zsmalloc: Fix CPU 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 zsmalloc code by using this latter form of callback registration.

Cc: Nitin Gupta <ngupta@vflare.org>
Cc: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com>
Acked-by: Minchan Kim <minchan@kernel.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c
index c03ca5e9fe15c8b9725db0ac41b6ba78f64b0e5d..36b4591a7a2d3b2eca7111b26bee3efa19c7c5c5 100644 (file)
--- a/mm/zsmalloc.c
+++ b/mm/zsmalloc.c
@@ -814,21 +814,32 @@ static void zs_exit(void)
 {
        int cpu;
 
+       cpu_notifier_register_begin();
+
        for_each_online_cpu(cpu)
                zs_cpu_notifier(NULL, CPU_DEAD, (void *)(long)cpu);
-       unregister_cpu_notifier(&zs_cpu_nb);
+       __unregister_cpu_notifier(&zs_cpu_nb);
+
+       cpu_notifier_register_done();
 }
 
 static int zs_init(void)
 {
        int cpu, ret;
 
-       register_cpu_notifier(&zs_cpu_nb);
+       cpu_notifier_register_begin();
+
+       __register_cpu_notifier(&zs_cpu_nb);
        for_each_online_cpu(cpu) {
                ret = zs_cpu_notifier(NULL, CPU_UP_PREPARE, (void *)(long)cpu);
-               if (notifier_to_errno(ret))
+               if (notifier_to_errno(ret)) {
+                       cpu_notifier_register_done();
                        goto fail;
+               }
        }
+
+       cpu_notifier_register_done();
+
        return 0;
 fail:
        zs_exit();