profile: Fix CPU hotplug callback registration
authorSrivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com>
Mon, 10 Mar 2014 20:42:08 +0000 (02:12 +0530)
committerRafael J. Wysocki <rafael.j.wysocki@intel.com>
Thu, 20 Mar 2014 12:43:48 +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 profile code by using this latter form of callback registration.

Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Mauro Carvalho Chehab <mchehab@redhat.com>
Cc: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
kernel/profile.c

index ebdd9c1a86b4dfd7840df57c64f13f72a1401156..93b2a3fe0a6475f1396fedc0cecd91ee69575cdc 100644 (file)
@@ -591,18 +591,28 @@ out_cleanup:
 int __ref create_proc_profile(void) /* false positive from hotcpu_notifier */
 {
        struct proc_dir_entry *entry;
+       int err = 0;
 
        if (!prof_on)
                return 0;
-       if (create_hash_tables())
-               return -ENOMEM;
+
+       cpu_notifier_register_begin();
+
+       if (create_hash_tables()) {
+               err = -ENOMEM;
+               goto out;
+       }
+
        entry = proc_create("profile", S_IWUSR | S_IRUGO,
                            NULL, &proc_profile_operations);
        if (!entry)
-               return 0;
+               goto out;
        proc_set_size(entry, (1 + prof_len) * sizeof(atomic_t));
-       hotcpu_notifier(profile_cpu_callback, 0);
-       return 0;
+       __hotcpu_notifier(profile_cpu_callback, 0);
+
+out:
+       cpu_notifier_register_done();
+       return err;
 }
 module_init(create_proc_profile);
 #endif /* CONFIG_PROC_FS */