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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>
This commit is contained in:
Tom Herbert 2015-08-05 09:39:27 -07:00 committed by David S. Miller
parent e05176a328
commit 10e4ea7514
1 changed files with 7 additions and 4 deletions
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11
net/core/net-sysfs.c
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@ -726,14 +726,17 @@ static ssize_t store_rps_map(struct netdev_rx_queue *queue,
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;
}