Re: [boqun:rust-sync.20260105a 18/22] error[E0277]: the trait bound `i8: AtomicImpl` is not satisfied

Re: [boqun:rust-sync.20260105a 18/22] error[E0277]: the trait bound `i8: AtomicImpl` is not satisfied

[Boqun Feng]

[Cc UML]

On Tue, Jan 06, 2026 at 12:25:24AM +0800, kernel test robot wrote:
> tree:   https://git.kernel.org/pub/scm/linux/kernel/git/boqun/linux.git rust-sync.20260105a
> head:   243aa6a057d46d3a4de9297422e480d469eddaf7
> commit: 06ed7e7e7aa656f7054af7d3d3387a07244d85b1 [18/22] rust: sync: atomic: Add i8/i16 xchg and cmpxchg support
> config: um-randconfig-001-20260105 (https://download.01.org/0day-ci/archive/20260106/202601060041.k0JkAkUD-lkp@intel.com/config)
> compiler: clang version 22.0.0git (https://github.com/llvm/llvm-project 9b8addffa70cee5b2acc5454712d9cf78ce45710)
> rustc: rustc 1.88.0 (6b00bc388 2025-06-23)
> reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20260106/202601060041.k0JkAkUD-lkp@intel.com/reproduce)
> 
> If you fix the issue in a separate patch/commit (i.e. not just a new version of
> the same patch/commit), kindly add following tags
> | Reported-by: kernel test robot <lkp@intel.com>
> | Closes: https://lore.kernel.org/oe-kbuild-all/202601060041.k0JkAkUD-lkp@intel.com/
> 
> All errors (new ones prefixed by >>):
> 
>    In file included from kernel/sched/rq-offsets.c:5:
>    In file included from kernel/sched/sched.h:28:
>    In file included from include/linux/cgroup_api.h:1:
>    In file included from include/linux/cgroup.h:27:
>    In file included from include/linux/kernel_stat.h:8:
>    In file included from include/linux/interrupt.h:11:
>    In file included from include/linux/hardirq.h:11:
>    In file included from arch/um/include/asm/hardirq.h:24:
>    In file included from include/linux/irq.h:20:
>    In file included from include/linux/io.h:12:
>    In file included from arch/um/include/asm/io.h:24:
>    include/asm-generic/io.h:1209:55: warning: performing pointer arithmetic on a null pointer has undefined behavior [-Wnull-pointer-arithmetic]
>    1209 |         return (port > MMIO_UPPER_LIMIT) ? NULL : PCI_IOBASE + port;
>    |                                                   ~~~~~~~~~~ ^
>    1 warning generated.
>    llvm-nm: error: rust/helpers/helpers.o: No such file or directory
>    clang diag: include/asm-generic/io.h:1209:55: warning: performing pointer arithmetic on a null pointer has undefined behavior [-Wnull-pointer-arithmetic]
>    clang diag: include/asm-generic/io.h:1209:55: warning: performing pointer arithmetic on a null pointer has undefined behavior [-Wnull-pointer-arithmetic]
>    clang diag: include/asm-generic/io.h:1209:55: warning: performing pointer arithmetic on a null pointer has undefined behavior [-Wnull-pointer-arithmetic]
> >> error[E0277]: the trait bound `i8: AtomicImpl` is not satisfied
>    --> rust/kernel/sync/atomic/internal.rs:265:7
>    |
>    265 |     [ i8 => atomic_i8, i16 => atomic_i16, i32 => atomic, i64 => atomic64 ]
>    |       ^^ the trait `AtomicImpl` is not implemented for `i8`
>    |
>    = help: the following other types implement trait `AtomicImpl`:
>    i32
>    i64

