linux-kernel - Re: [PATCH] [ARM] Unconditional call to smp_cross

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Message-ID: <20120524161733.GF6908@n2100.arm.linux.org.uk>
Date:	Thu, 24 May 2012 17:17:33 +0100
From:	Russell King - ARM Linux <linux@....linux.org.uk>
To:	Pantelis Antoniou <panto@...oniou-consulting.com>
Cc:	linux-kernel@...r.kernel.org, Russ.Dill@...com, mporter@...com,
	stable@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH] [ARM] Unconditional call to smp_cross_call on UP
	crashes

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.
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