a 'Text file busy' case caused by nfs server

[Wang Yugui <wangyugui@xxxxxxxxxxxx>]

Hi,

a 'Text file busy' case caused by nfs server.

nfs server: T7610, export /nfs 
	back-end filesystem: btrfs, xfs
nfs client1: T620, mount.nfs4 T7610:/nfs /nfs
nfs client2: T630, mount.nfs4 T7610:/nfs /nfs

linux kernel: 5.10.68, 5.15.0-rc3
	nfs server/client use the same kernel version

The steps to reproduce:
1, nfs client1
	cp /usr/bin/ls /nfs/ls.a
	cat /usr/bin/ls >/nfs/ls.b; chmod a+x /nfs/ls.b
	/nfs/ls.a >/dev/null
	/nfs/ls.b >/dev/null
	It works well.

2, nfs client2 
	/nfs/ls.a >/dev/null
	/nfs/ls.b >/dev/null
	it works well.

3, nfs server
	/nfs/ls.a >/dev/null
		-bash: /nfs/ls.a: Text file busy
		'Text file busy' happen
	/nfs/ls.b >/dev/null
		-bash: /nfs/ls.b: Text file busy
		'Text file busy' happen

	systemctl stop nfs-server.service
	/nfs/ls.a >/dev/null
	/nfs/ls.b >/dev/null
	it works well.

This 'Text file busy' happen when we exec/access the file through the
back-end filesystem directly, not through the nfs client/server.

so this is caused by some file handle(execute attr, and write mode?)
hold by nfs server?

Best Regards
Wang Yugui (wangyugui@xxxxxxxxxxxx)
2021/10/02