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    SubjectRe: 2.6.14-rc1-git-now still dying in mm/slab - this time line 1849
    On Mon, 19 Sep 2005, Andrew Morton wrote:

    > Well. The CPU_UP_CANCELED locking in cpuup_callback() looks borked to me -
    > it takes cachep->nodelists[node]->list_lock and then calls
    > drain_alien_cache() which appears to take the same lock. But that's not
    > the problem here.
    >
    > The code in cache_reap() recalculates numa_node_id() multiple times, so if
    > the caller changes CPUs then this assertion will trigger. However it's
    > running under keventd here, which is pinned to a single CPU. Still, it
    > would be useful if you could try putting preempt_disable()s in
    > cache_reap(), or change cache_reap() to evaluate numa_node_id() just the
    > once, and cache that in a local variable.

    drain_array_cache_locked calls check_spinlock_acquired_node which is in
    turn insuring that interrupts are off. So no move to a different processor
    should be possible.

    However, that is contradicted by __wake_up calling
    drain_array_cache_locked. The process just woke up?

    > I wonder why numa_node_id() uses raw_smp_processor_id()? That's just
    > asking for preempt non-atomicity bugs.

    Accessing arrays indexed by node number even works if the process
    continues to be executed on another node.

    -
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