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    SubjectRe: [PATCHv4 04/11] PM: Use *_dec_not_zero instead of *_add_unless
    Date
    On Wednesday, July 27, 2011, Pavel Machek wrote:
    > Hi!
    >
    > > > atomic_dec_not_zero is defined for each architecture through
    > > > <linux/atomic.h> to provide the functionality of
    > > > atomic_add_unless(x, -1, 0).
    > > >
    > > > Signed-off-by: Sven Eckelmann <sven@narfation.org>
    > > > Cc: Len Brown <len.brown@intel.com>
    > > > Cc: Pavel Machek <pavel@ucw.cz>
    > > > Cc: Rafael J. Wysocki <rjw@sisk.pl>
    > > > Cc: linux-pm@lists.linux-foundation.org
    > >
    > > Acked-by: Rafael J. Wysocki <rjw@sisk.pl>
    > >
    > > > ---
    > > > drivers/base/power/runtime.c | 4 ++--
    > > > include/linux/pm_runtime.h | 2 +-
    > > > kernel/power/hibernate.c | 4 ++--
    > > > kernel/power/user.c | 2 +-
    > > > 4 files changed, 6 insertions(+), 6 deletions(-)
    > > >
    > > > diff --git a/drivers/base/power/runtime.c b/drivers/base/power/runtime.c
    > > > index 8dc247c..bda10d9 100644
    > > > --- a/drivers/base/power/runtime.c
    > > > +++ b/drivers/base/power/runtime.c
    > > > @@ -401,7 +401,7 @@ static int rpm_suspend(struct device *dev, int rpmflags)
    > > >
    > > > if (dev->parent) {
    > > > parent = dev->parent;
    > > > - atomic_add_unless(&parent->power.child_count, -1, 0);
    > > > + atomic_dec_not_zero(&parent->power.child_count);
    >
    > I'd like to understand... Why not atomic_dec in the first place? Count
    > should be exact, anyway, or we run into problems, right?

    Well, we'll also run into trouble if the count becomes negative. We might
    throw a WARN_ON() there if the old value weren't as expected, but that
    would be a separate patch.

    Thanks,
    Rafael


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