f2fs: fix redundant block allocation

In direct_IO path of f2fs_file_write_iter(),
1. f2fs_preallocate_blocks(F2FS_GET_BLOCK_PRE_DIO)
   -> allocate LBA X
2. f2fs_direct_IO()
   -> return 0;

Then,
f2fs_write_data_page() will allocate another LBA X+1.

This makes EIO triggered by HM-SMR.
Reviewed-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

fs/f2fs/data.c

@@ -658,6 +658,13 @@ static int __allocate_data_block(struct dnode_of_data *dn)
 	return 0;
 }
 
+static inline bool __force_buffered_io(struct inode *inode, int rw)
+{
+	return ((f2fs_encrypted_inode(inode) && S_ISREG(inode->i_mode)) ||
+			(rw == WRITE && test_opt(F2FS_I_SB(inode), LFS)) ||
+			F2FS_I_SB(inode)->s_ndevs);
+}
+
 int f2fs_preallocate_blocks(struct kiocb *iocb, struct iov_iter *from)
 {
 	struct inode *inode = file_inode(iocb->ki_filp);
@@ -677,7 +684,10 @@ int f2fs_preallocate_blocks(struct kiocb *iocb, struct iov_iter *from)
 		err = f2fs_convert_inline_inode(inode);
 		if (err)
 			return err;
-		return f2fs_map_blocks(inode, &map, 1, F2FS_GET_BLOCK_PRE_DIO);
+		return f2fs_map_blocks(inode, &map, 1,
+			__force_buffered_io(inode, WRITE) ?
+				F2FS_GET_BLOCK_PRE_AIO :
+				F2FS_GET_BLOCK_PRE_DIO);
 	}
 	if (iocb->ki_pos + iov_iter_count(from) > MAX_INLINE_DATA) {
 		err = f2fs_convert_inline_inode(inode);
@@ -1769,11 +1779,7 @@ static ssize_t f2fs_direct_IO(struct kiocb *iocb, struct iov_iter *iter)
 	if (err)
 		return err;
 
-	if (f2fs_encrypted_inode(inode) && S_ISREG(inode->i_mode))
-		return 0;
-	if (rw == WRITE && test_opt(F2FS_I_SB(inode), LFS))
-		return 0;
-	if (F2FS_I_SB(inode)->s_ndevs)
+	if (__force_buffered_io(inode, rw))
 		return 0;
 
 	trace_f2fs_direct_IO_enter(inode, offset, count, rw);