ext4: move aio completion after unwritten extent conversion

This patch is to be applied upon Christoph's "direct-io: move aio_complete
into ->end_io" patch. It adds iocb and result fields to struct ext4_io_end_t,
so that we can call aio_complete from  ext4_end_io_nolock() after the extent
conversion has finished.

I have verified with Christoph's aio-dio test that used to fail after a few
runs on an original kernel but now succeeds on the patched kernel.

See http://thread.gmane.org/gmane.comp.file-systems.ext4/19659 for details.
Signed-off-by: Jiaying Zhang <jiayingz@google.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>

fs/ext4/ext4.h

@@ -170,13 +170,15 @@ struct mpage_da_data {
 };
 #define	EXT4_IO_UNWRITTEN	0x1
 typedef struct ext4_io_end {
-	struct list_head	list;		/* per-file finished AIO list */
+	struct list_head	list;		/* per-file finished IO list */
 	struct inode		*inode;		/* file being written to */
 	unsigned int		flag;		/* unwritten or not */
 	struct page		*page;		/* page struct for buffer write */
 	loff_t			offset;		/* offset in the file */
 	ssize_t			size;		/* size of the extent */
 	struct work_struct	work;		/* data work queue */
+	struct kiocb		*iocb;		/* iocb struct for AIO */
+	int			result;		/* error value for AIO */
 } ext4_io_end_t;
 
 /*

fs/ext4/inode.c

@@ -3668,6 +3668,8 @@ static int ext4_end_io_nolock(ext4_io_end_t *io)
 		return ret;
 	}
 
+	if (io->iocb)
+		aio_complete(io->iocb, io->result, 0);
 	/* clear the DIO AIO unwritten flag */
 	io->flag = 0;
 	return ret;
@@ -3767,6 +3769,8 @@ static ext4_io_end_t *ext4_init_io_end (struct inode *inode, gfp_t flags)
 		io->offset = 0;
 		io->size = 0;
 		io->page = NULL;
+		io->iocb = NULL;
+		io->result = 0;
 		INIT_WORK(&io->work, ext4_end_io_work);
 		INIT_LIST_HEAD(&io->list);
 	}
@@ -3796,12 +3800,18 @@ static void ext4_end_io_dio(struct kiocb *iocb, loff_t offset,
 	if (io_end->flag != EXT4_IO_UNWRITTEN){
 		ext4_free_io_end(io_end);
 		iocb->private = NULL;
-		goto out;
+out:
+		if (is_async)
+			aio_complete(iocb, ret, 0);
+		return;
 	}
 
 	io_end->offset = offset;
 	io_end->size = size;
-	io_end->flag = EXT4_IO_UNWRITTEN;
+	if (is_async) {
+		io_end->iocb = iocb;
+		io_end->result = ret;
+	}
 	wq = EXT4_SB(io_end->inode->i_sb)->dio_unwritten_wq;
 
 	/* queue the work to convert unwritten extents to written */
@@ -3813,9 +3823,6 @@ static void ext4_end_io_dio(struct kiocb *iocb, loff_t offset,
 	list_add_tail(&io_end->list, &ei->i_completed_io_list);
 	spin_unlock_irqrestore(&ei->i_completed_io_lock, flags);
 	iocb->private = NULL;
-out:
-	if (is_async)
-		aio_complete(iocb, ret, 0);
 }
 
 static void ext4_end_io_buffer_write(struct buffer_head *bh, int uptodate)