[paulmckrcu:cmpxchg2.2026.09.22a 25/28] arch/arc/include/asm/cmpxchg.h:71:23: warning: unused variable '_new_'
Paul E. McKenney
paulmck at kernel.org
Wed Sep 23 20:25:18 PDT 2026
On Wed, Sep 23, 2026 at 03:23:47PM -0700, Vineet Gupta wrote:
> On 9/23/26 14:13, Bradley Morgan wrote:
> > On 23 September 2026 22:12:09 BST, kernel test robot <lkp at intel.com> wrote:
> > > tree: https://github.com/paulmckrcu/linux cmpxchg2.2026.09.22a
> > > head: 54c282c15475ebfae4712fe3ab637c9d19c723d6
> > > commit: b6d4f6af38f85e7948fd64f9bf09cbb858b4dade [25/28] ARC: Emulate two-byte cmpxchg
> > > config: arc-randconfig-1001-20260924 (https://download.01.org/0day-ci/archive/20260924/202609240539.AkulvjVe-lkp@intel.com/config)
> > > compiler: arc-linux-gcc (GCC) 14.3.0
> > > reproduce (this is a W=1 build):
> > > (https://download.01.org/0day-ci/archive/20260924/202609240539.AkulvjVe-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 at intel.com>
> > > | Closes:
> > > https://lore.kernel.org/oe-kbuild-all/202609240539.AkulvjVe-lkp@intel.com/
> > >
> > > All warnings (new ones prefixed by >>):
> > >
> > > In file included from arch/arc/include/asm/atomic.h:13,
> > > from include/linux/atomic.h:7,
> > > from include/asm-generic/bitops/lock.h:5,
> > > from arch/arc/include/asm/bitops.h:190,
> > > from include/linux/bitops.h:67,
> > > from include/linux/log2.h:12,
> > > from kernel/bounds.c:14:
> > > include/linux/atomic/atomic-arch-fallback.h: In function 'raw_atomic_cmpxchg':
> > > arch/arc/include/asm/cmpxchg.h:80:23: error: '_o_' undeclared (first use in this function); did you mean '_p_'?
> > > 80 | if (_prev_ == _o_) \
> > > | ^~~
> > > include/linux/atomic/atomic-arch-fallback.h:55:21: note: in expansion of macro 'arch_cmpxchg'
> > > 55 | #define raw_cmpxchg arch_cmpxchg
> > > | ^~~~~~~~~~~~
> > > include/linux/atomic/atomic-arch-fallback.h:2026:16: note: in expansion of macro 'raw_cmpxchg'
> > > 2026 | return raw_cmpxchg(&v->counter, old, new);
> > > | ^~~~~~~~~~~
> > > arch/arc/include/asm/cmpxchg.h:80:23: note: each undeclared identifier is reported only once for each function it appears in
> > > 80 | if (_prev_ == _o_) \
> > > | ^~~
> > > include/linux/atomic/atomic-arch-fallback.h:55:21: note: in expansion of macro 'arch_cmpxchg'
> > > 55 | #define raw_cmpxchg arch_cmpxchg
> > > | ^~~~~~~~~~~~
> > > include/linux/atomic/atomic-arch-fallback.h:2026:16: note: in expansion of macro 'raw_cmpxchg'
> > > 2026 | return raw_cmpxchg(&v->counter, old, new);
> > > | ^~~~~~~~~~~
> > > arch/arc/include/asm/cmpxchg.h:81:24: error: '_n_' undeclared (first use in this function); did you mean '_p_'?
