f2fs: use cow inode data when updating atomic write

Need to use cow inode data content instead of the one in the original
inode, when we try to write the already updated atomic write files.
Signed-off-by: Daeho Jeong <daehojeong@google.com>
Reviewed-by: Chao Yu <chao@kernel.org>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

fs/f2fs/data.c

@@ -3491,7 +3491,7 @@ static int __reserve_data_block(struct inode *inode, pgoff_t index,
 
 static int prepare_atomic_write_begin(struct f2fs_sb_info *sbi,
 			struct page *page, loff_t pos, unsigned int len,
-			block_t *blk_addr, bool *node_changed)
+			block_t *blk_addr, bool *node_changed, bool *use_cow)
 {
 	struct inode *inode = page->mapping->host;
 	struct inode *cow_inode = F2FS_I(inode)->cow_inode;
@@ -3505,10 +3505,12 @@ static int prepare_atomic_write_begin(struct f2fs_sb_info *sbi,
 
 	/* Look for the block in COW inode first */
 	err = __find_data_block(cow_inode, index, blk_addr);
-	if (err)
+	if (err) {
 		return err;
-	else if (*blk_addr != NULL_ADDR)
+	} else if (*blk_addr != NULL_ADDR) {
+		*use_cow = true;
 		return 0;
+	}
 
 	if (is_inode_flag_set(inode, FI_ATOMIC_REPLACE))
 		goto reserve_block;
@@ -3538,6 +3540,7 @@ static int f2fs_write_begin(struct file *file, struct address_space *mapping,
 	struct page *page = NULL;
 	pgoff_t index = ((unsigned long long) pos) >> PAGE_SHIFT;
 	bool need_balance = false;
+	bool use_cow = false;
 	block_t blkaddr = NULL_ADDR;
 	int err = 0;
 
@@ -3597,7 +3600,7 @@ static int f2fs_write_begin(struct file *file, struct address_space *mapping,
 
 	if (f2fs_is_atomic_file(inode))
 		err = prepare_atomic_write_begin(sbi, page, pos, len,
-					&blkaddr, &need_balance);
+					&blkaddr, &need_balance, &use_cow);
 	else
 		err = prepare_write_begin(sbi, page, pos, len,
 					&blkaddr, &need_balance);
@@ -3637,7 +3640,9 @@ static int f2fs_write_begin(struct file *file, struct address_space *mapping,
 			f2fs_handle_error(sbi, ERROR_INVALID_BLKADDR);
 			goto fail;
 		}
-		err = f2fs_submit_page_read(inode, page, blkaddr, 0, true);
+		err = f2fs_submit_page_read(use_cow ?
+				F2FS_I(inode)->cow_inode : inode, page,
+				blkaddr, 0, true);
 		if (err)
 			goto fail;