Re: [PATCH v2 04/23] xen/arm: sync_bitops

Konrad Rzeszutek Wilk
2012-08-07T18:23:16Z

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@eu.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