5.9 nfsd update breaks v4.2 copy_file_range

[Murphy Zhou <jencce.kernel@xxxxxxxxx>]

Hi Bruce,

It's easy to reproduce by running multiple xfstests testcases on localhost
NFS shares. These testcases are:
  generic/430 generic/431 generic/432 generic/433 generic/565

This reproduces only on NFSv4.2.

Error log diff sample:

--- /dev/fd/63	2020-08-09 22:46:02.771745606 -0400
+++ results/generic/431.out.bad	2020-08-09 22:46:02.546745248 -0400
@@ -1,15 +1,22 @@
 QA output created by 431
 Create the original file and then copy
+cmp: EOF on /mnt/testdir/test-431/copy which is empty
 Original md5sums:
 ab56b4d92b40713acc5af89985d4b786  TEST_DIR/test-431/file
-ab56b4d92b40713acc5af89985d4b786  TEST_DIR/test-431/copy
+d41d8cd98f00b204e9800998ecf8427e  TEST_DIR/test-431/copy
 Small copies from various points in the original file
+cmp: EOF on /mnt/testdir/test-431/a which is empty
+cmp: EOF on /mnt/testdir/test-431/b which is empty
+cmp: EOF on /mnt/testdir/test-431/c which is empty
+cmp: EOF on /mnt/testdir/test-431/d which is empty
+cmp: EOF on /mnt/testdir/test-431/e which is empty
+cmp: EOF on /mnt/testdir/test-431/f which is empty
 md5sums after small copies
 ab56b4d92b40713acc5af89985d4b786  TEST_DIR/test-431/file
-0cc175b9c0f1b6a831c399e269772661  TEST_DIR/test-431/a
-92eb5ffee6ae2fec3ad71c777531578f  TEST_DIR/test-431/b
-4a8a08f09d37b73795649038408b5f33  TEST_DIR/test-431/c
-8277e0910d750195b448797616e091ad  TEST_DIR/test-431/d
-e1671797c52e15f763380b45e841ec32  TEST_DIR/test-431/e
-2015eb238d706eceefc784742928054f  TEST_DIR/test-431/f
+d41d8cd98f00b204e9800998ecf8427e  TEST_DIR/test-431/a
+d41d8cd98f00b204e9800998ecf8427e  TEST_DIR/test-431/b
+d41d8cd98f00b204e9800998ecf8427e  TEST_DIR/test-431/c
+d41d8cd98f00b204e9800998ecf8427e  TEST_DIR/test-431/d
+d41d8cd98f00b204e9800998ecf8427e  TEST_DIR/test-431/e
+d41d8cd98f00b204e9800998ecf8427e  TEST_DIR/test-431/f
 d41d8cd98f00b204e9800998ecf8427e  TEST_DIR/test-431/g

Bisecting shows the first "bad" commit is:

commit 94415b06eb8aed13481646026dc995f04a3a534a
Author: J. Bruce Fields <bfields@xxxxxxxxxx>
Date:   Tue Jul 7 09:28:05 2020 -0400

    nfsd4: a client's own opens needn't prevent delegations

I'm wondering if you're already aware of it, this simple report is for
your info.

Thanks.

-- 
Murphy