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_maps_update_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_maps_update_done();
Fix the vmstat code in the MM subsystem by using this latter form of callback
registration.
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Christoph Lameter <cl@xxxxxxxxx>
Cc: Rik van Riel <riel@xxxxxxxxxx>
Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
Cc: Yasuaki Ishimatsu <isimatu.yasuaki@xxxxxxxxxxxxxx>
Cc: Cody P Schafer <cody@xxxxxxxxxxxxxxxxxx>
Cc: Toshi Kani <toshi.kani@xxxxxx>
Cc: Dave Hansen <dave@xxxxxxxx>
Cc: linux-mm@xxxxxxxxx
Signed-off-by: Srivatsa S. Bhat <srivatsa.bhat@xxxxxxxxxxxxxxxxxx>
---
mm/vmstat.c | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)
diff --git a/mm/vmstat.c b/mm/vmstat.c
index 7249614..70668ba 100644
--- a/mm/vmstat.c
+++ b/mm/vmstat.c
@@ -1290,14 +1290,14 @@ static int __init setup_vmstat(void)
#ifdef CONFIG_SMP
int cpu;
- register_cpu_notifier(&vmstat_notifier);
+ cpu_maps_update_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_maps_update_done();
#endif
#ifdef CONFIG_PROC_FS
proc_create("buddyinfo", S_IRUGO, NULL, &fragmentation_file_operations);
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