[PATCH 4/6] xfs: make xfs_file_aio_write_checks IOCB_NOWAIT-aware

[Dave Chinner <david@fromorbit.com>]

From: Christoph Hellwig <hch@lst.de>

Ensure we don't block on the iolock, or waiting for I/O in
xfs_file_aio_write_checks if the caller asked to avoid that.

Fixes: 29a5d29ec181 ("xfs: nowait aio support")
Signed-off-by: Christoph Hellwig <hch@lst.de>
---
 fs/xfs/xfs_file.c | 25 +++++++++++++++++++++----
 1 file changed, 21 insertions(+), 4 deletions(-)

diff --git a/fs/xfs/xfs_file.c b/fs/xfs/xfs_file.c
index 4eb4555516e4..512833ce1d41 100644
--- a/fs/xfs/xfs_file.c
+++ b/fs/xfs/xfs_file.c
@@ -341,7 +341,14 @@ xfs_file_aio_write_checks(
 	if (error <= 0)
 		return error;
 
-	error = xfs_break_layouts(inode, iolock, BREAK_WRITE);
+	if (iocb->ki_flags & IOCB_NOWAIT) {
+		error = break_layout(inode, false);
+		if (error == -EWOULDBLOCK)
+			error = -EAGAIN;
+	} else {
+		error = xfs_break_layouts(inode, iolock, BREAK_WRITE);
+	}
+
 	if (error)
 		return error;
 
@@ -352,7 +359,11 @@ xfs_file_aio_write_checks(
 	if (*iolock == XFS_IOLOCK_SHARED && !IS_NOSEC(inode)) {
 		xfs_iunlock(ip, *iolock);
 		*iolock = XFS_IOLOCK_EXCL;
-		xfs_ilock(ip, *iolock);
+		error = xfs_ilock_iocb(iocb, *iolock);
+		if (error) {
+			*iolock = 0;
+			return error;
+		}
 		goto restart;
 	}
 	/*
@@ -374,6 +385,10 @@ xfs_file_aio_write_checks(
 	isize = i_size_read(inode);
 	if (iocb->ki_pos > isize) {
 		spin_unlock(&ip->i_flags_lock);
+
+		if (iocb->ki_flags & IOCB_NOWAIT)
+			return -EAGAIN;
+
 		if (!drained_dio) {
 			if (*iolock == XFS_IOLOCK_SHARED) {
 				xfs_iunlock(ip, *iolock);
@@ -607,7 +622,8 @@ xfs_file_dio_aio_write(
 	trace_xfs_file_direct_write(ip, count, iocb->ki_pos);
 	ret = iomap_dio_rw(&args);
 out:
-	xfs_iunlock(ip, iolock);
+	if (iolock)
+		xfs_iunlock(ip, iolock);
 
 	/*
 	 * No fallback to buffered IO after short writes for XFS, direct I/O
@@ -646,7 +662,8 @@ xfs_file_dax_write(
 		error = xfs_setfilesize(ip, pos, ret);
 	}
 out:
-	xfs_iunlock(ip, iolock);
+	if (iolock)
+		xfs_iunlock(ip, iolock);
 	if (error)
 		return error;
 
-- 
2.28.0