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 sysfs code in sparc by using this latter form of callback
registration.
Cc: "David S. Miller" <da...@davemloft.net>
Cc: sparcli...@vger.kernel.org
Signed-off-by: Srivatsa S. Bhat <srivatsa.b...@linux.vnet.ibm.com>
---
arch/sparc/kernel/sysfs.c | 6 +++++-
1 file changed, 5 insertions(+), 1 deletion(-)
diff --git a/arch/sparc/kernel/sysfs.c b/arch/sparc/kernel/sysfs.c
index c21c673..2177b9e 100644
--- a/arch/sparc/kernel/sysfs.c
+++ b/arch/sparc/kernel/sysfs.c
@@ -300,7 +300,7 @@ static int __init topology_init(void)
check_mmu_stats();
- register_cpu_notifier(&sysfs_cpu_nb);
+ cpu_maps_update_begin();
for_each_possible_cpu(cpu) {
struct cpu *c = &per_cpu(cpu_devices, cpu);
@@ -310,6 +310,10 @@ static int __init topology_init(void)
register_cpu_online(cpu);
}
+ __register_cpu_notifier(&sysfs_cpu_nb);
+
+ cpu_maps_update_done();
+
return 0;
}
--
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