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    SubjectRe: [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@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


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