[PATCH v2 23/52] x86, intel, cacheinfo: Fix CPU hotplug callback registration

From: Srivatsa S. Bhat
Date: Fri Feb 14 2014 - 03:00:20 EST


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 intel cacheinfo code in x86 by using this latter form of callback
registration.

Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: "H. Peter Anvin" <hpa@xxxxxxxxx>
Cc: x86@xxxxxxxxxx
Cc: Borislav Petkov <bp@xxxxxxx>
Signed-off-by: Srivatsa S. Bhat <srivatsa.bhat@xxxxxxxxxxxxxxxxxx>
---

arch/x86/kernel/cpu/intel_cacheinfo.c | 13 ++++++++-----
1 file changed, 8 insertions(+), 5 deletions(-)

diff --git a/arch/x86/kernel/cpu/intel_cacheinfo.c b/arch/x86/kernel/cpu/intel_cacheinfo.c
index 0641113..a952e9c 100644
--- a/arch/x86/kernel/cpu/intel_cacheinfo.c
+++ b/arch/x86/kernel/cpu/intel_cacheinfo.c
@@ -1225,21 +1225,24 @@ static struct notifier_block cacheinfo_cpu_notifier = {

static int __init cache_sysfs_init(void)
{
- int i;
+ int i, err = 0;

if (num_cache_leaves == 0)
return 0;

+ cpu_notifier_register_begin();
for_each_online_cpu(i) {
- int err;
struct device *dev = get_cpu_device(i);

err = cache_add_dev(dev);
if (err)
- return err;
+ goto out;
}
- register_hotcpu_notifier(&cacheinfo_cpu_notifier);
- return 0;
+ __register_hotcpu_notifier(&cacheinfo_cpu_notifier);
+
+out:
+ cpu_notifier_register_done();
+ return err;
}

device_initcall(cache_sysfs_init);

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