ext4: rip out DAX handling from direct IO path

Reads and writes for DAX inodes should no longer end up in direct IO
code. Rip out the support and add a warning.
Reviewed-by: Ross Zwisler <ross.zwisler@linux.intel.com>
Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>

fs/ext4/ext4.h

@@ -2452,8 +2452,6 @@ struct buffer_head *ext4_getblk(handle_t *, struct inode *, ext4_lblk_t, int);
 struct buffer_head *ext4_bread(handle_t *, struct inode *, ext4_lblk_t, int);
 int ext4_get_block_unwritten(struct inode *inode, sector_t iblock,
 			     struct buffer_head *bh_result, int create);
-int ext4_dax_get_block(struct inode *inode, sector_t iblock,
-		       struct buffer_head *bh_result, int create);
 int ext4_get_block(struct inode *inode, sector_t iblock,
 		   struct buffer_head *bh_result, int create);
 int ext4_dio_get_block(struct inode *inode, sector_t iblock,

fs/ext4/inode.c

@@ -3280,46 +3280,6 @@ static int ext4_releasepage(struct page *page, gfp_t wait)
 }
 
 #ifdef CONFIG_FS_DAX
-/*
- * Get block function for DAX IO and mmap faults. It takes care of converting
- * unwritten extents to written ones and initializes new / converted blocks
- * to zeros.
- */
-int ext4_dax_get_block(struct inode *inode, sector_t iblock,
-		       struct buffer_head *bh_result, int create)
-{
-	int ret;
-
-	ext4_debug("inode %lu, create flag %d\n", inode->i_ino, create);
-	if (!create)
-		return _ext4_get_block(inode, iblock, bh_result, 0);
-
-	ret = ext4_get_block_trans(inode, iblock, bh_result,
-				   EXT4_GET_BLOCKS_PRE_IO |
-				   EXT4_GET_BLOCKS_CREATE_ZERO);
-	if (ret < 0)
-		return ret;
-
-	if (buffer_unwritten(bh_result)) {
-		/*
-		 * We are protected by i_mmap_sem or i_mutex so we know block
-		 * cannot go away from under us even though we dropped
-		 * i_data_sem. Convert extent to written and write zeros there.
-		 */
-		ret = ext4_get_block_trans(inode, iblock, bh_result,
-					   EXT4_GET_BLOCKS_CONVERT |
-					   EXT4_GET_BLOCKS_CREATE_ZERO);
-		if (ret < 0)
-			return ret;
-	}
-	/*
-	 * At least for now we have to clear BH_New so that DAX code
-	 * doesn't attempt to zero blocks again in a racy way.
-	 */
-	clear_buffer_new(bh_result);
-	return 0;
-}
-
 static int ext4_iomap_begin(struct inode *inode, loff_t offset, loff_t length,
 			    unsigned flags, struct iomap *iomap)
 {
@@ -3473,14 +3433,6 @@ struct iomap_ops ext4_iomap_ops = {
 	.iomap_end		= ext4_iomap_end,
 };
 
-#else
-/* Just define empty function, it will never get called. */
-int ext4_dax_get_block(struct inode *inode, sector_t iblock,
-		       struct buffer_head *bh_result, int create)
-{
-	BUG();
-	return 0;
-}
 #endif
 
 static int ext4_end_io_dio(struct kiocb *iocb, loff_t offset,
@@ -3602,19 +3554,7 @@ static ssize_t ext4_direct_IO_write(struct kiocb *iocb, struct iov_iter *iter)
 	iocb->private = NULL;
 	if (overwrite)
 		get_block_func = ext4_dio_get_block_overwrite;
-	else if (IS_DAX(inode)) {
-		/*
-		 * We can avoid zeroing for aligned DAX writes beyond EOF. Other
-		 * writes need zeroing either because they can race with page
-		 * faults or because they use partial blocks.
-		 */
-		if (round_down(offset, 1<<inode->i_blkbits) >= inode->i_size &&
-		    ext4_aligned_io(inode, offset, count))
-			get_block_func = ext4_dio_get_block;
-		else
-			get_block_func = ext4_dax_get_block;
-		dio_flags = DIO_LOCKING;
-	} else if (!ext4_test_inode_flag(inode, EXT4_INODE_EXTENTS) ||
+	else if (!ext4_test_inode_flag(inode, EXT4_INODE_EXTENTS) ||
 		   round_down(offset, 1 << inode->i_blkbits) >= inode->i_size) {
 		get_block_func = ext4_dio_get_block;
 		dio_flags = DIO_LOCKING | DIO_SKIP_HOLES;
@@ -3628,14 +3568,9 @@ static ssize_t ext4_direct_IO_write(struct kiocb *iocb, struct iov_iter *iter)
 #ifdef CONFIG_EXT4_FS_ENCRYPTION
 	BUG_ON(ext4_encrypted_inode(inode) && S_ISREG(inode->i_mode));
 #endif
-	if (IS_DAX(inode)) {
-		ret = dax_do_io(iocb, inode, iter, get_block_func,
-				ext4_end_io_dio, dio_flags);
-	} else
-		ret = __blockdev_direct_IO(iocb, inode,
-					   inode->i_sb->s_bdev, iter,
-					   get_block_func,
-					   ext4_end_io_dio, NULL, dio_flags);
+	ret = __blockdev_direct_IO(iocb, inode, inode->i_sb->s_bdev, iter,
+				   get_block_func, ext4_end_io_dio, NULL,
+				   dio_flags);
 
 	if (ret > 0 && !overwrite && ext4_test_inode_state(inode,
 						EXT4_STATE_DIO_UNWRITTEN)) {
@@ -3704,6 +3639,7 @@ static ssize_t ext4_direct_IO_read(struct kiocb *iocb, struct iov_iter *iter)
 {
 	struct address_space *mapping = iocb->ki_filp->f_mapping;
 	struct inode *inode = mapping->host;
+	size_t count = iov_iter_count(iter);
 	ssize_t ret;
 
 	/*
@@ -3712,19 +3648,12 @@ static ssize_t ext4_direct_IO_read(struct kiocb *iocb, struct iov_iter *iter)
 	 * we are protected against page writeback as well.
 	 */
 	inode_lock_shared(inode);
-	if (IS_DAX(inode)) {
-		ret = dax_do_io(iocb, inode, iter, ext4_dio_get_block, NULL, 0);
-	} else {
-		size_t count = iov_iter_count(iter);
-
 	ret = filemap_write_and_wait_range(mapping, iocb->ki_pos,
 					   iocb->ki_pos + count);
 	if (ret)
 		goto out_unlock;
 	ret = __blockdev_direct_IO(iocb, inode, inode->i_sb->s_bdev,
-					   iter, ext4_dio_get_block,
-					   NULL, NULL, 0);
-	}
+				   iter, ext4_dio_get_block, NULL, NULL, 0);
 out_unlock:
 	inode_unlock_shared(inode);
 	return ret;
@@ -3753,6 +3682,10 @@ static ssize_t ext4_direct_IO(struct kiocb *iocb, struct iov_iter *iter)
 	if (ext4_has_inline_data(inode))
 		return 0;
 
+	/* DAX uses iomap path now */
+	if (WARN_ON_ONCE(IS_DAX(inode)))
+		return 0;
+
 	trace_ext4_direct_IO_enter(inode, offset, count, iov_iter_rw(iter));
 	if (iov_iter_rw(iter) == READ)
 		ret = ext4_direct_IO_read(iocb, iter);