UML_X86 is using the atomics of x86 kernel (defined in
arch/x86/include/asm/atomic*), right? If so, I think we need this:

diff --git a/arch/x86/um/Kconfig b/arch/x86/um/Kconfig
index bdd7c8e39b01..44b12e45f9a0 100644
--- a/arch/x86/um/Kconfig
+++ b/arch/x86/um/Kconfig
@@ -9,6 +9,7 @@ endmenu
 config UML_X86
        def_bool y
        select ARCH_USE_QUEUED_RWLOCKS
+       select ARCH_SUPPORTS_ATOMIC_RMW
        select ARCH_USE_QUEUED_SPINLOCKS
        select DCACHE_WORD_ACCESS
        select HAVE_EFFICIENT_UNALIGNED_ACCESS

Regards,
Boqun

[...]

[PATCH] arch: um/x86: Select ARCH_SUPPORTS_ATOMIC_RMW for UML_X86

[Boqun Feng]

x86 atomic instructions are used for um on UML_X86, therefore atomics
on UML_X86 support native atomic RmW as x86 does, hence select
ARCH_SUPPORTS_ATOMIC_RMW.

Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
---
UM & x86 maintainers,

I need this to avoid a build error for Rust atomics since Rust currently
only support Atomic<i8/i16> on ARCH_SUPPORTS_ATOMIC_RMW archs. I will
add it to my upcoming PR if I get some Acked-by, thanks!

 arch/x86/um/Kconfig | 1 +
 1 file changed, 1 insertion(+)

diff --git a/arch/x86/um/Kconfig b/arch/x86/um/Kconfig
index bdd7c8e39b01..44b12e45f9a0 100644
--- a/arch/x86/um/Kconfig
+++ b/arch/x86/um/Kconfig
@@ -9,6 +9,7 @@ endmenu
 config UML_X86
 	def_bool y
 	select ARCH_USE_QUEUED_RWLOCKS
+	select ARCH_SUPPORTS_ATOMIC_RMW
 	select ARCH_USE_QUEUED_SPINLOCKS
 	select DCACHE_WORD_ACCESS
 	select HAVE_EFFICIENT_UNALIGNED_ACCESS
-- 
2.51.0

Re: [PATCH] arch: um/x86: Select ARCH_SUPPORTS_ATOMIC_RMW for UML_X86

[FUJITA Tomonori]

On Tue,  6 Jan 2026 11:40:34 +0800
Boqun Feng <boqun.feng@gmail.com> wrote:

> x86 atomic instructions are used for um on UML_X86, therefore atomics
> on UML_X86 support native atomic RmW as x86 does, hence select
> ARCH_SUPPORTS_ATOMIC_RMW.
> 
> Signed-off-by: Boqun Feng <boqun.feng@gmail.com>

Reviewed-by: FUJITA Tomonori <fujita.tomonori@gmail.com>

Re: [PATCH] arch: um/x86: Select ARCH_SUPPORTS_ATOMIC_RMW for UML_X86

[Richard Weinberger]

----- Ursprüngliche Mail -----
> Von: "Boqun Feng" <boqun.feng@gmail.com>
> An: "linux-um" <linux-um@lists.infradead.org>, "x86" <x86@kernel.org>
> CC: "richard" <richard@nod.at>, "anton ivanov" <anton.ivanov@cambridgegreys.com>, "Johannes Berg"
> <johannes@sipsolutions.net>, "tglx" <tglx@linutronix.de>, "mingo" <mingo@redhat.com>, "bp" <bp@alien8.de>, "dave
> hansen" <dave.hansen@linux.intel.com>, "hpa" <hpa@zytor.com>, "Miguel Ojeda" <ojeda@kernel.org>, "Boqun Feng"
> <boqun.feng@gmail.com>, "Gary Guo" <gary@garyguo.net>, "Björn Roy Baron" <bjorn3_gh@protonmail.com>, "Benno Lossin"
> <lossin@kernel.org>, "Andreas Hindborg" <a.hindborg@kernel.org>, "Alice Ryhl" <aliceryhl@google.com>, "Trevor Gross"
> <tmgross@umich.edu>, "dakr" <dakr@kernel.org>, "linux-kernel" <linux-kernel@vger.kernel.org>, "Rust for Linux Kernel"
> <rust-for-linux@vger.kernel.org>, "FUJITA Tomonori" <fujita.tomonori@gmail.com>
> Gesendet: Dienstag, 6. Januar 2026 04:40:34
> Betreff: [PATCH] arch: um/x86: Select ARCH_SUPPORTS_ATOMIC_RMW for UML_X86

