diff mbox series

[v4,27/33] mm: prevent userfaults to be handled under per-vma lock

Message ID 20230227173632.3292573-28-surenb@google.com (mailing list archive)
State Handled Elsewhere
Headers show
Series Per-VMA locks | expand

Commit Message

Suren Baghdasaryan Feb. 27, 2023, 5:36 p.m. UTC 
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@google.com>
Suggested-by: Peter Xu <peterx@redhat.com>
---
 mm/memory.c | 9 +++++++++
 1 file changed, 9 insertions(+)
diff mbox series

Patch

diff --git a/mm/memory.c b/mm/memory.c
index af3c2c59cd11..f734f80d28ca 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -5255,6 +5255,15 @@  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);