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    SubjectRe: 2.6-bk: cpu hotplug + preempt = smp_processor_id warnings galore
    On Sat, Feb 12, 2005 at 11:59:04AM -0700, Zwane Mwaikambo wrote:
    > How about;
    >
    > Index: linux-2.6.11-rc3-mm2/kernel/softirq.c
    > ===================================================================
    > RCS file: /home/cvsroot/linux-2.6.11-rc3-mm2/kernel/softirq.c,v
    > retrieving revision 1.1.1.1
    > diff -u -p -B -r1.1.1.1 softirq.c
    > --- linux-2.6.11-rc3-mm2/kernel/softirq.c 11 Feb 2005 05:14:57 -0000 1.1.1.1
    > +++ linux-2.6.11-rc3-mm2/kernel/softirq.c 12 Feb 2005 18:24:54 -0000
    > @@ -355,8 +355,12 @@ static int ksoftirqd(void * __bind_cpu)
    > set_current_state(TASK_INTERRUPTIBLE);
    >
    > while (!kthread_should_stop()) {
    > - if (!local_softirq_pending())
    > + preempt_disable();
    > + if (!local_softirq_pending()) {
    > + preempt_enable_no_resched();
    > schedule();
    > + preempt_disable();
    > + }
    >
    > __set_current_state(TASK_RUNNING);
    >
    > @@ -364,14 +368,14 @@ static int ksoftirqd(void * __bind_cpu)
    > /* Preempt disable stops cpu going offline.
    > If already offline, we'll be on wrong CPU:
    > don't process */
    > - preempt_disable();
    > if (cpu_is_offline((long)__bind_cpu))
    > goto wait_to_die;
    > do_softirq();
    > - preempt_enable();
    > + preempt_enable_no_resched();
    > cond_resched();
    > + preempt_disable();
    > }
    > -
    > + preempt_enable();
    > set_current_state(TASK_INTERRUPTIBLE);
    > }
    > __set_current_state(TASK_RUNNING);
    >

    Works ok here.

    It looks as if we need to explicitly bind worker threads to a newly
    onlined cpu. This gets rid of the smp_processor_id warnings from
    cache_reap. Adding a little more instrumentation to the debug
    smp_processor_id showed that new worker threads were actually running
    on the wrong cpu...

    Does this look ok?

    Index: linux-2.6.11-rc4-bk2/kernel/workqueue.c
    ===================================================================
    --- linux-2.6.11-rc4-bk2.orig/kernel/workqueue.c 2005-02-14 11:13:08.000000000 -0600
    +++ linux-2.6.11-rc4-bk2/kernel/workqueue.c 2005-02-14 15:18:35.000000000 -0600
    @@ -485,8 +485,10 @@

    case CPU_ONLINE:
    /* Kick off worker threads. */
    - list_for_each_entry(wq, &workqueues, list)
    + list_for_each_entry(wq, &workqueues, list) {
    + kthread_bind(wq->cpu_wq[hotcpu].thread, hotcpu);
    wake_up_process(wq->cpu_wq[hotcpu].thread);
    + }
    break;

    case CPU_UP_CANCELED:
    -
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