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    SubjectRe: [: [RFC] wake up notifications and suspend blocking (aka more wakelock stuff)]
    On Fri, Oct 14, 2011 at 07:01:16AM -0700, mark gross wrote:
    > On Thu, Oct 13, 2011 at 04:35:26PM +1100, NeilBrown wrote:
    > > On Wed, 12 Oct 2011 20:48:05 -0700 mark gross <markgross@thegnar.org> wrote:
    > >

    snip

    > > Can you describe a race?
    > > Here is the sequence as I see it.
    > >
    > > 0: some user-space process is blocking suspend by telling the suspend daemon
    > > not to suspend. There are no pending kernel wakeup events.
    > > All processes that handle wakeup events are registered with the daemon.
    > > 1: last blocking user-space process releases its "don't suspend" lock.
    > > 2: suspend-daemon decides to initiate suspend.
    > > 3: suspend_daemon reads wakeup_count and remembers number.
    > > 4: suspend daemon tells all registered clients that suspend is imminent.
    > > 5: each client executes 'poll' or 'select' or whatever and discovers that
    > > there are no events.
    > > 6: each client tells daemon that it is OK to suspend
    > > 7: when all votes are in, suspend daemon checks that no process is requesting
    > > that suspend be blocked.
    > > 8: if that succeeds, suspend daemon writes the number back to wakeup_count
    > > 9: if that succeeds, suspend daemon daemon writes 'mem' to 'state'.
    > > 10: goto 1
    > >
    > > If a wake_event happens after 3 and before 8, the write at 8 will fail.
    > > If a wake_event happens after 8, and before 9, the suspend will abort.
    > > If a wake_event happens after 9, the suspend will resume
    > > If a wake_event happens before 3, one of the processes will get an event
    > > notification from select or poll or whatever, and will ask the suspend
    > > daemon not to suspend just now and this will be noticed at 7, so 8 and 9
    > > will be skipped and we go straight to 10.
    > >
    > > No race.
    >
    > With the suspend daemon designed as above I see no race either. I was
    > thinking of a more trivial suspend daemon design and trying to fix it up
    > in the kernel.
    >

    After responding to this yesterday I still feel I'm missing something
    with respect to wake event acknowledgment. After a wake source becomes
    active how does it know its ok to become deactivate at the driver level?

    The race I'm now worried about is say a button press going up through
    the event layers. The event manager process, or X, (registered with the
    suspend daemon) is in a race to get the event and the socket based
    notification handshake described above.

    i.e. how is the key event delivery vrs unblocking of the suspend-daemon
    read of wakeup_count in step 3 race dealt with?

    Sorry for getting confused and flip flopping on you. This is pretty
    subtle stuff for me.

    --mark



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