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

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Message-ID: <c1afa8ac-5c6a-4966-975d-915887c8106d@kernel.org>
Date: Tue, 15 Oct 2024 22:33:14 -0700
From: Vineet Gupta <vgupta@...nel.org>
To: paulmck@...nel.org, linux-arch@...r.kernel.org,
 linux-kernel@...r.kernel.org, linux-snps-arc@...ts.infradead.org
Cc: vgupta@...nel.org
Subject: Re: ARC: Use __force to suppress per-CPU cmpxchg complaints

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