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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

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 -
maintainer of: 2.6 Serial core
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