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    SubjectRe: 2.6.22-rc1: Broken suspend on SMP with tifm
    Date
    On Sunday, 13 May 2007 22:30, Oleg Nesterov wrote:
    > On 05/14, Oleg Nesterov wrote:
    > >
    > > On 05/13, Rafael J. Wysocki wrote:
    > > >
    > > > The suspend/hibernation is broken on SMP due to:
    > > >
    > > > commit 3540af8ffddcdbc7573451ac0b5cd57a2eaf8af5
    > > > tifm: replace per-adapter kthread with freezeable workqueue
    > > >
    > > > Well, it looks like freezable worqueues still deadlock with CPU hotplug
    > > > when worker threads are frozen.
    > >
    > > Ugh. I thought we deprecated create_freezeable_workqueue(), exactly
    > > because suspend was changed to call _cpu_down() after freeze().
    > >
    > > It is not that "looks like freezable worqueues still deadlock", it
    > > is "of course, freezable worqueues deadlocks" on CPU_DEAD.
    > >
    > > The ->freezeable is still here just because of incoming "cpu-hotplug
    > > using freezer" rework.
    > >
    > > No?
    > >
    > > > --- linux-2.6.22-rc1.orig/kernel/workqueue.c
    > > > +++ linux-2.6.22-rc1/kernel/workqueue.c
    > > > @@ -799,9 +799,7 @@ static int __devinit workqueue_cpu_callb
    > > > struct cpu_workqueue_struct *cwq;
    > > > struct workqueue_struct *wq;
    > > >
    > > > - action &= ~CPU_TASKS_FROZEN;
    > > > -
    > > > - switch (action) {
    > > > + switch (action & ~CPU_TASKS_FROZEN) {
    > >
    > > Confused. How can we see, say CPU_UP_PREPARE_FROZEN, if we cleared
    > > CPU_TASKS_FROZEN bit?
    >
    > So, unless I missed something stupid, this patch is not 100% right.

    Well, it isn't, but for a different reason (see [*] below).

    > I think the better fix (at least for now) is
    >
    > - #define create_freezeable_workqueue(name) __create_workqueue((name), 0, 1)
    > + #define create_freezeable_workqueue(name) __create_workqueue((name), 1, 1)
    >
    > Alex, do you really need a multithreaded wq?
    >
    > Rafael, what do you think?

    That would be misleading if the driver needs the threads to be frozen.

    I would prefer to revert the commit that caused the problem to appear, but it
    doesn't revert cleanly and I hate to invalidate someone else's work becuase of
    my own mistakes.

    [*] Getting back to the patch, it seems to me that we should do something like
    take_over_work() before thawing the frozen thread, because there may be a queue
    to process and the device is suspended at that point.

    Greetings,
    Rafael
    -
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