powerpc: NMI IPI make NMI IPIs fully sychronous
There is an asynchronous aspect to smp_send_nmi_ipi. The caller waits for all CPUs to call in to the handler, but it does not wait for completion of the handler. This is a needless complication, so remove it and always wait synchronously. The synchronous wait allows the caller to easily time out and clear the wait for completion (zero nmi_ipi_busy_count) in the case of badly behaved handlers. This would have prevented the recent smp_send_stop NMI IPI bug from causing the system to hang. Signed-off-by: NNicholas Piggin <npiggin@gmail.com> Signed-off-by: NMichael Ellerman <mpe@ellerman.id.au>
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