Re: SMP BUG

[Russell King <rmk+lkml@arm.linux.org.uk>]

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