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    SubjectRe: SMP BUG
    On Wed, Feb 15, 2006 at 03:23:02PM -0800, Linus Torvalds wrote:
    > Does this fix the ARM oops?

    It fixes that exact oops but only by preventing us getting that far
    due to another oops.

    We call cpu_up, which sends a CPU_UP_PREPARE event. This causes the
    migration thread to be spawned, and rq->migration_thread to be set.

    Eventually, we call the architecture __cpu_up(), which ends up
    calling init_idle(). Due to this patch, init_idle() then NULLs out
    rq->migration_thread.

    Later, we send a CPU_ONLINE event, which then tries to do
    wake_up_process(rq->migration_thread) - resulting in a NULL pointer
    deref in try_to_wake_up().

    Hence, with this patch, it looks like rq will be used prior to
    initialisation. I could try commenting out the migration_thread
    initialisation to NULL, but I suspect that there may be other
    problems associated with this patch (eg, rq->migration_queue).

    --
    Russell King
    Linux kernel 2.6 ARM Linux - http://www.arm.linux.org.uk/
    maintainer of: 2.6 Serial core
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