[CIFS] lock inode open file list in close in case racing with open

Harmless since it only protected turning off caching for the
inode, but cleaner to lock around this in case we have a close
racing with open.
Signed-off-by: Shaggy <shaggy@us.ibm.com>
CC: Cyrill Gorcunov <gorcunov@gmail.com>
Signed-off-by: Steve French <sfrench@us.ibm.com>

fs/cifs/file.c

@@ -545,6 +545,7 @@ int cifs_close(struct inode *inode, struct file *file)
 	} else
 		rc = -EBADF;
 
+	read_lock(&GlobalSMBSeslock);
 	if (list_empty(&(CIFS_I(inode)->openFileList))) {
 		cFYI(1, ("closing last open instance for inode %p", inode));
 		/* if the file is not open we do not know if we can cache info
@@ -552,6 +553,7 @@ int cifs_close(struct inode *inode, struct file *file)
 		CIFS_I(inode)->clientCanCacheRead = FALSE;
 		CIFS_I(inode)->clientCanCacheAll  = FALSE;
 	}
+	read_unlock(&GlobalSMBSeslock);
 	if ((rc == 0) && CIFS_I(inode)->write_behind_rc)
 		rc = CIFS_I(inode)->write_behind_rc;
 	FreeXid(xid);