kstopmachine thread panic in do_exit (2.6.9-rc1-bk1)

[Nathan Lynch]

Hi-

Something crept in between 2.6.9-rc1 and 2.6.9-rc1-bk1 which reliably
trips the "Aiee, killing interrupt handler!" panic in do_exit when
offlining a cpu.  I inserted a BUG() before the panic call to see what's
causing it, looks like one of the kstopmachine threads spawned by
stop_machine.  I can't do a comparison with current -mm because
offlining a cpu doesn't even get that far there.

Backing out the most recent sched.c change ("sched: smt fixes" as of
this writing) fixes it.  Turning off preempt seems to work around it. 
The bug is still present in -bk2.  I'm seeing this on a 4-way ppc64
machine.

Nathan


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