[v3,49/52] mm, vmstat: Fix CPU hotplug callback registration

Commit Message

Srivatsa S. Bhat March 10, 2014, 8:42 p.m. UTC

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 vmstat code in the MM subsystem by using this latter form of callback
registration.

Cc: Andrew Morton <[e-mail]>
Cc: Johannes Weiner <[e-mail]>
Cc: Cody P Schafer <[e-mail]>
Cc: Toshi Kani <[e-mail]>
Cc: Dave Hansen <[e-mail]>
Cc: Ingo Molnar <[e-mail]>
Cc: [e-mail]
Acked-by: Christoph Lameter <[e-mail]>
Acked-by: Rik van Riel <[e-mail]>
Reviewed-by: Yasuaki Ishimatsu <[e-mail]>
Signed-off-by: Srivatsa S. Bhat <[e-mail]>
---

 mm/vmstat.c |    6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)


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Patch

diff --git a/mm/vmstat.c b/mm/vmstat.c
index def5dd2..58c6f3d 100644
--- a/mm/vmstat.c
+++ b/mm/vmstat.c
@@ -1292,14 +1292,14 @@  static int __init setup_vmstat(void)
 #ifdef CONFIG_SMP
 	int cpu;
 
-	register_cpu_notifier(&vmstat_notifier);
+	cpu_notifier_register_begin();
+	__register_cpu_notifier(&vmstat_notifier);
 
-	get_online_cpus();
 	for_each_online_cpu(cpu) {
 		start_cpu_timer(cpu);
 		node_set_state(cpu_to_node(cpu), N_CPU);
 	}
-	put_online_cpus();
+	cpu_notifier_register_done();
 #endif
 #ifdef CONFIG_PROC_FS
 	proc_create("buddyinfo", S_IRUGO, NULL, &fragmentation_file_operations);