On Wed, 25 Oct 2023 15:16:16 +0200
Geert Uytterhoeven [off-list ref] wrote:

Hi Adrian,

On Wed, Oct 25, 2023 at 12:32 PM John Paul Adrian Glaubitz
[off-list ref] wrote:

quoted

On Wed, 2023-10-25 at 11:30 +0100, Mark Rutland wrote:

quoted

On Wed, Oct 25, 2023 at 08:42:55AM +0900, Masami Hiramatsu wrote:

quoted

On Tue, 24 Oct 2023 16:08:12 +0100
Mark Rutland [off-list ref] wrote:

quoted

On Tue, Oct 24, 2023 at 11:52:54PM +0900, Masami Hiramatsu (Google) wrote:

quoted

From: Masami Hiramatsu (Google) <mhiramat@kernel.org>

Use generic_cmpxchg_local() for arch_cmpxchg_local() implementation
in SH architecture because it does not implement arch_cmpxchg_local().

I do not think this is correct.

The implementation in <asm-generic/cmpxchg-local.h> is UP-only (and it only
disables interrupts), whereas arch/sh can be built SMP. We should probably add
some guards into <asm-generic/cmpxchg-local.h> for that as we have in
<asm-generic/cmpxchg.h>.

Isn't cmpxchg_local for the data which only needs to ensure to do cmpxchg
on local CPU?
So I think it doesn't care about the other CPUs (IOW, it should not touched by
other CPUs), so it only considers UP case. E.g. on x86, arch_cmpxchg_local() is
defined as raw "cmpxchg" without lock prefix.

#define __cmpxchg_local(ptr, old, new, size)                            \
        __raw_cmpxchg((ptr), (old), (new), (size), "")

Yes, you're right; sorry for the noise.

For your original patch:

Acked-by: Mark Rutland <mark.rutland@arm.com>

Geert, what's your opinion on this?

While this looks OK on first sight (ARM includes the same file, even
on SMP), it does not seem to work?

For sh-allnoconfig, as reported by kernel test robot:

$ make ARCH=sh CROSS_COMPILE=sh2-linux- allnoconfig lib/objpool.o
lib/objpool.c: In function 'objpool_try_add_slot':
./include/linux/atomic/atomic-arch-fallback.h:384:27: error: implicit
declaration of function 'arch_cmpxchg_local'; did you mean
'raw_cmpxchg_local'? [-Werror=implicit-function-declaration]
  384 | #define raw_cmpxchg_local arch_cmpxchg_local
      |                           ^~~~~~~~~~~~~~~~~~
./include/linux/atomic/atomic-arch-fallback.h:392:16: note: in
expansion of macro 'raw_cmpxchg_local'
  392 |         ___r = raw_cmpxchg_local((_ptr), ___o, (_new)); \
      |                ^~~~~~~~~~~~~~~~~
./include/linux/atomic/atomic-instrumented.h:4980:9: note: in
expansion of macro 'raw_try_cmpxchg_local'
 4980 |         raw_try_cmpxchg_local(__ai_ptr, __ai_oldp, __VA_ARGS__); \
      |         ^~~~~~~~~~~~~~~~~~~~~
lib/objpool.c:169:19: note: in expansion of macro 'try_cmpxchg_local'
  169 |         } while (!try_cmpxchg_local(&slot->tail, &tail, tail + 1));
      |                   ^~~~~~~~~~~~~~~~~

For an SMP defconfig:

$ make ARCH=sh CROSS_COMPILE=sh4-linux-gnu- sdk7786_defconfig lib/objpool.o

./include/linux/atomic/atomic-arch-fallback.h:384:27: error: implicit
declaration of function ‘arch_cmpxchg_local’; did you mean
‘try_cmpxchg_local’? [-Werror=implicit-function-declaration]
  384 | #define raw_cmpxchg_local arch_cmpxchg_local
      |                           ^~~~~~~~~~~~~~~~~~
./include/linux/atomic/atomic-arch-fallback.h:392:16: note: in
expansion of macro ‘raw_cmpxchg_local’
  392 |         ___r = raw_cmpxchg_local((_ptr), ___o, (_new)); \
      |                ^~~~~~~~~~~~~~~~~
./include/linux/atomic/atomic-instrumented.h:4980:9: note: in
expansion of macro ‘raw_try_cmpxchg_local’
 4980 |         raw_try_cmpxchg_local(__ai_ptr, __ai_oldp, __VA_ARGS__); \
      |         ^~~~~~~~~~~~~~~~~~~~~
lib/objpool.c:169:19: note: in expansion of macro ‘try_cmpxchg_local’
  169 |         } while (!try_cmpxchg_local(&slot->tail, &tail, tail + 1));
      |                   ^~~~~~~~~~~~~~~~~

Hiramatsu-san: do these build for you?

Thanks for pointing. I thought I just need to include the header file.
That's my fault.

Let me fix that.

Thank you!

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-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

-- 
Masami Hiramatsu (Google) [off-list ref]