cxgb4: smt: Add lock for atomic_dec_and_test

The atomic_dec_and_test() is not safe because it is
outside of locks.
Move the locks of t4_smte_free() to its caller,
cxgb4_smt_release() to protect the atomic decrement.

Fixes: 3bdb376 ("cxgb4: introduce SMT ops to prepare for SMAC rewrite support")
Signed-off-by: Chuhong Yuan <hslester96@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/chelsio/cxgb4/smt.c

@@ -97,11 +97,9 @@ static struct smt_entry *find_or_alloc_smte(struct smt_data *s, u8 *smac)
 
 static void t4_smte_free(struct smt_entry *e)
 {
-	spin_lock_bh(&e->lock);
 	if (atomic_read(&e->refcnt) == 0) {  /* hasn't been recycled */
 		e->state = SMT_STATE_UNUSED;
 	}
-	spin_unlock_bh(&e->lock);
 }
 
 /**
@@ -111,8 +109,10 @@ static void t4_smte_free(struct smt_entry *e)
  */
 void cxgb4_smt_release(struct smt_entry *e)
 {
+	spin_lock_bh(&e->lock);
 	if (atomic_dec_and_test(&e->refcnt))
 		t4_smte_free(e);
+	spin_unlock_bh(&e->lock);
 }
 EXPORT_SYMBOL(cxgb4_smt_release);