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    SubjectRe: [RFC][PATCH] PM: Avoid losing wakeup events during suspend
    On Mon, 21 Jun 2010 12:54:44 -0400 (EDT)
    Alan Stern <stern@rowland.harvard.edu> wrote:

    > On Mon, 21 Jun 2010, Florian Mickler wrote:
    >
    > > > > > What happens if an event arrives just before you read
    > > > > > /sys/power/wakeup_count, but the userspace consumer doesn't realize
    > > > > > there is a new unprocessed event until after the power manager checks
    > > > > > it?
    > > >
    > > > > I think this is not the kernel's problem. In this approach the kernel makes it
    > > > > possible for the user space to avoid the race. Whether or not the user space
    > > > > will use this opportunity is a different matter.
    > > >
    > > > It is _not_ possible for userspace to avoid this race. Help from the
    > > > kernel is needed.
    > >
    > > It is possible if every (relevant) userspace program implements a
    > > callback for the powermanager to check if one of it's wakeup-sources
    > > got activated.
    > >
    > > That way the powermanager would read /sys/power/wakeup_count, then do
    > > the roundtrip to all it's registered users and only then suspend.
    >
    > After further thought, there's still a race:

    Ah, yes. That's what I meant in my other mail with 'how to determine
    that an wake event is in flight'.

    Read this too late.

    > Alan Stern

    Cheers,
    Flo


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