> > > 81 | *_p_ = _n_; \
> > > | ^~~
> > > include/linux/atomic/atomic-arch-fallback.h:55:21: note: in expansion of macro 'arch_cmpxchg'
> > > 55 | #define raw_cmpxchg arch_cmpxchg
> > > | ^~~~~~~~~~~~
> > > include/linux/atomic/atomic-arch-fallback.h:2026:16: note: in expansion of macro 'raw_cmpxchg'
> > > 2026 | return raw_cmpxchg(&v->counter, old, new);
> > > | ^~~~~~~~~~~
> > > > > arch/arc/include/asm/cmpxchg.h:71:23: warning: unused variable '_new_'
> > > [-Wunused-variable]
> > > 71 | unsigned long _new_ = (unsigned long)(0 ? *(_p_) : (new)); \
> > > | ^~~~~
> > > include/linux/atomic/atomic-arch-fallback.h:55:21: note: in expansion of macro 'arch_cmpxchg'
> > > 55 | #define raw_cmpxchg arch_cmpxchg
> > > | ^~~~~~~~~~~~
> > > include/linux/atomic/atomic-arch-fallback.h:2026:16: note: in expansion of macro 'raw_cmpxchg'
> > > 2026 | return raw_cmpxchg(&v->counter, old, new);
> > > | ^~~~~~~~~~~
> > > > > arch/arc/include/asm/cmpxchg.h:70:23: warning: unused variable '_old_'
> > > [-Wunused-variable]
> > > 70 | unsigned long _old_ = (unsigned long)(0 ? *(_p_) : (old)); \
> > > | ^~~~~
> > > include/linux/atomic/atomic-arch-fallback.h:55:21: note: in expansion of macro 'arch_cmpxchg'
> > > 55 | #define raw_cmpxchg arch_cmpxchg
> > > | ^~~~~~~~~~~~
> > > include/linux/atomic/atomic-arch-fallback.h:2026:16: note: in expansion of macro 'raw_cmpxchg'
> > > 2026 | return raw_cmpxchg(&v->counter, old, new);
> > > | ^~~~~~~~~~~
> > > include/linux/atomic/atomic-arch-fallback.h: In function 'raw_atomic_cmpxchg_acquire':
> > > arch/arc/include/asm/cmpxchg.h:80:23: error: '_o_' undeclared (first use in this function); did you mean '_p_'?
> > > 80 | if (_prev_ == _o_) \
> > > | ^~~
> > > include/linux/atomic/atomic-arch-fallback.h:70:29: note: in expansion of macro 'arch_cmpxchg'
> > > 70 | #define raw_cmpxchg_acquire arch_cmpxchg
> > > | ^~~~~~~~~~~~
> > > include/linux/atomic/atomic-arch-fallback.h:2055:16: note: in expansion of macro 'raw_cmpxchg_acquire'
> > > 2055 | return raw_cmpxchg_acquire(&v->counter, old, new);
> > > | ^~~~~~~~~~~~~~~~~~~
> > > arch/arc/include/asm/cmpxchg.h:81:24: error: '_n_' undeclared (first use in this function); did you mean '_p_'?
> > > 81 | *_p_ = _n_; \
> > > | ^~~
> > > include/linux/atomic/atomic-arch-fallback.h:70:29: note: in expansion of macro 'arch_cmpxchg'
> > > 70 | #define raw_cmpxchg_acquire arch_cmpxchg
> > > | ^~~~~~~~~~~~
> > > include/linux/atomic/atomic-arch-fallback.h:2055:16: note: in expansion of macro 'raw_cmpxchg_acquire'
> > > 2055 | return raw_cmpxchg_acquire(&v->counter, old, new);
> > > | ^~~~~~~~~~~~~~~~~~~
> > > > > arch/arc/include/asm/cmpxchg.h:71:23: warning: unused variable '_new_'
> > > [-Wunused-variable]
> > > 71 | unsigned long _new_ = (unsigned long)(0 ? *(_p_) : (new)); \
> > > | ^~~~~
> > > include/linux/atomic/atomic-arch-fallback.h:70:29: note: in expansion of macro 'arch_cmpxchg'
> > > 70 | #define raw_cmpxchg_acquire arch_cmpxchg
> > > | ^~~~~~~~~~~~
> > > include/linux/atomic/atomic-arch-fallback.h:2055:16: note: in expansion of macro 'raw_cmpxchg_acquire'
> > > 2055 | return raw_cmpxchg_acquire(&v->counter, old, new);
> > > | ^~~~~~~~~~~~~~~~~~~
> > > > > arch/arc/include/asm/cmpxchg.h:70:23: warning: unused variable '_old_'
> > > [-Wunused-variable]
> > > 70 | unsigned long _old_ = (unsigned long)(0 ? *(_p_) : (old)); \
> > > | ^~~~~
> > > include/linux/atomic/atomic-arch-fallback.h:70:29: note: in expansion of macro 'arch_cmpxchg'
> > > 70 | #define raw_cmpxchg_acquire arch_cmpxchg
> > > | ^~~~~~~~~~~~
> > > include/linux/atomic/atomic-arch-fallback.h:2055:16: note: in expansion of macro 'raw_cmpxchg_acquire'
> > > 2055 | return raw_cmpxchg_acquire(&v->counter, old, new);
> > > | ^~~~~~~~~~~~~~~~~~~
> > > include/linux/atomic/atomic-arch-fallback.h: In function 'raw_atomic_cmpxchg_release':
> > > arch/arc/include/asm/cmpxchg.h:80:23: error: '_o_' undeclared (first use in this function); did you mean '_p_'?
