xfs: prepare xfs_break_layouts() to be called with XFS_MMAPLOCK_EXCL

In preparation for adding coordination between extent unmap operations
and busy dax-pages, update xfs_break_layouts() to permit it to be called
with the mmap lock held. This lock scheme will be required for
coordinating the break of 'dax layouts' (non-idle dax (ZONE_DEVICE)
pages mapped into the file's address space). Breaking dax layouts will
be added to xfs_break_layouts() in a future patch, for now this preps
the unmap call sites to take and hold XFS_MMAPLOCK_EXCL over the call to
xfs_break_layouts().

Cc: "Darrick J. Wong" <[e-mail]>
Cc: Ross Zwisler <[e-mail]>
Cc: Dave Chinner <[e-mail]>
Suggested-by: Christoph Hellwig <[e-mail]>
Reviewed-by: Christoph Hellwig <[e-mail]>
Reviewed-by: "Darrick J. Wong" <[e-mail]>
Signed-off-by: Dan Williams <[e-mail]>

fs/xfs/xfs_file.c

···
 	struct xfs_inode	*ip = XFS_I(inode);
 	long			error;
 	enum xfs_prealloc_flags	flags = 0;
-	uint			iolock = XFS_IOLOCK_EXCL;
+	uint			iolock = XFS_IOLOCK_EXCL | XFS_MMAPLOCK_EXCL;
 	loff_t			new_size = 0;
 	bool			do_file_insert = false;
 
···
 	error = xfs_break_layouts(inode, &iolock);
 	if (error)
 		goto out_unlock;
-
-	xfs_ilock(ip, XFS_MMAPLOCK_EXCL);
-	iolock |= XFS_MMAPLOCK_EXCL;
 
 	if (mode & FALLOC_FL_PUNCH_HOLE) {
 		error = xfs_free_file_space(ip, offset, len);

fs/xfs/xfs_ioctl.c

···
 	struct xfs_inode	*ip = XFS_I(inode);
 	struct iattr		iattr;
 	enum xfs_prealloc_flags	flags = 0;
-	uint			iolock = XFS_IOLOCK_EXCL;
+	uint			iolock = XFS_IOLOCK_EXCL | XFS_MMAPLOCK_EXCL;
 	int			error;
 
 	/*
···
 	error = xfs_break_layouts(inode, &iolock);
 	if (error)
 		goto out_unlock;
-
-	xfs_ilock(ip, XFS_MMAPLOCK_EXCL);
-	iolock |= XFS_MMAPLOCK_EXCL;
 
 	switch (bf->l_whence) {
 	case 0: /*SEEK_SET*/

fs/xfs/xfs_iops.c

···
 
 	if (iattr->ia_valid & ATTR_SIZE) {
 		struct xfs_inode	*ip = XFS_I(d_inode(dentry));
-		uint			iolock = XFS_IOLOCK_EXCL;
-
-		error = xfs_break_layouts(d_inode(dentry), &iolock);
-		if (error)
-			return error;
+		uint			iolock;
 
 		xfs_ilock(ip, XFS_MMAPLOCK_EXCL);
+		iolock = XFS_IOLOCK_EXCL | XFS_MMAPLOCK_EXCL;
+
+		error = xfs_break_layouts(d_inode(dentry), &iolock);
+		if (error) {
+			xfs_iunlock(ip, XFS_MMAPLOCK_EXCL);
+			return error;
+		}
+
 		error = xfs_vn_setattr_size(dentry, iattr);
 		xfs_iunlock(ip, XFS_MMAPLOCK_EXCL);
 	} else {

fs/xfs/xfs_pnfs.c

···
 	while ((error = break_layout(inode, false) == -EWOULDBLOCK)) {
 		xfs_iunlock(ip, *iolock);
 		error = break_layout(inode, true);
-		*iolock = XFS_IOLOCK_EXCL;
+		*iolock &= ~XFS_IOLOCK_SHARED;
+		*iolock |= XFS_IOLOCK_EXCL;
 		xfs_ilock(ip, *iolock);
 	}