Clarify locking of cifs file and tcon structures and make more granular

Remove the global file_list_lock to simplify cifs/smb3 locking and
have spinlocks that more closely match the information they are
protecting.

Add new tcon->open_file_lock and file->file_info_lock spinlocks.
Locks continue to follow a heirachy,
	cifs_socket --> cifs_ses --> cifs_tcon --> cifs_file
where global tcp_ses_lock still protects socket and cifs_ses, while the
the newer locks protect the lower level structure's information
(tcon and cifs_file respectively).

CC: Stable <stable@vger.kernel.org>
Signed-off-by: Steve French <steve.french@primarydata.com>
Signed-off-by: Pavel Shilovsky <pshilov@microsoft.com>
Reviewed-by: Aurelien Aptel <aaptel@suse.com>
Reviewed-by: Germano Percossi <germano.percossi@citrix.com>

fs/cifs/cifsfs.c

@@ -1262,7 +1262,6 @@ init_cifs(void)
 	GlobalTotalActiveXid = 0;
 	GlobalMaxActiveXid = 0;
 	spin_lock_init(&cifs_tcp_ses_lock);
-	spin_lock_init(&cifs_file_list_lock);
 	spin_lock_init(&GlobalMid_Lock);
 
 	get_random_bytes(&cifs_lock_secret, sizeof(cifs_lock_secret));