linux-kernel - [PATCH 42/45] powerpc: Use get/put_online_cpus_atomic() to avoid false-positive warning

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Message-ID: <20130623134725.19094.9780.stgit@srivatsabhat.in.ibm.com>
Date:	Sun, 23 Jun 2013 19:17:29 +0530
From:	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>
To:	tglx@...utronix.de, peterz@...radead.org, tj@...nel.org,
	oleg@...hat.com, paulmck@...ux.vnet.ibm.com, rusty@...tcorp.com.au,
	mingo@...nel.org, akpm@...ux-foundation.org, namhyung@...nel.org,
	walken@...gle.com, vincent.guittot@...aro.org, laijs@...fujitsu.com
Cc:	rostedt@...dmis.org, wangyun@...ux.vnet.ibm.com,
	xiaoguangrong@...ux.vnet.ibm.com, sbw@....edu, fweisbec@...il.com,
	zhong@...ux.vnet.ibm.com, nikunj@...ux.vnet.ibm.com,
	srivatsa.bhat@...ux.vnet.ibm.com, linux-pm@...r.kernel.org,
	linux-arch@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Paul Mackerras <paulus@...ba.org>,
	Kumar Gala <galak@...nel.crashing.org>,
	Zhao Chenhui <chenhui.zhao@...escale.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	linuxppc-dev@...ts.ozlabs.org
Subject: [PATCH 42/45] powerpc: Use get/put_online_cpus_atomic() to avoid
 false-positive warning

Bringing a secondary CPU online is a special case in which, accessing
the cpu_online_mask is safe, even though that task (which running on the
CPU coming online) is not the hotplug writer.

It is a little hard to teach this to the debugging checks under
CONFIG_DEBUG_HOTPLUG_CPU. But luckily powerpc is one of the few places
where the CPU coming online traverses the cpu_online_mask before fully
coming online. So wrap that part under get/put_online_cpus_atomic(), to
avoid false-positive warnings from the CPU hotplug debug code.

Cc: Benjamin Herrenschmidt <benh@...nel.crashing.org>
Cc: Paul Mackerras <paulus@...ba.org>
Cc: Kumar Gala <galak@...nel.crashing.org>
Cc: Zhao Chenhui <chenhui.zhao@...escale.com>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: linuxppc-dev@...ts.ozlabs.org
Signed-off-by: Srivatsa S. Bhat <srivatsa.bhat@...ux.vnet.ibm.com>
---

 arch/powerpc/kernel/smp.c |    2 ++
 1 file changed, 2 insertions(+)

diff --git a/arch/powerpc/kernel/smp.c b/arch/powerpc/kernel/smp.c
index 2123bec..59c9a09 100644
--- a/arch/powerpc/kernel/smp.c
+++ b/arch/powerpc/kernel/smp.c
@@ -657,6 +657,7 @@ __cpuinit void start_secondary(void *unused)
 		cpumask_set_cpu(base + i, cpu_core_mask(cpu));
 	}
 	l2_cache = cpu_to_l2cache(cpu);
+	get_online_cpus_atomic();
 	for_each_online_cpu(i) {
 		struct device_node *np = cpu_to_l2cache(i);
 		if (!np)
@@ -667,6 +668,7 @@ __cpuinit void start_secondary(void *unused)
 		}
 		of_node_put(np);
 	}
+	put_online_cpus_atomic();
 	of_node_put(l2_cache);
 
 	local_irq_enable();

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