mmap_region adds a newly created VMA into VMA tree and might modify it
afterwards before dropping the mmap_lock. This poses a problem for page
faults handled under per-VMA locks because they don't take the mmap_lock
and can stumble on this VMA while it's still being modified. Currently
this does not pose a problem since post-addition modifications are done
only for file-backed VMAs, which are not handled under per-VMA lock.
However, once support for handling file-backed page faults with per-VMA
locks is added, this will become a race.
Fix this by write-locking the VMA before inserting it into the VMA tree.
Other places where a new VMA is added into VMA tree do not modify it
after the insertion, so do not need the same locking.
Signed-off-by: Suren Baghdasaryan <surenb@xxxxxxxxxx>
---
mm/mmap.c | 2 ++
1 file changed, 2 insertions(+)
diff --git a/mm/mmap.c b/mm/mmap.c
index c66e4622a557..84c71431a527 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -2812,6 +2812,8 @@ unsigned long mmap_region(struct file *file, unsigned long addr,
if (vma->vm_file)
i_mmap_lock_write(vma->vm_file->f_mapping);
+ /* Lock the VMA since it is modified after insertion into VMA tree */
+ vma_start_write(vma);
vma_iter_store(&vmi, vma);
mm->map_count++;
if (vma->vm_file) {
--
2.41.0.255.g8b1d071c50-goog
