[tip:WIP.sched/core 101/144] drivers/char/nwbutton.c:134:3: error: implicit declaration of function 'kill_cad_pid'

[kbuild test robot]

tree:   https://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git WIP.sched/core
head:   f83f0b0647162b099f62e62c203b1cfb90b40239
commit: b1f67840abd11c21066791dab0ba74aac94fd178 [101/144] sched/headers, signals: Separate out task_struct::signal and task_struct::sighand types and accessors into <linux/sched/signal.h>
config: arm-footbridge_defconfig (attached as .config)
compiler: arm-linux-gnueabi-gcc (Debian 6.1.1-9) 6.1.1 20160705
reproduce:
        wget https://git.kernel.org/cgit/linux/kernel/git/wfg/lkp-tests.git/plain/sbin/make.cross -O ~/bin/make.cross
        chmod +x ~/bin/make.cross
        git checkout b1f67840abd11c21066791dab0ba74aac94fd178
        # save the attached .config to linux build tree
        make.cross ARCH=arm 

All errors (new ones prefixed by >>):

   drivers/char/nwbutton.c: In function 'button_sequence_finished':
>> drivers/char/nwbutton.c:134:3: error: implicit declaration of function 'kill_cad_pid' [-Werror=implicit-function-declaration]
      kill_cad_pid(SIGINT, 1); /* Ask init to reboot us */
      ^~~~~~~~~~~~
   cc1: some warnings being treated as errors

vim +/kill_cad_pid +134 drivers/char/nwbutton.c

^1da177e Linus Torvalds   2005-04-16  128   */
^1da177e Linus Torvalds   2005-04-16  129  
^1da177e Linus Torvalds   2005-04-16  130  static void button_sequence_finished (unsigned long parameters)
^1da177e Linus Torvalds   2005-04-16  131  {
990162f0 Arnd Bergmann    2016-01-25  132  	if (IS_ENABLED(CONFIG_NWBUTTON_REBOOT) &&
990162f0 Arnd Bergmann    2016-01-25  133  	    button_press_count == reboot_count)
9ec52099 Cedric Le Goater 2006-10-02 @134  		kill_cad_pid(SIGINT, 1);	/* Ask init to reboot us */
^1da177e Linus Torvalds   2005-04-16  135  	button_consume_callbacks (button_press_count);
^1da177e Linus Torvalds   2005-04-16  136  	bcount = sprintf (button_output_buffer, "%d\n", button_press_count);
^1da177e Linus Torvalds   2005-04-16  137  	button_press_count = 0;		/* Reset the button press counter */

:::::: The code at line 134 was first introduced by commit
:::::: 9ec52099e4b8678a60e9f93e41ad87885d64f3e6 [PATCH] replace cad_pid by a struct pid

:::::: TO: Cedric Le Goater <clg@xxxxxxxxxx>
:::::: CC: Linus Torvalds <torvalds@xxxxxxxxxxx>

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