Description of problem:
sunrpc.tcp_max_slot_table_entries值较低时，kill xprt task大概率导致nfs夯住

Version-Release number of selected component (if applicable):
4.19.91-25.1.al7.x86_64

How reproducible:


Steps to Reproduce:
1.
echo "options sunrpc tcp_slot_table_entries=2" >> /etc/modprobe.d/sunrpc.conf
echo "options sunrpc tcp_max_slot_table_entries=2" >>  /etc/modprobe.d/sunrpc.conf
and reboot

2.remount nfsv3: sudo mount -t nfs -o vers=3,nolock,proto=tcp 127.0.0.1:/root/nfs_server/ /root/nfs_client/

3.Run case
# cat case.sh 
while true
do
    ls &
done &

while true
do
    killall ls
done &

[root@cuibixuan nfs_client]# cd /root/nfs_client/; sh case.sh

4. Run 'killall sh' to kill case after waiting 10 seconds

5. The nfs hang and xprt->state is 0x212(XPRT_CONGESTED):
[root@cuibixuan sunrpc]# cat /sys/kernel/debug/sunrpc/rpc_xprt/4/info 
netid: tcp
addr:  127.0.0.1
port:  2049
state: 0x212

[root@cuibixuan sunrpc]# cat /sys/kernel/debug/sunrpc/rpc_clnt/4/tasks 
  155 0080    -11 0x4 0x0        0 rpc_default_ops [sunrpc] nfsv3 GETATTR a:call_reserveresult [sunrpc] q:xprt_backlog
15418 0080    -11 0x4 0x0        0 rpc_default_ops [sunrpc] nfsv3 GETATTR a:call_reserveresult [sunrpc] q:xprt_backlog

6. Enable ftrace
 # echo 1 > /sys/kernel/debug/tracing/events/sunrpc/enable
 # cat /sys/kernel/debug/tracing/trace
	      ...
              ls-18792 [001] ....   668.541062: rpc_task_run_action: task:28885@4 flags=0080 state=0005 status=0 action=call_start [sunrpc]
              ls-18792 [001] ....   668.541063: rpc_request: task:28885@4 nfsv3 GETATTR (sync)
              ls-18792 [001] ....   668.541063: rpc_task_run_action: task:28885@4 flags=0080 state=0005 status=0 action=call_reserve [sunrpc]
              ls-18792 [001] ....   668.541065: rpc_task_sleep: task:28885@4 flags=0080 state=0005 status=-11 timeout=0 queue=xprt_backlog
              ls-18792 [000] ....   670.815066: rpc_task_wakeup: task:28885@4 flags=0180 state=0006 status=-512 timeout=0 queue=xprt_backlog
              ls-18792 [000] ....   670.815069: rpc_task_run_action: task:28885@4 flags=0180 state=0005 status=-512 action=rpc_exit_task [sunrpc]
              ls-18846 [001] ....   682.302970: rpc_task_begin: task:28886@4 flags=0080 state=0004 status=0 action=          (null)
              ls-18846 [001] ....   682.302972: rpc_task_run_action: task:28886@4 flags=0080 state=0005 status=0 action=call_start [sunrpc]
              ls-18846 [001] ....   682.302973: rpc_request: task:28886@4 nfsv3 GETATTR (sync)
              ls-18846 [001] ....   682.302973: rpc_task_run_action: task:28886@4 flags=0080 state=0005 status=0 action=call_reserve [sunrpc]
              ls-18846 [001] ....   682.302974: rpc_task_sleep: task:28886@4 flags=0080 state=0005 status=-11 timeout=0 queue=xprt_backlog
              ls-18846 [000] ....   684.690924: rpc_task_wakeup: task:28886@4 flags=0180 state=0006 status=-512 timeout=0 queue=xprt_backlog
              ls-18846 [000] ....   684.690928: rpc_task_run_action: task:28886@4 flags=0180 state=0005 status=-512 action=rpc_exit_task [sunrpc]

Actual results:
nfs夯住，命令卡住。
xprt->state is 0x212(XPRT_CONGESTED):
[root@cuibixuan sunrpc]# cat /sys/kernel/debug/sunrpc/rpc_xprt/4/info 
netid: tcp
addr:  127.0.0.1
port:  2049
state: 0x212

[root@cuibixuan sunrpc]# cat /sys/kernel/debug/sunrpc/rpc_clnt/4/tasks 
  155 0080    -11 0x4 0x0        0 rpc_default_ops [sunrpc] nfsv3 GETATTR a:call_reserveresult [sunrpc] q:xprt_backlog
15418 0080    -11 0x4 0x0        0 rpc_default_ops [sunrpc] nfsv3 GETATTR a:call_reserveresult [sunrpc] q:xprt_backlog


Expected results:
nfs不会夯住，任务正常退出

Additional info: