xfrm: avoid spinlock in get_acqseq()

Use atomic_inc_return() in get_acqseq() to avoid taking a spinlock

Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/key/af_key.c b/net/key/af_key.c
index 4744b1f..e2aacf0 100644
--- a/net/key/af_key.c
+++ b/net/key/af_key.c
@@ -3019,12 +3019,11 @@
 static u32 get_acqseq(void)
 {
 	u32 res;
-	static u32 acqseq;
-	static DEFINE_SPINLOCK(acqseq_lock);
+	static atomic_t acqseq;
 
-	spin_lock_bh(&acqseq_lock);
-	res = (++acqseq ? : ++acqseq);
-	spin_unlock_bh(&acqseq_lock);
+	do {
+		res = atomic_inc_return(&acqseq);
+	} while (!res);
 	return res;
 }