selinux: use GFP_NOWAIT in the AVC kmem_caches

There is a strange __GFP_NOMEMALLOC usage pattern in SELinux,
specifically GFP_ATOMIC | __GFP_NOMEMALLOC which doesn't make much
sense.  GFP_ATOMIC on its own allows to access memory reserves while
__GFP_NOMEMALLOC dictates we cannot use memory reserves.  Replace this
with the much more sane GFP_NOWAIT in the AVC code as we can tolerate
memory allocation failures in that code.

Signed-off-by: Michal Hocko <[email protected]>
Acked-by: Mel Gorman <[email protected]>
Signed-off-by: Paul Moore <[email protected]>

Author: Michal Hocko

security/selinux/avc.c

@@ -348,27 +348,26 @@ static struct avc_xperms_decision_node
 	struct avc_xperms_decision_node *xpd_node;
 	struct extended_perms_decision *xpd;
 
-	xpd_node = kmem_cache_zalloc(avc_xperms_decision_cachep,
-				GFP_ATOMIC | __GFP_NOMEMALLOC);
+	xpd_node = kmem_cache_zalloc(avc_xperms_decision_cachep, GFP_NOWAIT);
 	if (!xpd_node)
 		return NULL;
 
 	xpd = &xpd_node->xpd;
 	if (which & XPERMS_ALLOWED) {
 		xpd->allowed = kmem_cache_zalloc(avc_xperms_data_cachep,
-						GFP_ATOMIC | __GFP_NOMEMALLOC);
+						GFP_NOWAIT);
 		if (!xpd->allowed)
 			goto error;
 	}
 	if (which & XPERMS_AUDITALLOW) {
 		xpd->auditallow = kmem_cache_zalloc(avc_xperms_data_cachep,
-						GFP_ATOMIC | __GFP_NOMEMALLOC);
+						GFP_NOWAIT);
 		if (!xpd->auditallow)
 			goto error;
 	}
 	if (which & XPERMS_DONTAUDIT) {
 		xpd->dontaudit = kmem_cache_zalloc(avc_xperms_data_cachep,
-						GFP_ATOMIC | __GFP_NOMEMALLOC);
+						GFP_NOWAIT);
 		if (!xpd->dontaudit)
 			goto error;
 	}
@@ -396,8 +395,7 @@ static struct avc_xperms_node *avc_xperms_alloc(void)
 {
 	struct avc_xperms_node *xp_node;
 
-	xp_node = kmem_cache_zalloc(avc_xperms_cachep,
-				GFP_ATOMIC|__GFP_NOMEMALLOC);
+	xp_node = kmem_cache_zalloc(avc_xperms_cachep, GFP_NOWAIT);
 	if (!xp_node)
 		return xp_node;
 	INIT_LIST_HEAD(&xp_node->xpd_head);
@@ -550,7 +548,7 @@ static struct avc_node *avc_alloc_node(void)
 {
 	struct avc_node *node;
 
-	node = kmem_cache_zalloc(avc_node_cachep, GFP_ATOMIC|__GFP_NOMEMALLOC);
+	node = kmem_cache_zalloc(avc_node_cachep, GFP_NOWAIT);
 	if (!node)
 		goto out;