3 files changed, 49 insertions, 0 deletions

diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c
index f173c5af6461..cdee391fc7bf 100644
--- a/fs/btrfs/extent_io.c
+++ b/fs/btrfs/extent_io.c
@@ -1257,6 +1257,39 @@ int unlock_extent(struct extent_io_tree *tree, u64 start, u64 end)
                                 GFP_NOFS);
 }
 
+int extent_range_clear_dirty_for_io(struct inode *inode, u64 start, u64 end)
+{
+        unsigned long index = start >> PAGE_CACHE_SHIFT;
+        unsigned long end_index = end >> PAGE_CACHE_SHIFT;
+        struct page *page;
+
+        while (index <= end_index) {
+                page = find_get_page(inode->i_mapping, index);
+                BUG_ON(!page); /* Pages should be in the extent_io_tree */
+                clear_page_dirty_for_io(page);
+                page_cache_release(page);
+                index++;
+        }
+        return 0;
+}
+
+int extent_range_redirty_for_io(struct inode *inode, u64 start, u64 end)
+{
+        unsigned long index = start >> PAGE_CACHE_SHIFT;
+        unsigned long end_index = end >> PAGE_CACHE_SHIFT;
+        struct page *page;
+
+        while (index <= end_index) {
+                page = find_get_page(inode->i_mapping, index);
+                BUG_ON(!page); /* Pages should be in the extent_io_tree */
+                account_page_redirty(page);
+                __set_page_dirty_nobuffers(page);
+                page_cache_release(page);
+                index++;
+        }
+        return 0;
+}
+
 /*
  * helper function to set both pages and extents in the tree writeback
  */
diff --git a/fs/btrfs/extent_io.h b/fs/btrfs/extent_io.h
index 6068a1985560..258c92156857 100644
--- a/fs/btrfs/extent_io.h
+++ b/fs/btrfs/extent_io.h
@@ -325,6 +325,8 @@ int map_private_extent_buffer(struct extent_buffer *eb, unsigned long offset,
                       unsigned long *map_len);
 int extent_range_uptodate(struct extent_io_tree *tree,
                           u64 start, u64 end);
+int extent_range_clear_dirty_for_io(struct inode *inode, u64 start, u64 end);
+int extent_range_redirty_for_io(struct inode *inode, u64 start, u64 end);
 int extent_clear_unlock_delalloc(struct inode *inode,
                                 struct extent_io_tree *tree,
                                 u64 start, u64 end, struct page *locked_page,
diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index 1f26888825e2..6a6e13c53086 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -353,6 +353,7 @@ static noinline int compress_file_range(struct inode *inode,
         int i;
         int will_compress;
         int compress_type = root->fs_info->compress_type;
+        int redirty = 0;
 
         /* if this is a small write inside eof, kick off a defrag */
         if ((end - start + 1) < 16 * 1024 &&
@@ -415,6 +416,17 @@ again:
                 if (BTRFS_I(inode)->force_compress)
                         compress_type = BTRFS_I(inode)->force_compress;
 
+                /*
+                 * we need to call clear_page_dirty_for_io on each
+                 * page in the range.  Otherwise applications with the file
+                 * mmap'd can wander in and change the page contents while
+                 * we are compressing them.
+                 *
+                 * If the compression fails for any reason, we set the pages
+                 * dirty again later on.
+                 */
+                extent_range_clear_dirty_for_io(inode, start, end);
+                redirty = 1;
                 ret = btrfs_compress_pages(compress_type,
                                            inode->i_mapping, start,
                                            total_compressed, pages,
@@ -554,6 +566,8 @@ cleanup_and_bail_uncompressed:
                         __set_page_dirty_nobuffers(locked_page);
                         /* unlocked later on in the async handlers */
                 }
+                if (redirty)
+                        extent_range_redirty_for_io(inode, start, end);
                 add_async_extent(async_cow, start, end - start + 1,
                                  0, NULL, 0, BTRFS_COMPRESS_NONE);
                 *num_added += 1;