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    SubjectRe: floppy.c soft lockup
    I hope Ingo will correct me if I am wrong,

    On 05/31, Mark Hounschell wrote:
    >
    > Oleg Nesterov wrote:
    > >
    > > So, the main question is: is it possible that one of RT processes/threads pins itself
    > > to some CPU and eats 100% cpu power?
    > >
    >
    > The main process is pinned to a processor(2) with all _non-kernel_ processes/threads forced over to processor 1.
    > Any already affinitized processes or kernel threads are left as is. Only user land stuff is moved. The main process
    > is for sure _not_ relinquishing it's processor(2) intentionally.

    This means that a non-rt kernel thread bound to CPU 2 can't run. In particular,
    events/2. This means that the problem is not directly connected to floppy.c,
    any flush_scheduled_work() (or schedule_on_each_cpu()) can't succeed.

    You can change irq/X/smp_affinity, but smp_apic_timer_interrupt() still can
    queue work_struct on CPU 2 (for example, mm/slab.c uses per-cpu reap_work).
    Since events/2 is blocked by the main RT thread, such a work_struct can't be
    executed, and so flush_scheduled_work() hangs.

    > All the I/O threads, floppy included, are running
    > on the other processor(1). During this failure only 1 or 2 of the I/O threads are actually doing anything.
    > I assume that what ever is going on in the kernel/floppy driver on behalf of the floppy thread is being done on processor 1?
    > Processor 1 has lots of CPU time available.

    Yes, but see above. flush_scheduled_work() needs a cooperation from events/2
    which is bound to CPU 2.

    If you changed irq/X/smp_affinity, the patch I sent should help, because
    floppy_work can't be scheduled on CPU 2, but still I don't think it is right
    to run 100% cpu-bound RT-process.

    Oleg.

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