1 files changed, 11 insertions, 3 deletions

diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c
index 77c65a0bea34..864e0496cc1c 100644
--- a/fs/btrfs/extent_io.c
+++ b/fs/btrfs/extent_io.c
@@ -3885,6 +3885,12 @@ static void move_pages(struct page *dst_page, struct page *src_page,
         kunmap_atomic(dst_kaddr, KM_USER0);
 }
 
+static inline bool areas_overlap(unsigned long src, unsigned long dst, unsigned long len)
+{
+        unsigned long distance = (src > dst) ? src - dst : dst - src;
+        return distance < len;
+}
+
 static void copy_pages(struct page *dst_page, struct page *src_page,
                        unsigned long dst_off, unsigned long src_off,
                        unsigned long len)
@@ -3892,10 +3898,12 @@ static void copy_pages(struct page *dst_page, struct page *src_page,
         char *dst_kaddr = kmap_atomic(dst_page, KM_USER0);
         char *src_kaddr;
 
-        if (dst_page != src_page)
+        if (dst_page != src_page) {
                 src_kaddr = kmap_atomic(src_page, KM_USER1);
-        else
+        } else {
                 src_kaddr = dst_kaddr;
+                BUG_ON(areas_overlap(src_off, dst_off, len));
+        }
 
         memcpy(dst_kaddr + dst_off, src_kaddr + src_off, len);
         kunmap_atomic(dst_kaddr, KM_USER0);
@@ -3970,7 +3978,7 @@ void memmove_extent_buffer(struct extent_buffer *dst, unsigned long dst_offset,
                        "len %lu len %lu\n", dst_offset, len, dst->len);
                 BUG_ON(1);
         }
-        if (dst_offset < src_offset) {
+        if (!areas_overlap(src_offset, dst_offset, len)) {
                 memcpy_extent_buffer(dst, dst_offset, src_offset, len);
                 return;
         }