cifs: Fix copy offload to flush destination region

Fix cifs_file_copychunk_range() to flush the destination region before
invalidating it to avoid potential loss of data should the copy fail, in
whole or in part, in some way.

Fixes: 7b2404a8 ("cifs: Fix flushing, invalidation and file size with copy_file_range()")
Signed-off-by: David Howells <dhowells@redhat.com>
cc: Steve French <stfrench@microsoft.com>
cc: Paulo Alcantara <pc@manguebit.com>
cc: Shyam Prasad N <nspmangalore@gmail.com>
cc: Rohith Surabattula <rohiths.msft@gmail.com>
cc: Matthew Wilcox <willy@infradead.org>
cc: Jeff Layton <jlayton@kernel.org>
cc: linux-cifs@vger.kernel.org
cc: linux-mm@kvack.org
cc: linux-fsdevel@vger.kernel.org
Signed-off-by: Steve French <stfrench@microsoft.com>

fs/smb/client/cifsfs.c

@@ -1341,7 +1341,6 @@ ssize_t cifs_file_copychunk_range(unsigned int xid,
 	struct cifsFileInfo *smb_file_target;
 	struct cifs_tcon *src_tcon;
 	struct cifs_tcon *target_tcon;
-	unsigned long long destend, fstart, fend;
 	ssize_t rc;
 
 	cifs_dbg(FYI, "copychunk range\n");
@@ -1391,25 +1390,13 @@ ssize_t cifs_file_copychunk_range(unsigned int xid,
 			goto unlock;
 	}
 
-	destend = destoff + len - 1;
-
-	/* Flush the folios at either end of the destination range to prevent
-	 * accidental loss of dirty data outside of the range.
+	/* Flush and invalidate all the folios in the destination region.  If
+	 * the copy was successful, then some of the flush is extra overhead,
+	 * but we need to allow for the copy failing in some way (eg. ENOSPC).
 	 */
-	fstart = destoff;
-	fend = destend;
-
-	rc = cifs_flush_folio(target_inode, destoff, &fstart, &fend, true);
+	rc = filemap_invalidate_inode(target_inode, true, destoff, destoff + len - 1);
 	if (rc)
 		goto unlock;
-	rc = cifs_flush_folio(target_inode, destend, &fstart, &fend, false);
-	if (rc)
-		goto unlock;
-	if (fend > target_cifsi->netfs.zero_point)
-		target_cifsi->netfs.zero_point = fend + 1;
-
-	/* Discard all the folios that overlap the destination region. */
-	truncate_inode_pages_range(&target_inode->i_data, fstart, fend);
 
 	fscache_invalidate(cifs_inode_cookie(target_inode), NULL,
 			   i_size_read(target_inode), 0);