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    SubjectRe: suspend race -next regression [Was: Power: fix suspend vt regression]
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    On Monday 31 August 2009, Jiri Slaby wrote:
    > On 08/11/2009 11:19 PM, Jiri Slaby wrote:
    > > However there is still a race or something. Sometimes the suspend goes
    > > through, sometimes it doesn't. I will investigate this further.
    >
    > Hmm, this took a loong time to track down a bit. Code instrumentation by
    > outb(XX, 0x80) usually caused the issue to disappear.
    >
    > However I found out that it's caused by might_sleep() calls in
    > flush_workqueue() and flush_cpu_workqueue(). I.e. it looks like there is
    > a task which deadlocks/spins forever. If we won't reschedule to it,
    > suspend proceeds.
    >
    > I replaced the latter might_sleep() by show_state() and removed
    > refrigerated tasks afterwards. The thing is that I don't know if the
    > prank task is there. I need a scheduler to store "next" task pid or
    > whatever to see what it picked as "next" and so what will run due to
    > might_sched(). I can then show it on port 80 display and read it when
    > the hangup occurs.
    >
    > Depending on which might_sleep(), either flush_workqueue() never (well,
    > at least in next 5 minutes) proceeds to for_each_cpu() or
    > wait_for_completion() in flush_cpu_workqueue() never returns.
    >
    > It's a regression against some -rc1 based -next tree. Bisection
    > impossible, suspend needs to be run even 7 times before it occurs. Maybe
    > a s/might_sleep/yield/ could make it happen earlier (going to try)?

    If /sys/class/rtc/rtc0/wakealarm works on this box, you can use it to trigger
    resume in a loop.

    Basically, you can do

    # echo 0 > /sys/class/rtc/rtc0/wakealarm
    # date +%s -d "+60 seconds" > /sys/class/rtc/rtc0/wakealarm

    then go to suspend and it will resume the box in ~1 minute.

    Thanks,
    Rafael


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