[rcu:rcu/dev 90/90] include/linux/bit_spinlock.h:29:4: error: implicit declaration of function 'cpu_relax'

[kbuild test robot]

tree:   https://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu.git rcu/dev
head:   894c3990aadbe57e0e87f9d18307fa2a4e27af7f
commit: 894c3990aadbe57e0e87f9d18307fa2a4e27af7f [90/90] fixup! rcu: Move ktime needs to rcutiny.h and remove ktime.h from rcupdate.h
config: sparc64-defconfig (attached as .config)
compiler: sparc64-linux-gnu-gcc (Debian 6.1.1-9) 6.1.1 20160705
reproduce:
        wget https://raw.githubusercontent.com/01org/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
        chmod +x ~/bin/make.cross
        git checkout 894c3990aadbe57e0e87f9d18307fa2a4e27af7f
        # save the attached .config to linux build tree
        make.cross ARCH=sparc64 

All errors (new ones prefixed by >>):

   In file included from include/linux/list_bl.h:5:0,
                    from include/linux/rculist_bl.h:7,
                    from include/linux/dcache.h:7,
                    from fs/notify/fsnotify.c:19:
   include/linux/bit_spinlock.h: In function 'bit_spin_lock':
>> include/linux/bit_spinlock.h:29:4: error: implicit declaration of function 'cpu_relax' [-Werror=implicit-function-declaration]
       cpu_relax();
       ^~~~~~~~~
   cc1: some warnings being treated as errors

vim +/cpu_relax +29 include/linux/bit_spinlock.h

fb1c8f93 Ingo Molnar    2005-09-10  13   * are significantly faster.
fb1c8f93 Ingo Molnar    2005-09-10  14   */
fb1c8f93 Ingo Molnar    2005-09-10  15  static inline void bit_spin_lock(int bitnum, unsigned long *addr)
fb1c8f93 Ingo Molnar    2005-09-10  16  {
fb1c8f93 Ingo Molnar    2005-09-10  17  	/*
fb1c8f93 Ingo Molnar    2005-09-10  18  	 * Assuming the lock is uncontended, this never enters
fb1c8f93 Ingo Molnar    2005-09-10  19  	 * the body of the outer loop. If it is contended, then
fb1c8f93 Ingo Molnar    2005-09-10  20  	 * within the inner loop a non-atomic test is used to
fb1c8f93 Ingo Molnar    2005-09-10  21  	 * busywait with less bus contention for a good time to
fb1c8f93 Ingo Molnar    2005-09-10  22  	 * attempt to acquire the lock bit.
fb1c8f93 Ingo Molnar    2005-09-10  23  	 */
fb1c8f93 Ingo Molnar    2005-09-10  24  	preempt_disable();
fb1c8f93 Ingo Molnar    2005-09-10  25  #if defined(CONFIG_SMP) || defined(CONFIG_DEBUG_SPINLOCK)
b8dc93cb Nick Piggin    2007-10-18  26  	while (unlikely(test_and_set_bit_lock(bitnum, addr))) {
fb1c8f93 Ingo Molnar    2005-09-10  27  		preempt_enable();
3dd2ee48 Linus Torvalds 2011-04-25  28  		do {
fb1c8f93 Ingo Molnar    2005-09-10 @29  			cpu_relax();
3dd2ee48 Linus Torvalds 2011-04-25  30  		} while (test_bit(bitnum, addr));
fb1c8f93 Ingo Molnar    2005-09-10  31  		preempt_disable();
fb1c8f93 Ingo Molnar    2005-09-10  32  	}
fb1c8f93 Ingo Molnar    2005-09-10  33  #endif
fb1c8f93 Ingo Molnar    2005-09-10  34  	__acquire(bitlock);
fb1c8f93 Ingo Molnar    2005-09-10  35  }
fb1c8f93 Ingo Molnar    2005-09-10  36  
fb1c8f93 Ingo Molnar    2005-09-10  37  /*

:::::: The code at line 29 was first introduced by commit
:::::: fb1c8f93d869b34cacb8b8932e2b83d96a19d720 [PATCH] spinlock consolidation

:::::: TO: Ingo Molnar <mingo@xxxxxxx>
:::::: CC: Linus Torvalds <torvalds@xxxxxxxxxxx>

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