[PATCH RFC v2 4/4] mm/mempolicy: add nodes_empty check in SYSC_migrate_pages

As manpage of migrate_pages, the errno should be set to EINVAL when none
of the specified nodes contain memory. However, when new_nodes is null,
i.e. the specified nodes also do not have memory, as the following case:

	new_nodes = 0;
	old_nodes = 0xf;
	ret = migrate_pages(pid, old_nodes, new_nodes, MAX);

The ret will be 0 and no errno is set.

This patch is to add nodes_empty check to fix above case.

Signed-off-by: Yisheng Xie <redacted>
---
 mm/mempolicy.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/mm/mempolicy.c b/mm/mempolicy.c
index 8798ecb..58352cc 100644
--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c

@@ -1402,6 +1402,11 @@ static int copy_nodes_to_user(unsigned long __user *mask, unsigned long maxnode,
 	if (err)
 		goto out;
 
+	if (nodes_empty(*new)) {
+		err = -EINVAL;
+		goto out;
+	}
+
 	/* Find the mm_struct */
 	rcu_read_lock();
 	task = pid ? find_task_by_vpid(pid) : current;

-- 
1.7.12.4

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