Date: Fri, 18 Dec 2015 15:07:53 -0800
From: Andrew Morton <akpm@linux-foundation.org>
To: Sudip Mukherjee <sudipm.mukherjee@gmail.com>
Cc: linux-kernel@vger.kernel.org, Chris Wilson <chris@chris-wilson.co.uk>,
        Ingo Molnar <mingo@kernel.org>,
        Stephen Rothwell <sfr@canb.auug.org.au>
Subject: Re: [PATCH] Revert
 "kernel/stop_machine.c: remove CONFIG_SMP dependencies"
Message-Id: <20151218150753.6fa343f146682f17800c3b0a@linux-foundation.org>
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References: <1450433155-31615-1-git-send-email-sudipm.mukherjee@gmail.com>
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On Fri, 18 Dec 2015 15:35:55 +0530 Sudip Mukherjee <sudipm.mukherjee@gmail.com> wrote:

> This reverts commit 64dab25b058c12f935794cb239089303bda7dbc1.
> 
> CONFIG_SMP dependency is needed for some arch like tile, tilegx and
> m32r. They use stop_machine() but they donot have HOTPLUG_CPU and as a
> result their builds are failing with "undefined symbol 'stop_machine'".

Thanks.  I had my &&'s and ||'s mixed up.   I did this:

--- a/kernel/stop_machine.c~kernel-stop_machinec-remove-config_smp-dependencies-fix
+++ a/kernel/stop_machine.c
@@ -531,8 +531,6 @@ static int __init cpu_stop_init(void)
 }
 early_initcall(cpu_stop_init);
 
-#ifdef CONFIG_HOTPLUG_CPU
-
 static int __stop_machine(cpu_stop_fn_t fn, void *data, const struct cpumask *cpus)
 {
 	struct multi_stop_data msdata = {
@@ -630,5 +628,3 @@ int stop_machine_from_inactive_cpu(cpu_s
 	mutex_unlock(&stop_cpus_mutex);
 	return ret ?: done.ret;
 }
-
-#endif	/* CONFIG_HOTPLUG_CPU */
_


Rationale:

stop_machine.o is only built when CONFIG_SMP=y so

#if defined(CONFIG_SMP) || defined(CONFIG_HOTPLUG_CPU)

always evaluates to true, so remove it.


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