned long new)
> > +{
> > +       u16 retval;
> > +       unsigned long flags;
> > +
> > +       local_irq_save(flags);
> > +       retval = *m;
> > +       if (retval == old)
> > +               *m = new;
> > +       local_irq_restore(flags);
> > +       return (unsigned long)retval;
> > +}
> > +
> > +static inline unsigned long __cmpxchg_u8(volatile u8 *m, unsigned long old,
> > +       unsigned long new)
> > +{
> > +       u8 retval;
> > +       unsigned long flags;
> > +
> > +       local_irq_save(flags);
> > +       retval = *m;
> > +       if (retval == old)
> > +               *m = new;
> > +       local_irq_restore(flags);
> > +       return (unsigned long)retval;
> > +}
> >  #endif /* __ASM_SH_CMPXCHG_IRQ_H */
> > diff --git a/arch/sh/include/asm/cmpxchg.h b/arch/sh/include/asm/cmpxchg.h
> > index e9501d85c278..7d65d0fd1665 100644
> > --- a/arch/sh/include/asm/cmpxchg.h
> > +++ b/arch/sh/include/asm/cmpxchg.h
> > @@ -56,8 +56,9 @@ static inline unsigned long __cmpxchg(volatile void * ptr, unsigned long old,
> >                 unsigned long new, int size)
> >  {
> >         switch (size) {
> > -       case 4:
> > -               return __cmpxchg_u32(ptr, old, new);
> > +       case 4: return __cmpxchg_u32((int *)ptr, old, new);
> > +       case 2: return __cmpxchg_u16((u16 *)ptr, old, new);
> > +       case 1: return __cmpxchg_u8((u8 *)ptr, old, new);
> >         }
> >         __cmpxchg_called_with_bad_pointer();
> >         return old;
>
> Gr{oetje,eeting}s,
>
> Geert
>
> --
> Geert Uytterhoeven -- There's lots of Linux beyond ia32 --
> geert@...ux-m68k.org
>
> In personal conversations with technical people, I call myself a hacker.
> But
> when I'm talking to journalists I just say "programmer" or something
> like that.
> -- Linus Torvalds

Thanks for your time,
Liam