> > > 80 | if (_prev_ == _o_) \
> > > | ^~~
> > > include/linux/atomic/atomic-arch-fallback.h:82:29: note: in expansion of macro 'arch_cmpxchg'
> > > 82 | #define raw_cmpxchg_release arch_cmpxchg
> > > | ^~~~~~~~~~~~
> > > include/linux/atomic/atomic-arch-fallback.h:2083:16: note: in expansion of macro 'raw_cmpxchg_release'
> > > 2083 | return raw_cmpxchg_release(&v->counter, old, new);
> > > | ^~~~~~~~~~~~~~~~~~~
> > > arch/arc/include/asm/cmpxchg.h:81:24: error: '_n_' undeclared (first use in this function); did you mean '_p_'?
> > > 81 | *_p_ = _n_; \
> > > | ^~~
> > > include/linux/atomic/atomic-arch-fallback.h:82:29: note: in expansion of macro 'arch_cmpxchg'
> > > 82 | #define raw_cmpxchg_release arch_cmpxchg
> > > | ^~~~~~~~~~~~
> > > include/linux/atomic/atomic-arch-fallback.h:2083:16: note: in expansion of macro 'raw_cmpxchg_release'
> > > 2083 | return raw_cmpxchg_release(&v->counter, old, new);
> > > | ^~~~~~~~~~~~~~~~~~~
> > > > > arch/arc/include/asm/cmpxchg.h:71:23: warning: unused variable '_new_'
> > > [-Wunused-variable]
> > > 71 | unsigned long _new_ = (unsigned long)(0 ? *(_p_) : (new)); \
> > > | ^~~~~
> > > include/linux/atomic/atomic-arch-fallback.h:82:29: note: in expansion of macro 'arch_cmpxchg'
> > > 82 | #define raw_cmpxchg_release arch_cmpxchg
> > > | ^~~~~~~~~~~~
> > > include/linux/atomic/atomic-arch-fallback.h:2083:16: note: in expansion of macro 'raw_cmpxchg_release'
> > > 2083 | return raw_cmpxchg_release(&v->counter, old, new);
> > > | ^~~~~~~~~~~~~~~~~~~
> > > > > arch/arc/include/asm/cmpxchg.h:70:23: warning: unused variable '_old_'
> > > [-Wunused-variable]
> > > 70 | unsigned long _old_ = (unsigned long)(0 ? *(_p_) : (old)); \
> > > | ^~~~~
> > > include/linux/atomic/atomic-arch-fallback.h:82:29: note: in expansion of macro 'arch_cmpxchg'
> > > 82 | #define raw_cmpxchg_release arch_cmpxchg
> > > | ^~~~~~~~~~~~
> > > include/linux/atomic/atomic-arch-fallback.h:2083:16: note: in expansion of macro 'raw_cmpxchg_release'
> > > 2083 | return raw_cmpxchg_release(&v->counter, old, new);
> > > | ^~~~~~~~~~~~~~~~~~~
> > > include/linux/atomic/atomic-arch-fallback.h: In function 'raw_atomic_cmpxchg_relaxed':
> > > arch/arc/include/asm/cmpxchg.h:80:23: error: '_o_' undeclared (first use in this function); did you mean '_p_'?
> > > 80 | if (_prev_ == _o_) \
> > > | ^~~
> > > include/linux/atomic/atomic-arch-fallback.h:91:29: note: in expansion of macro 'arch_cmpxchg'
> > > 91 | #define raw_cmpxchg_relaxed arch_cmpxchg
> > > | ^~~~~~~~~~~~
> > > include/linux/atomic/atomic-arch-fallback.h:2108:16: note: in expansion of macro 'raw_cmpxchg_relaxed'
> > > 2108 | return raw_cmpxchg_relaxed(&v->counter, old, new);
> > > | ^~~~~~~~~~~~~~~~~~~
> > > arch/arc/include/asm/cmpxchg.h:81:24: error: '_n_' undeclared (first use in this function); did you mean '_p_'?
