The percpu-counter-sum code does a for_each_online_cpu() protected
by a spinlock, which makes it look like it needs to use
get/put_online_cpus_atomic(), going forward. However, the code has
adequate synchronization with CPU hotplug, via a hotplug callback
and the fbc->lock.
So use for_each_online_cpu_nocheck() to avoid false-positive warnings
from the hotplug locking validator. And add a comment justifying the
same.
Cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
Cc: Tejun Heo <tj@xxxxxxxxxx>
Signed-off-by: Srivatsa S. Bhat <srivatsa.bhat@xxxxxxxxxxxxxxxxxx>
---
lib/percpu_counter.c | 9 ++++++++-
1 file changed, 8 insertions(+), 1 deletion(-)
diff --git a/lib/percpu_counter.c b/lib/percpu_counter.c
index ba6085d..2d80e8a 100644
--- a/lib/percpu_counter.c
+++ b/lib/percpu_counter.c
@@ -98,9 +98,16 @@ s64 __percpu_counter_sum(struct percpu_counter *fbc)
s64 ret;
int cpu;
+ /*
+ * CPU hotplug synchronization is explicitly handled via the
+ * hotplug callback, which synchronizes through fbc->lock.
+ * So it is safe to use the _nocheck() version of
+ * for_each_online_cpu() here (to avoid false-positive warnings
+ * from the CPU hotplug debug code).
+ */
raw_spin_lock(&fbc->lock);
ret = fbc->count;
- for_each_online_cpu(cpu) {
+ for_each_online_cpu_nocheck(cpu) {
s32 *pcount = per_cpu_ptr(fbc->counters, cpu);
ret += *pcount;
}
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