linux-kernel - Re: [PATCH v2 04/23] xen/arm: sync

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Date:	Tue, 7 Aug 2012 14:13:29 -0400
From:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
To:	Stefano Stabellini <stefano.stabellini@...citrix.com>
Cc:	linux-kernel@...r.kernel.org, xen-devel@...ts.xensource.com,
	Ian.Campbell@...rix.com, tim@....org,
	linux-arm-kernel@...ts.infradead.org, linaro-dev@...ts.linaro.org,
	catalin.marinas@....com, arnd@...db.de
Subject: Re: [PATCH v2 04/23] xen/arm: sync_bitops

On Mon, Aug 06, 2012 at 03:27:07PM +0100, Stefano Stabellini wrote:
> sync_bitops functions are equivalent to the SMP implementation of the
> original functions, independently from CONFIG_SMP being defined.
> 
> We need them because _set_bit etc are not SMP safe if !CONFIG_SMP. But
> under Xen you might be communicating with a completely external entity
> who might be on another CPU (e.g. two uniprocessor guests communicating
> via event channels and grant tables). So we need a variant of the bit
> ops which are SMP safe even on a UP kernel.

Ack from me.
> 
> Signed-off-by: Stefano Stabellini <stefano.stabellini@...citrix.com>
> ---
>  arch/arm/include/asm/sync_bitops.h |   27 +++++++++++++++++++++++++++
>  1 files changed, 27 insertions(+), 0 deletions(-)
>  create mode 100644 arch/arm/include/asm/sync_bitops.h
> 
> diff --git a/arch/arm/include/asm/sync_bitops.h b/arch/arm/include/asm/sync_bitops.h
> new file mode 100644
> index 0000000..63479ee
> --- /dev/null
> +++ b/arch/arm/include/asm/sync_bitops.h
> @@ -0,0 +1,27 @@
> +#ifndef __ASM_SYNC_BITOPS_H__
> +#define __ASM_SYNC_BITOPS_H__
> +
> +#include <asm/bitops.h>
> +#include <asm/system.h>
> +
> +/* sync_bitops functions are equivalent to the SMP implementation of the
> + * original functions, independently from CONFIG_SMP being defined.
> + *
> + * We need them because _set_bit etc are not SMP safe if !CONFIG_SMP. But
> + * under Xen you might be communicating with a completely external entity
> + * who might be on another CPU (e.g. two uniprocessor guests communicating
> + * via event channels and grant tables). So we need a variant of the bit
> + * ops which are SMP safe even on a UP kernel.
> + */
> +
> +#define sync_set_bit(nr, p)		_set_bit(nr, p)
> +#define sync_clear_bit(nr, p)		_clear_bit(nr, p)
> +#define sync_change_bit(nr, p)		_change_bit(nr, p)
> +#define sync_test_and_set_bit(nr, p)	_test_and_set_bit(nr, p)
> +#define sync_test_and_clear_bit(nr, p)	_test_and_clear_bit(nr, p)
> +#define sync_test_and_change_bit(nr, p)	_test_and_change_bit(nr, p)
> +#define sync_test_bit(nr, addr)		test_bit(nr, addr)
> +#define sync_cmpxchg			cmpxchg
> +
> +
> +#endif
> -- 
> 1.7.2.5
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