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 zswap code by using this latter form of callback registration.
Cc: linux-mm@xxxxxxxxx
Signed-off-by: Srivatsa S. Bhat <srivatsa.bhat@xxxxxxxxxxxxxxxxxx>
---
mm/zswap.c | 8 ++++----
1 file changed, 4 insertions(+), 4 deletions(-)
diff --git a/mm/zswap.c b/mm/zswap.c
index e55bab9..681fa3f 100644
--- a/mm/zswap.c
+++ b/mm/zswap.c
@@ -387,18 +387,18 @@ static int zswap_cpu_init(void)
{
unsigned long cpu;
- get_online_cpus();
+ cpu_maps_update_begin();
for_each_online_cpu(cpu)
if (__zswap_cpu_notifier(CPU_UP_PREPARE, cpu) != NOTIFY_OK)
goto cleanup;
- register_cpu_notifier(&zswap_cpu_notifier_block);
- put_online_cpus();
+ __register_cpu_notifier(&zswap_cpu_notifier_block);
+ cpu_maps_update_done();
return 0;
cleanup:
for_each_online_cpu(cpu)
__zswap_cpu_notifier(CPU_UP_CANCELED, cpu);
- put_online_cpus();
+ cpu_maps_update_done();
return -ENOMEM;
}
--
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