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>
(cherry picked from commit f0e71fcd0fa6f3f5495cd9ad3f1e4acd94446a55)
Signed-off-by: Alex Shi <alex.shi@linaro.org>

diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c
index 7a8d161b4cd76350b3e8c975a269d1f2596c1008..b728f10e353ba455f585ee47319bbdeb5a9a7f21 100644 (file)
--- a/mm/zsmalloc.c
+++ b/mm/zsmalloc.c
@@ -780,21 +780,32 @@ 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();