MADV_PAGEOUT should fail on VMAs with the VM_DROPPABLE flag. While
MADV_PAGEOUT is intended to move anonymous pages to swap, VM_DROPPABLE
should not be swapped out.
There is an issue where using MADV_PAGEOUT on a VMA with the VM_DROPPABLE
flag behaves like MADV_DONTNEED, causing the pages to be dropped. This
could break the semantics of MADV_PAGEOUT, IMO.
So, let's add a check to detect the VM_DROPPABLE flag before doing
MADV_PAGEOUT and returns -EINVAL.
Fixes: 9651fcedf7b9 ("mm: add MAP_DROPPABLE for designating always lazily freeable mappings")
Signed-off-by: Mingzhe Yang <mingzhe.yang@xxxxxx>
Signed-off-by: Lance Yang <ioworker0@xxxxxxxxx>
---
mm/madvise.c | 2 ++
1 file changed, 2 insertions(+)
diff --git a/mm/madvise.c b/mm/madvise.c
index 49f3a75046f6..29d0234da8a1 100644
--- a/mm/madvise.c
+++ b/mm/madvise.c
@@ -1263,6 +1263,8 @@ static int madvise_vma_behavior(struct vm_area_struct *vma,
case MADV_COLD:
return madvise_cold(vma, prev, start, end);
case MADV_PAGEOUT:
+ if (vma->vm_flags & VM_DROPPABLE)
+ return -EINVAL;
return madvise_pageout(vma, prev, start, end);
case MADV_FREE:
case MADV_DONTNEED:
--
2.45.2
