xfrm: Use GFP_ATOMIC in xfrm_compile_policy

As xfrm_compile_policy runs within a read_lock, we cannot use
GFP_KERNEL for memory allocations.

Reported-by: Luca Tettamanti <kronos.it@gmail.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/xfrm/xfrm_user.c b/net/xfrm/xfrm_user.c
index ba59983..b14ed4b 100644
--- a/net/xfrm/xfrm_user.c
+++ b/net/xfrm/xfrm_user.c
@@ -2504,7 +2504,7 @@
 	if (p->dir > XFRM_POLICY_OUT)
 		return NULL;
 
-	xp = xfrm_policy_alloc(net, GFP_KERNEL);
+	xp = xfrm_policy_alloc(net, GFP_ATOMIC);
 	if (xp == NULL) {
 		*dir = -ENOBUFS;
 		return NULL;