x86, intel, uncore: Fix CPU hotplug callback registration
authorSrivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com>
Mon, 10 Mar 2014 20:36:57 +0000 (02:06 +0530)
committerRafael J. Wysocki <rafael.j.wysocki@intel.com>
Thu, 20 Mar 2014 12:43:42 +0000 (13:43 +0100)
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 uncore code in intel-x86 by using this latter form of callback
registration.

Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Arnaldo Carvalho de Melo <acme@ghostprotocols.net>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Signed-off-by: Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
arch/x86/kernel/cpu/perf_event_intel_uncore.c

index 047f540cf3f71cfe03f69d796a1957b8a58caebc..28922f62eb2990be0552802c3c3630ec2a354d8d 100644 (file)
@@ -3817,7 +3817,7 @@ static int __init uncore_cpu_init(void)
        if (ret)
                return ret;
 
-       get_online_cpus();
+       cpu_notifier_register_begin();
 
        for_each_online_cpu(cpu) {
                int i, phys_id = topology_physical_package_id(cpu);
@@ -3836,9 +3836,9 @@ static int __init uncore_cpu_init(void)
        }
        on_each_cpu(uncore_cpu_setup, NULL, 1);
 
-       register_cpu_notifier(&uncore_cpu_nb);
+       __register_cpu_notifier(&uncore_cpu_nb);
 
-       put_online_cpus();
+       cpu_notifier_register_done();
 
        return 0;
 }