net: Fix race condition in store_rps_map
There is a race condition in store_rps_map that allows jump label
count in rps_needed to go below zero. This can happen when
concurrently attempting to set and a clear map.
Scenario:
1. rps_needed count is zero
2. New map is assigned by setting thread, but rps_needed count _not_ yet
incremented (rps_needed count still zero)
2. Map is cleared by second thread, old_map set to that just assigned
3. Second thread performs static_key_slow_dec, rps_needed count now goes
negative
Fix is to increment or decrement rps_needed under the spinlock.
Signed-off-by: Tom Herbert <tom@herbertland.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/core/net-sysfs.c b/net/core/net-sysfs.c
index 194c1d0..39ec694 100644
--- a/net/core/net-sysfs.c
+++ b/net/core/net-sysfs.c
@@ -726,14 +726,17 @@
old_map = rcu_dereference_protected(queue->rps_map,
lockdep_is_held(&rps_map_lock));
rcu_assign_pointer(queue->rps_map, map);
- spin_unlock(&rps_map_lock);
if (map)
static_key_slow_inc(&rps_needed);
- if (old_map) {
- kfree_rcu(old_map, rcu);
+ if (old_map)
static_key_slow_dec(&rps_needed);
- }
+
+ spin_unlock(&rps_map_lock);
+
+ if (old_map)
+ kfree_rcu(old_map, rcu);
+
free_cpumask_var(mask);
return len;
}