xfs: don't allocate COW extents when unsharing a hole

jira LE-3571
Rebuild_History Non-Buildable kernel-4.18.0-553.60.1.el8_10
commit-author Darrick J. Wong <djwong@kernel.org>
commit b8c4076

It doesn't make sense to allocate a COW extent when unsharing a hole
because holes cannot be shared.

Fixes: 1f1397b ("xfs: don't allocate into the data fork for an unshare request")
	Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Link: https://lore.kernel.org/r/172796813277.1131942.5486112889531210260.stgit@frogsfrogsfrogs
	Reviewed-by: Christoph Hellwig <hch@lst.de>
	Signed-off-by: Christian Brauner <brauner@kernel.org>
(cherry picked from commit b8c4076)
	Signed-off-by: Jonathan Maple <jmaple@ciq.com>

Author: PlaidCat

fs/xfs/xfs_iomap.c

@@ -673,7 +673,7 @@ imap_needs_cow(
 		return false;
 
 	/* when zeroing we don't have to COW holes or unwritten extents */
-	if (flags & IOMAP_ZERO) {
+	if (flags & (IOMAP_UNSHARE | IOMAP_ZERO)) {
 		if (!nimaps ||
 		    imap->br_startblock == HOLESTARTBLOCK ||
 		    imap->br_state == XFS_EXT_UNWRITTEN)