Due to the possibility of handle_userfault dropping mmap_lock, avoid fault
handling under VMA lock and retry holding mmap_lock. This can be handled
more gracefully in the future.
Signed-off-by: Suren Baghdasaryan <surenb@xxxxxxxxxx>
Suggested-by: Peter Xu <peterx@xxxxxxxxxx>
---
mm/memory.c | 9 +++++++++
1 file changed, 9 insertions(+)
diff --git a/mm/memory.c b/mm/memory.c
index 33ecc850d3cb..55582c6fa2fd 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -5256,6 +5256,15 @@ struct vm_area_struct *lock_vma_under_rcu(struct mm_struct *mm,
if (!vma_start_read(vma))
goto inval;
+ /*
+ * Due to the possibility of userfault handler dropping mmap_lock, avoid
+ * it for now and fall back to page fault handling under mmap_lock.
+ */
+ if (userfaultfd_armed(vma)) {
+ vma_end_read(vma);
+ goto inval;
+ }
+
/* Check since vm_start/vm_end might change before we lock the VMA */
if (unlikely(address < vma->vm_start || address >= vma->vm_end)) {
vma_end_read(vma);
--
2.39.1
