linux-kernel - Re: [RFC] Add implicit barriers to irqsave/restore class of functions

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Date:	Wed, 3 Apr 2013 18:59:36 +0530
From:	Vineet Gupta <Vineet.Gupta1@...opsys.com>
To:	Christian Ruppert <christian.ruppert@...lis.com>
CC:	Thomas Gleixner <tglx@...utronix.de>,
	Pierrick Hascoet <pierrick.hascoet@...lis.com>,
	LKML <linux-kernel@...r.kernel.org>,
	"Peter Zijlstra" <peterz@...radead.org>,
	Ingo Molnar <mingo@...nel.org>
Subject: Re: [RFC] Add implicit barriers to irqsave/restore class of functions

Hi Christian,

On 04/03/2013 06:40 PM, Christian Ruppert wrote:
> This patch adds implicit memory barriers to irqsave/restore functions of
> the ARC architecture port in line with what is done in other architectures.
>
> It seems to fix several seemingly unrelated issues in our platform but for
> the moment it is insufficiently tested (and might even be incomplete).
> Please comment.

I think this is not needed. Semantically we need barrier for spinlocks, not irq
save/restore - although spin locks are one of the primary users of irq
save/restore API.

So repeating what Thomas already said, the barrier already exists for
PREEMPT_COUNT, we need to make sure they are present for !PREEMPT_COUNT.

-Vineet

> Signed-off-by: Christian Ruppert <christian.ruppert@...lis.com>
> ---
>  arch/arc/include/asm/irqflags.h |    8 ++++----
>  1 files changed, 4 insertions(+), 4 deletions(-)
>
> diff --git a/arch/arc/include/asm/irqflags.h b/arch/arc/include/asm/irqflags.h
> index ccd8480..c8147d1 100644
> --- a/arch/arc/include/asm/irqflags.h
> +++ b/arch/arc/include/asm/irqflags.h
> @@ -39,7 +39,7 @@ static inline long arch_local_irq_save(void)
>  	"	flag.nz %0		\n"
>  	: "=r"(temp), "=r"(flags)
>  	: "n"((STATUS_E1_MASK | STATUS_E2_MASK))
> -	: "cc");
> +	: "memory", "cc");
>  
>  	return flags;
>  }
> @@ -53,7 +53,7 @@ static inline void arch_local_irq_restore(unsigned long flags)
>  	__asm__ __volatile__(
>  	"	flag %0			\n"
>  	:
> -	: "r"(flags));
> +	: "r"(flags) : "memory");
>  }
>  
>  /*
> @@ -73,7 +73,7 @@ static inline void arch_local_irq_disable(void)
>  	"	and %0, %0, %1		\n"
>  	"	flag %0			\n"
>  	: "=&r"(temp)
> -	: "n"(~(STATUS_E1_MASK | STATUS_E2_MASK)));
> +	: "n"(~(STATUS_E1_MASK | STATUS_E2_MASK)) : "memory");
>  }
>  
>  /*
> @@ -85,7 +85,7 @@ static inline long arch_local_save_flags(void)
>  
>  	__asm__ __volatile__(
>  	"	lr  %0, [status32]	\n"
> -	: "=&r"(temp));
> +	: "=&r"(temp) : : "memory");
>  
>  	return temp;
>  }

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