Once stop_machine() is gone from the CPU offline path, we won't be able
to depend on disabling preemption to prevent CPUs from going offline
from under us.
Use the get/put_online_cpus_atomic() APIs to prevent CPUs from going
offline, while invoking from atomic context.
Cc: Al Viro <v...@zeniv.linux.org.uk>
Cc: Tejun Heo <t...@kernel.org>
Signed-off-by: Srivatsa S. Bhat <srivatsa.b...@linux.vnet.ibm.com>
---
lib/percpu_counter.c | 10 ++++++++++
1 file changed, 10 insertions(+)
diff --git a/lib/percpu_counter.c b/lib/percpu_counter.c
index ba6085d..f5e718d 100644
--- a/lib/percpu_counter.c
+++ b/lib/percpu_counter.c
@@ -98,6 +98,15 @@ s64 __percpu_counter_sum(struct percpu_counter *fbc)
s64 ret;
int cpu;
+ /*
+ * The calls to get/put_online_cpus_atomic() is strictly not
+ * necessary, since CPU hotplug is explicitly handled via the
+ * hotplug callback which synchronizes through fbc->lock.
+ * But we add them here anyway to make it easier for the debug
+ * code under CONFIG_DEBUG_HOTPLUG_CPU to validate the correctness
+ * of hotplug synchronization.
+ */
+ get_online_cpus_atomic();
raw_spin_lock(&fbc->lock);
ret = fbc->count;
for_each_online_cpu(cpu) {
@@ -105,6 +114,7 @@ s64 __percpu_counter_sum(struct percpu_counter *fbc)
ret += *pcount;
}
raw_spin_unlock(&fbc->lock);
+ put_online_cpus_atomic();
return ret;
}
EXPORT_SYMBOL(__percpu_counter_sum);
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