> > > 81 | *_p_ = _n_; \
> > > | ^~~
> > > include/linux/atomic/atomic-arch-fallback.h:91:29: note: in expansion of macro 'arch_cmpxchg'
> > > 91 | #define raw_cmpxchg_relaxed arch_cmpxchg
> > > | ^~~~~~~~~~~~
> > > include/linux/atomic/atomic-arch-fallback.h:2108:16: note: in expansion of macro 'raw_cmpxchg_relaxed'
> > > 2108 | return raw_cmpxchg_relaxed(&v->counter, old, new);
> > > | ^~~~~~~~~~~~~~~~~~~
> > > > > arch/arc/include/asm/cmpxchg.h:71:23: warning: unused variable '_new_'
> > > [-Wunused-variable]
> > > 71 | unsigned long _new_ = (unsigned long)(0 ? *(_p_) : (new)); \
> > > | ^~~~~
> > > include/linux/atomic/atomic-arch-fallback.h:91:29: note: in expansion of macro 'arch_cmpxchg'
> > > 91 | #define raw_cmpxchg_relaxed arch_cmpxchg
> > > | ^~~~~~~~~~~~
> > > include/linux/atomic/atomic-arch-fallback.h:2108:16: note: in expansion of macro 'raw_cmpxchg_relaxed'
> > > 2108 | return raw_cmpxchg_relaxed(&v->counter, old, new);
> > > | ^~~~~~~~~~~~~~~~~~~
> > > > > arch/arc/include/asm/cmpxchg.h:70:23: warning: unused variable '_old_'
> > > [-Wunused-variable]
> > > 70 | unsigned long _old_ = (unsigned long)(0 ? *(_p_) : (old)); \
> > > | ^~~~~
> > > include/linux/atomic/atomic-arch-fallback.h:91:29: note: in expansion of macro 'arch_cmpxchg'
> > > 91 | #define raw_cmpxchg_relaxed arch_cmpxchg
> > > | ^~~~~~~~~~~~
> > > include/linux/atomic/atomic-arch-fallback.h:2108:16: note: in expansion of macro 'raw_cmpxchg_relaxed'
> > > 2108 | return raw_cmpxchg_relaxed(&v->counter, old, new);
> > > | ^~~~~~~~~~~~~~~~~~~
> > > make[3]: *** [scripts/Makefile.build:185: kernel/bounds.s] Error 1 shuffle=1050985161
> > > make[3]: Target 'prepare' not remade because of errors.
> > > make[2]: *** [Makefile:1425: prepare0] Error 2 shuffle=1050985161
> > > make[2]: Target 'prepare' not remade because of errors.
> > > make[1]: *** [Makefile:248: __sub-make] Error 2 shuffle=1050985161
> > > make[1]: Target 'prepare' not remade because of errors.
> > > make: *** [Makefile:248: __sub-make] Error 2 shuffle=1050985161
> > > make: Target 'prepare' not remade because of errors.
> > >
> > >
> > > vim +/_new_ +71 arch/arc/include/asm/cmpxchg.h
> > >
> > > 66
> > > 67 #define arch_cmpxchg(ptr, old, new) \
> > > 68 ({ \
> > > 69 volatile __typeof__(ptr) _p_ = (ptr); \
> > > > 70 unsigned long _old_ = (unsigned long)(0 ? *(_p_) : (old)); \
> > > > 71 unsigned long _new_ = (unsigned long)(0 ? *(_p_) : (new)); \
> > > 72 __typeof__(*(ptr)) _prev_; \
> > > 73 unsigned long __flags; \
> > > 74 \
> > > 75 /* \
> > > 76 * spin lock/unlock provide the needed smp_mb() before/after \
> > > 77 */ \
> > > 78 atomic_ops_lock(__flags); \
> > > 79 _prev_ = *_p_; \
> > > 80 if (_prev_ == _o_) \
> > > 81 *_p_ = _n_; \
> > > 82 atomic_ops_unlock(__flags); \
> > > 83 _prev_; \
> > > 84 })
> > > 85
> > >
> > > --
> > > 0-DAY CI Kernel Test Service
> > > https://github.com/intel/lkp-tests/wiki
> > Apparently nobody uses arc
>
> Yes the development has slowed down compared to five years ago, but its not
> dead, if anything it is still my hobby project, like so many other things
> open source and you repeating this hurts.
