1 files changed, 17 insertions, 5 deletions

diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c
index 39791b81ede7..5029f241908f 100644
--- a/mm/userfaultfd.c
+++ b/mm/userfaultfd.c
@@ -404,7 +404,8 @@ static __always_inline ssize_t __mcopy_atomic(struct mm_struct *dst_mm,
                                               unsigned long dst_start,
                                               unsigned long src_start,
                                               unsigned long len,
-                                              bool zeropage)
+                                              bool zeropage,
+                                              bool *mmap_changing)
 {
         struct vm_area_struct *dst_vma;
         ssize_t err;
@@ -431,6 +432,15 @@ retry:
         down_read(&dst_mm->mmap_sem);
 
         /*
+         * If memory mappings are changing because of non-cooperative
+         * operation (e.g. mremap) running in parallel, bail out and
+         * request the user to retry later
+         */
+        err = -EAGAIN;
+        if (mmap_changing && READ_ONCE(*mmap_changing))
+                goto out_unlock;
+
+        /*
          * Make sure the vma is not shared, that the dst range is
          * both valid and fully within a single existing vma.
          */
@@ -563,13 +573,15 @@ out:
 }
 
 ssize_t mcopy_atomic(struct mm_struct *dst_mm, unsigned long dst_start,
-                     unsigned long src_start, unsigned long len)
+                     unsigned long src_start, unsigned long len,
+                     bool *mmap_changing)
 {
-        return __mcopy_atomic(dst_mm, dst_start, src_start, len, false);
+        return __mcopy_atomic(dst_mm, dst_start, src_start, len, false,
+                              mmap_changing);
 }
 
 ssize_t mfill_zeropage(struct mm_struct *dst_mm, unsigned long start,
-                       unsigned long len)
+                       unsigned long len, bool *mmap_changing)
 {
-        return __mcopy_atomic(dst_mm, start, 0, len, true);
+        return __mcopy_atomic(dst_mm, start, 0, len, true, mmap_changing);
 }