[PATCH 2/4 v2] mm: fix possible incorrect return value of migrate_pages() syscall

[Joonsoo Kim]

do_migrate_pages() can return the number of pages not migrated.
Because migrate_pages() syscall return this value directly,
migrate_pages() syscall may return the number of pages not migrated.
In fail case in migrate_pages() syscall, we should return error value.
So change err to -EBUSY

Additionally, Correct comment above do_migrate_pages()

Signed-off-by: Joonsoo Kim <js1304@xxxxxxxxx>
Cc: Sasha Levin <levinsasha928@xxxxxxxxx>
Cc: Christoph Lameter <cl@xxxxxxxxx>

diff --git a/mm/mempolicy.c b/mm/mempolicy.c
index 1d771e4..0732729 100644
--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c
@@ -948,7 +948,7 @@ static int migrate_to_node(struct mm_struct *mm, int source, int dest,
  * Move pages between the two nodesets so as to preserve the physical
  * layout as much as possible.
  *
- * Returns the number of page that could not be moved.
+ * Returns error or the number of pages not migrated.
  */
 int do_migrate_pages(struct mm_struct *mm, const nodemask_t *from,
 		     const nodemask_t *to, int flags)
@@ -1382,6 +1382,8 @@ SYSCALL_DEFINE4(migrate_pages, pid_t, pid, unsigned long, maxnode,
 
 	err = do_migrate_pages(mm, old, new,
 		capable(CAP_SYS_NICE) ? MPOL_MF_MOVE_ALL : MPOL_MF_MOVE);
+	if (err > 0)
+		err = -EBUSY;
 
 	mmput(mm);
 out:
-- 
1.7.9.5

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