>
> You stumbled onto a real issue: typeof ptr vs. *ptr which unmasked an
> existing shortcoming.
> @Paul can you please apply this in your tree and rebase the series on top.
> If not I can send this fix to Linus urgently, but it will cause some
> collisions.
Thank you, Vineet!
Just to make sure I understand, I apply this patch, then Bradley sends
me an updated version of his patch, which I apply on top of yours.
Just double-checking. ;-)
Thanx, Paul
> ---------->
> From f3e2402f62bebfa9f1ad21e23d1663a0a3e5a58d Mon Sep 17 00:00:00 2001
> From: Vineet Gupta <vgupta at kernel.org>
> Date: Wed, 23 Sep 2026 15:01:38 -0700
> Subject: [PATCH] ARC: arch_cmpxchg_relaxed to use size of pointed type not
> pointer
>
> Bradley spotted this snafu when working on two-byte cmpxchg emulation.
> He originally folded this fix into his series but the fix itself
> uncovered a pre-existing issue, missing arch_atomic64_cmpxchg_relaxed
> which just needed to be wired up.
>
> Fixes: e188f3330a13 ("ARC: cmpxchg/xchg: rewrite as macros to make type
> safe")
> Reported-by: kernel test robot <lkp at intel.com>
> Closes:
> https://lore.kernel.org/oe-kbuild-all/202609240539.AkulvjVe-lkp@intel.com/
> Suggested-by: Bradley Morgan <brads at mainlining.org>
> Signed-off-by: Vineet Gupta <vgupta at kernel.org>
> ---
> arch/arc/include/asm/atomic64-arcv2.h | 6 ++++++
> arch/arc/include/asm/cmpxchg.h | 4 ++--
> 2 files changed, 8 insertions(+), 2 deletions(-)
>
> diff --git a/arch/arc/include/asm/atomic64-arcv2.h
> b/arch/arc/include/asm/atomic64-arcv2.h
> index 73080a664369..1ca4a1047fb3 100644
> --- a/arch/arc/include/asm/atomic64-arcv2.h
> +++ b/arch/arc/include/asm/atomic64-arcv2.h
> @@ -156,6 +156,12 @@ static inline u64 __arch_cmpxchg64_relaxed(volatile
> void *ptr, u64 old, u64 new)
> }
> #define arch_cmpxchg64_relaxed __arch_cmpxchg64_relaxed
>
> +static inline s64 arch_atomic64_cmpxchg_relaxed(atomic64_t *v, s64 old, s64
> new)
> +{
> + return arch_cmpxchg64_relaxed(&v->counter, old, new);
> +}
> +#define arch_atomic64_cmpxchg_relaxed arch_atomic64_cmpxchg_relaxed
> +
> static inline s64 arch_atomic64_xchg(atomic64_t *ptr, s64 new)
> {
> s64 prev;
> diff --git a/arch/arc/include/asm/cmpxchg.h b/arch/arc/include/asm/cmpxchg.h
> index 76f43db0890f..66b3743c9400 100644
> --- a/arch/arc/include/asm/cmpxchg.h
> +++ b/arch/arc/include/asm/cmpxchg.h
> @@ -46,7 +46,7 @@
> __typeof__(*(ptr)) _n_ = (new); \
> __typeof__(*(ptr)) _prev_; \
> \
> - switch(sizeof((_p_))) { \
> + switch (sizeof(*(_p_))) { \
> case 1: \
> _prev_ = (__typeof__(*(ptr)))cmpxchg_emu_u8((volatile u8
> *__force)_p_, (uintptr_t)_o_, (uintptr_t)_n_); \
> break; \
> @@ -102,7 +102,7 @@
> __typeof__(ptr) _p_ = (ptr); \
> __typeof__(*(ptr)) _val_ = (val); \
> \
> - switch(sizeof(*(_p_))) { \
> + switch (sizeof(*(_p_))) { \
> case 4: \
> _val_ = __arch_xchg(_p_, _val_); \
> break; \
> --
> 2.53.0
>
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