linux-kernel - Re: [RFC PATCH V3 31/43] rv64ilp32_abi: maple_tree: Use BITS_PER_LONG instead of CONFIG

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Message-ID: <CAJF2gTSR+jh04BT7rCjALL6eWek=VWm7nFTW57vzwshkTbrtVg@mail.gmail.com>
Date: Thu, 27 Mar 2025 20:47:15 +0800
From: Guo Ren <guoren@...nel.org>
To: "Liam R. Howlett" <Liam.Howlett@...cle.com>, guoren@...nel.org, arnd@...db.de, 
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Subject: Re: [RFC PATCH V3 31/43] rv64ilp32_abi: maple_tree: Use BITS_PER_LONG
 instead of CONFIG_64BIT

On Wed, Mar 26, 2025 at 3:10 AM Liam R. Howlett <Liam.Howlett@...cle.com> wrote:
>
> * guoren@...nel.org <guoren@...nel.org> [250325 08:24]:
> > From: "Guo Ren (Alibaba DAMO Academy)" <guoren@...nel.org>
> >
> > The Maple tree algorithm uses ulong type for each element. The
> > number of slots is based on BITS_PER_LONG for RV64ILP32 ABI, so
> > use BITS_PER_LONG instead of CONFIG_64BIT.
> >
> > Signed-off-by: Guo Ren (Alibaba DAMO Academy) <guoren@...nel.org>
> > ---
> >  include/linux/maple_tree.h | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/include/linux/maple_tree.h b/include/linux/maple_tree.h
> > index cbbcd18d4186..ff6265b6468b 100644
> > --- a/include/linux/maple_tree.h
> > +++ b/include/linux/maple_tree.h
> > @@ -24,7 +24,7 @@
> >   *
> >   * Nodes in the tree point to their parent unless bit 0 is set.
> >   */
> > -#if defined(CONFIG_64BIT) || defined(BUILD_VDSO32_64)
> > +#if (BITS_PER_LONG == 64) || defined(BUILD_VDSO32_64)
>
> This will break my userspace testing, if you do not update the testing as
> well.  This can be found in tools/testing/radix-tree.  Please also look
> at the Makefile as well since it will generate a build flag for the
> userspace.
I think you are talking about the following:
============================================================
../shared/shared.mk:
ifndef LONG_BIT
LONG_BIT := $(shell getconf LONG_BIT)
endif

generated/bit-length.h: FORCE
        @mkdir -p generated
        @if ! grep -qws CONFIG_$(LONG_BIT)BIT generated/bit-length.h; then   \
                echo "Generating $@";                                        \
                echo "#define CONFIG_$(LONG_BIT)BIT 1" > $@;                 \
                echo "#define CONFIG_PHYS_ADDR_T_$(LONG_BIT)BIT 1" >> $@;    \
        fi

$ grep CONFIG_64BIT * -r -A 2
generated/bit-length.h:#define CONFIG_64BIT 1
generated/bit-length.h-#define CONFIG_PHYS_ADDR_T_64BIT 1
--
maple.c:#if defined(CONFIG_64BIT)
maple.c-static noinline void __init check_erase2_testset(struct maple_tree *mt,
maple.c-                const unsigned long *set, unsigned long size)
--
maple.c:#if CONFIG_64BIT
maple.c-        MT_BUG_ON(mt, data_end != mas_data_end(&mas));
maple.c-#endif
--
maple.c:#if CONFIG_64BIT
maple.c-        MT_BUG_ON(mt, data_end - 2 != mas_data_end(&mas));
maple.c-#endif
--
maple.c:#if CONFIG_64BIT
maple.c-        MT_BUG_ON(mt, data_end - 4 != mas_data_end(&mas));
maple.c-#endif
--
maple.c:#if defined(CONFIG_64BIT)
maple.c-        /* Captures from VMs that found previous errors */
maple.c-        mt_init_flags(&tree, 0);
============================================================

First, we don't introduce rv64ilp32-abi user space, which means these
testing codes can't run on rv64ilp32-abi userspace currently. So, the
problem you mentioned doesn't exist.

Second, CONFIG_32BIT is determined by LONG_BIT, so there's no issue in
maple.c with future rv64ilp32-abi userspace.
That means rv64ilp32-abi userspace would use CONFIG_32BIT to test
radix-tree. It's okay.

>
> This raises other concerns as the code is found with a grep command, so
> I'm not sure why it was missed and if anything else is missed?
>
> If you consider this email to be the (unasked) question about what to do
> here, then please CC me, the maintainer of the files including the one
> you are updating here.
>
> Thank you,
> Liam
>


-- 
Best Regards
 Guo Ren