> x86 atomic instructions are used for um on UML_X86, therefore atomics
> on UML_X86 support native atomic RmW as x86 does, hence select
> ARCH_SUPPORTS_ATOMIC_RMW.
> 
> Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
> ---
> UM & x86 maintainers,
> 
> I need this to avoid a build error for Rust atomics since Rust currently
> only support Atomic<i8/i16> on ARCH_SUPPORTS_ATOMIC_RMW archs. I will
> add it to my upcoming PR if I get some Acked-by, thanks!
> 
> arch/x86/um/Kconfig | 1 +
> 1 file changed, 1 insertion(+)

Acked-by: Richard Weinberger <richard@nod.at>

Thanks,
//richard

Re: [PATCH] arch: um/x86: Select ARCH_SUPPORTS_ATOMIC_RMW for UML_X86

[Boqun Feng]

On Tue, Jan 06, 2026 at 03:20:43PM +0100, Richard Weinberger wrote:
> ----- Ursprüngliche Mail -----
> > Von: "Boqun Feng" <boqun.feng@gmail.com>
> > An: "linux-um" <linux-um@lists.infradead.org>, "x86" <x86@kernel.org>
> > CC: "richard" <richard@nod.at>, "anton ivanov" <anton.ivanov@cambridgegreys.com>, "Johannes Berg"
> > <johannes@sipsolutions.net>, "tglx" <tglx@linutronix.de>, "mingo" <mingo@redhat.com>, "bp" <bp@alien8.de>, "dave
> > hansen" <dave.hansen@linux.intel.com>, "hpa" <hpa@zytor.com>, "Miguel Ojeda" <ojeda@kernel.org>, "Boqun Feng"
> > <boqun.feng@gmail.com>, "Gary Guo" <gary@garyguo.net>, "Björn Roy Baron" <bjorn3_gh@protonmail.com>, "Benno Lossin"
> > <lossin@kernel.org>, "Andreas Hindborg" <a.hindborg@kernel.org>, "Alice Ryhl" <aliceryhl@google.com>, "Trevor Gross"
> > <tmgross@umich.edu>, "dakr" <dakr@kernel.org>, "linux-kernel" <linux-kernel@vger.kernel.org>, "Rust for Linux Kernel"
> > <rust-for-linux@vger.kernel.org>, "FUJITA Tomonori" <fujita.tomonori@gmail.com>
> > Gesendet: Dienstag, 6. Januar 2026 04:40:34
> > Betreff: [PATCH] arch: um/x86: Select ARCH_SUPPORTS_ATOMIC_RMW for UML_X86
> 
> > x86 atomic instructions are used for um on UML_X86, therefore atomics
> > on UML_X86 support native atomic RmW as x86 does, hence select
> > ARCH_SUPPORTS_ATOMIC_RMW.
> > 
> > Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
> > ---
> > UM & x86 maintainers,
> > 
> > I need this to avoid a build error for Rust atomics since Rust currently
> > only support Atomic<i8/i16> on ARCH_SUPPORTS_ATOMIC_RMW archs. I will
> > add it to my upcoming PR if I get some Acked-by, thanks!
> > 
> > arch/x86/um/Kconfig | 1 +
> > 1 file changed, 1 insertion(+)
> 
> Acked-by: Richard Weinberger <richard@nod.at>
> 

Queued with both tags applied, thank you both!

Regards,
Boqun

> Thanks,
> //richard