| From | "Srivatsa S. Bhat" <> | Subject | [PATCH 49/51] mm, zswap: Fix CPU hotplug callback registration | Date | Thu, 06 Feb 2014 03:43:37 +0530 |
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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@kvack.org Signed-off-by: Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com> ---
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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