[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 30 10:52:51 PDT 2026
On Tue, Sep 29, 2026 at 12:42:52PM -0700, Vineet Gupta wrote:
> On 9/29/26 12:16, Paul E. McKenney wrote:
> > 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.
> > I tried applying this against current linux/master, v7.2, and v7.3-rc1,
> > and no go. Please let me know what you based this on.
> >
> > Or is this in your recent pull request from Linus? In which case,
> > I could pull that and cherry-pick this patch.
>
> Its the latter.
Done!
Thanx, Paul
> Thx,
> -Vineet
>
> >
> > 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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