ARC: Use __force to suppress per-CPU cmpxchg complaints

Posted by Paul E. McKenney 1 month, 2 weeks ago

Currently, the cast of the first argument to cmpxchg_emu_u8() drops the
__percpu address-space designator, which results in sparse complaints
when applying cmpxchg() to per-CPU variables in ARC.  Therefore, use
__force to suppress these complaints, given that this does not pertain
to cmpxchg() semantics, which are plently well-defined on variables in
general, whether per-CPU or otherwise.

Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202409251336.ToC0TvWB-lkp@intel.com/
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Cc: Vineet Gupta <vgupta@kernel.org>
Cc: <linux-snps-arc@lists.infradead.org>

diff --git a/arch/arc/include/asm/cmpxchg.h b/arch/arc/include/asm/cmpxchg.h
index 58045c8983404..76f43db0890fc 100644
--- a/arch/arc/include/asm/cmpxchg.h
+++ b/arch/arc/include/asm/cmpxchg.h
@@ -48,7 +48,7 @@
 									\
 	switch(sizeof((_p_))) {						\
 	case 1:								\
-		_prev_ = (__typeof__(*(ptr)))cmpxchg_emu_u8((volatile u8 *)_p_, (uintptr_t)_o_, (uintptr_t)_n_);	\
+		_prev_ = (__typeof__(*(ptr)))cmpxchg_emu_u8((volatile u8 *__force)_p_, (uintptr_t)_o_, (uintptr_t)_n_);	\
 		break;							\
 	case 4:								\
 		_prev_ = __cmpxchg(_p_, _o_, _n_);			\

Re: ARC: Use __force to suppress per-CPU cmpxchg complaints

Posted by Vineet Gupta 1 month, 1 week ago

On 10/9/24 10:55, Paul E. McKenney wrote:
> Currently, the cast of the first argument to cmpxchg_emu_u8() drops the
> __percpu address-space designator, which results in sparse complaints
> when applying cmpxchg() to per-CPU variables in ARC.  Therefore, use
> __force to suppress these complaints, given that this does not pertain
> to cmpxchg() semantics, which are plently well-defined on variables in
> general, whether per-CPU or otherwise.
>
> Reported-by: kernel test robot <lkp@intel.com>
> Closes: https://lore.kernel.org/oe-kbuild-all/202409251336.ToC0TvWB-lkp@intel.com/
> Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
> Cc: Vineet Gupta <vgupta@kernel.org>
> Cc: <linux-snps-arc@lists.infradead.org>
>
> diff --git a/arch/arc/include/asm/cmpxchg.h b/arch/arc/include/asm/cmpxchg.h
> index 58045c8983404..76f43db0890fc 100644
> --- a/arch/arc/include/asm/cmpxchg.h
> +++ b/arch/arc/include/asm/cmpxchg.h
> @@ -48,7 +48,7 @@
>  									\
>  	switch(sizeof((_p_))) {						\
>  	case 1:								\
> -		_prev_ = (__typeof__(*(ptr)))cmpxchg_emu_u8((volatile u8 *)_p_, (uintptr_t)_o_, (uintptr_t)_n_);	\
> +		_prev_ = (__typeof__(*(ptr)))cmpxchg_emu_u8((volatile u8 *__force)_p_, (uintptr_t)_o_, (uintptr_t)_n_);	\
>  		break;							\
>  	case 4:								\
>  		_prev_ = __cmpxchg(_p_, _o_, _n_);			\


Added to for-curr.

Thx,
-Vineet

Re: ARC: Use __force to suppress per-CPU cmpxchg complaints

Posted by Paul E. McKenney 1 month, 1 week ago

On Tue, Oct 15, 2024 at 10:33:14PM -0700, Vineet Gupta wrote:
> On 10/9/24 10:55, Paul E. McKenney wrote:
> > Currently, the cast of the first argument to cmpxchg_emu_u8() drops the
> > __percpu address-space designator, which results in sparse complaints
> > when applying cmpxchg() to per-CPU variables in ARC.  Therefore, use
> > __force to suppress these complaints, given that this does not pertain
> > to cmpxchg() semantics, which are plently well-defined on variables in
> > general, whether per-CPU or otherwise.
> >
> > Reported-by: kernel test robot <lkp@intel.com>
> > Closes: https://lore.kernel.org/oe-kbuild-all/202409251336.ToC0TvWB-lkp@intel.com/
> > Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
> > Cc: Vineet Gupta <vgupta@kernel.org>
> > Cc: <linux-snps-arc@lists.infradead.org>
> >
> > diff --git a/arch/arc/include/asm/cmpxchg.h b/arch/arc/include/asm/cmpxchg.h
> > index 58045c8983404..76f43db0890fc 100644
> > --- a/arch/arc/include/asm/cmpxchg.h
> > +++ b/arch/arc/include/asm/cmpxchg.h
> > @@ -48,7 +48,7 @@
> >  									\
> >  	switch(sizeof((_p_))) {						\
> >  	case 1:								\
> > -		_prev_ = (__typeof__(*(ptr)))cmpxchg_emu_u8((volatile u8 *)_p_, (uintptr_t)_o_, (uintptr_t)_n_);	\
> > +		_prev_ = (__typeof__(*(ptr)))cmpxchg_emu_u8((volatile u8 *__force)_p_, (uintptr_t)_o_, (uintptr_t)_n_);	\
> >  		break;							\
> >  	case 4:								\
> >  		_prev_ = __cmpxchg(_p_, _o_, _n_);			\
> 
> 
> Added to for-curr.

Thank you!  As soon as it shows up in -next, I will drop it from my tree.

							Thanx, Paul