linux 5.13 kernel regression for NFS server

[Justin Piszcz]

Hello,

ISSUE: Can no longer mount NFS server(5.13) share.
WORKAROUND: Reverting back to the 5.13-rc7 kernel for the NFS server, all
clients can then mount the share.

Kernel 5.13 vs. 5.13-rc7 for x86_64

With Kernel 5.13-rc7:

## mount is successful (from multiple clients, phone, tv, other Linux
client)
# mount 192.168.1.2:/r1 /r1
#

With Kernel 5.13 (hangs from multiple clients, phone, tv, other Linux
client)

## mount hangs:
# mount 192.168.1.2:/r1 /r1

(strace output where it is hanging)
...
clone(child_stack=NULL,
flags=CLONE_CHILD_CLEARTID|CLONE_CHILD_SETTID|SIGCHLD,
child_tidptr=0x7f2285e303d0) = 1741
wait4(1741, 0x7ffeaab6ce08, 0, NULL)    = ? ERESTARTSYS (To be restarted if
SA_RESTART is set)
--- SIGWINCH {si_signo=SIGWINCH, si_code=SI_KERNEL} ---
wait4(1741,

No user changes in the kernel .config other than the comment for the version
text:

--- config-20210628.1624867695  2021-06-28 04:08:15.152781940 -0400
+++ config-20210628.1624867962  2021-06-28 04:12:42.591981706 -0400
@@ -1,6 +1,6 @@
 #
 # Automatically generated file; DO NOT EDIT.
-# Linux/x86 5.13.0-rc7 Kernel Configuration
+# Linux/x86 5.13.0 Kernel Configuration
 #
 CONFIG_CC_VERSION_TEXT="gcc (Debian 10.2.1-6) 10.2.1 20210110"
 CONFIG_CC_IS_GCC=y

Justin.