[PATCH] [ARM] Unconditional call to smp_cross_call on UP crashes

[Russell King - ARM Linux]

On Thu, May 24, 2012 at 07:50:24PM +0000, Pantelis Antoniou wrote:
> omap2plus_defconfig builds with SMP & SMP_ON_UP set.
> On beagle (which is UP) is_smp() returns false and we don't call
> smp_init_cpus which in turn does not initialize smp_cross_call which
> remains NULL.
> 
> When issuing a reboot we OOPS with a NULL dereference on stop smp_call.

I've been wondering whether we should make smp_cross_call() a no-op instead
by default, rather than a NULL pointer.

Alternatively, if may be well worth changing this to do:

	if (!cpumask_empty(&mask))
		smp_cross_call(&mask, IPI_CPU_STOP);

instead, so we avoid calling smp_cross_call() when we're on a SMP system
with only one CPU online.  I like this approach better because it removes
a potential call into platform code which is inappropriate.