linux-kernel - [PATCH v2 05/52] ia64, salinfo: Fix hotplug callback registration

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Message-ID: <20140214075019.22701.79255.stgit@srivatsabhat.in.ibm.com>
Date:	Fri, 14 Feb 2014 13:20:20 +0530
From:	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>
To:	paulus@...ba.org, oleg@...hat.com, mingo@...nel.org,
	rusty@...tcorp.com.au, peterz@...radead.org, tglx@...utronix.de,
	akpm@...ux-foundation.org
Cc:	paulmck@...ux.vnet.ibm.com, tj@...nel.org, walken@...gle.com,
	ego@...ux.vnet.ibm.com, linux@....linux.org.uk, rjw@...ysocki.net,
	linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org,
	srivatsa.bhat@...ux.vnet.ibm.com, Tony Luck <tony.luck@...el.com>,
	Fenghua Yu <fenghua.yu@...el.com>,
	Ingo Molnar <mingo@...nel.org>, linux-ia64@...r.kernel.org,
	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>
Subject: [PATCH v2 05/52] ia64, salinfo: Fix hotplug callback registration

Subsystems that want to register CPU hotplug callbacks, as well as perform
initialization for the CPUs that are already online, often do it as shown
below:

	get_online_cpus();

	for_each_online_cpu(cpu)
		init_cpu(cpu);

	register_cpu_notifier(&foobar_cpu_notifier);

	put_online_cpus();

This is wrong, since it is prone to ABBA deadlocks involving the
cpu_add_remove_lock and the cpu_hotplug.lock (when running concurrently
with CPU hotplug operations).

Instead, the correct and race-free way of performing the callback
registration is:

	cpu_notifier_register_begin();

	for_each_online_cpu(cpu)
		init_cpu(cpu);

	/* Note the use of the double underscored version of the API */
	__register_cpu_notifier(&foobar_cpu_notifier);

	cpu_notifier_register_done();


Fix the salinfo code in ia64 by using this latter form of callback
registration.

Cc: Tony Luck <tony.luck@...el.com>
Cc: Fenghua Yu <fenghua.yu@...el.com>
Cc: Ingo Molnar <mingo@...nel.org>
Cc: linux-ia64@...r.kernel.org
Signed-off-by: Srivatsa S. Bhat <srivatsa.bhat@...ux.vnet.ibm.com>
---

 arch/ia64/kernel/salinfo.c |    6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/arch/ia64/kernel/salinfo.c b/arch/ia64/kernel/salinfo.c
index 960a396..ee9719e 100644
--- a/arch/ia64/kernel/salinfo.c
+++ b/arch/ia64/kernel/salinfo.c
@@ -635,6 +635,8 @@ salinfo_init(void)
 					   (void *)salinfo_entries[i].feature);
 	}
 
+	cpu_notifier_register_begin();
+
 	for (i = 0; i < ARRAY_SIZE(salinfo_log_name); i++) {
 		data = salinfo_data + i;
 		data->type = i;
@@ -669,7 +671,9 @@ salinfo_init(void)
 	salinfo_timer.function = &salinfo_timeout;
 	add_timer(&salinfo_timer);
 
-	register_hotcpu_notifier(&salinfo_cpu_notifier);
+	__register_hotcpu_notifier(&salinfo_cpu_notifier);
+
+	cpu_notifier_register_done();
 
 	return 0;
 }

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