[PATCH] mm/madvise: fix very subtle bug

[Lorenzo Stoakes]

With thanks to stress-ng --madvise :)

vma may have been updated (in the modify call in madvise_update_vma()), so
we can't assign prev = vma, we must first reassign vma to
madv_behavior->vma to account for this, before setting prev = vma.
---
 mm/madvise.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/madvise.c b/mm/madvise.c
index 4491bf080f55..c467ee42596f 100644
--- a/mm/madvise.c
+++ b/mm/madvise.c
@@ -1665,8 +1665,8 @@ int madvise_walk_vmas(struct madvise_behavior *madv_behavior)
 			vma = NULL;
 			madv_behavior->lock_dropped = false;
 		} else {
-			prev = vma;
 			vma = madv_behavior->vma;
+			prev = vma;
 		}

 		if (vma && range->end < vma->vm_end)
--
2.50.0