Re: qemu:arm test failure due to commit 8053871d0f7f (smp: Fix smp_call_function_single_async() locking)

[Rabin Vincent]

On Sun, Apr 19, 2015 at 08:01:40PM +0200, Ingo Molnar wrote:
> That's all fine and good, but why is an IPI sent to a non-existent 
> CPU? It's not like we don't know which CPU is up and down.

The perf events code is trying to call smp_call_function_single() on the
non-existent CPU in perf_event_exit_cpu_context() while handling the
CPU_UP_CANCELED notification.  perf_cpu_notify() handles CPU_UP_CANCELED
and CPU_DOWN_PREPARE in the same way.

(cpu_up() is tried for the non-existing CPUs because in this case what
 is specified in the device tree does not match reality.)
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