[rcu:rcu/next 110/168] kernel/rcu/tree.c:3401:2: error: implicit declaration of function 'ASSERT_EXCLUSIVE_WRITER'

[kbuild test robot <lkp@intel.com>]

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tree:   https://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu.git rcu/next
head:   8aa63de65a79bd8c5c1c2b19452e35f58b043ac7
commit: e70e4b3e69ce8d3fdfc1f4bfe6ed27187e1a9016 [110/168] rcu: Mark rcu_state.ncpus to detect concurrent writes
config: arc-defconfig (attached as .config)
compiler: arc-elf-gcc (GCC) 9.2.0
reproduce:
        wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
        chmod +x ~/bin/make.cross
        git checkout e70e4b3e69ce8d3fdfc1f4bfe6ed27187e1a9016
        # save the attached .config to linux build tree
        GCC_VERSION=9.2.0 make.cross ARCH=arc 

If you fix the issue, kindly add following tag
Reported-by: kbuild test robot <lkp@intel.com>

Note: the rcu/rcu/next HEAD 8aa63de65a79bd8c5c1c2b19452e35f58b043ac7 builds fine.
      It only hurts bisectibility.

All errors (new ones prefixed by >>):

   kernel/rcu/tree.c: In function 'rcu_cpu_starting':
>> kernel/rcu/tree.c:3401:2: error: implicit declaration of function 'ASSERT_EXCLUSIVE_WRITER' [-Werror=implicit-function-declaration]
    3401 |  ASSERT_EXCLUSIVE_WRITER(rcu_state.ncpus);
         |  ^~~~~~~~~~~~~~~~~~~~~~~
   cc1: some warnings being treated as errors

vim +/ASSERT_EXCLUSIVE_WRITER +3401 kernel/rcu/tree.c

  3364	
  3365	/*
  3366	 * Mark the specified CPU as being online so that subsequent grace periods
  3367	 * (both expedited and normal) will wait on it.  Note that this means that
  3368	 * incoming CPUs are not allowed to use RCU read-side critical sections
  3369	 * until this function is called.  Failing to observe this restriction
  3370	 * will result in lockdep splats.
  3371	 *
  3372	 * Note that this function is special in that it is invoked directly
  3373	 * from the incoming CPU rather than from the cpuhp_step mechanism.
  3374	 * This is because this function must be invoked at a precise location.
  3375	 */
  3376	void rcu_cpu_starting(unsigned int cpu)
  3377	{
  3378		unsigned long flags;
  3379		unsigned long mask;
  3380		int nbits;
  3381		unsigned long oldmask;
  3382		struct rcu_data *rdp;
  3383		struct rcu_node *rnp;
  3384	
  3385		if (per_cpu(rcu_cpu_started, cpu))
  3386			return;
  3387	
  3388		per_cpu(rcu_cpu_started, cpu) = 1;
  3389	
  3390		rdp = per_cpu_ptr(&rcu_data, cpu);
  3391		rnp = rdp->mynode;
  3392		mask = rdp->grpmask;
  3393		raw_spin_lock_irqsave_rcu_node(rnp, flags);
  3394		WRITE_ONCE(rnp->qsmaskinitnext, rnp->qsmaskinitnext | mask);
  3395		oldmask = rnp->expmaskinitnext;
  3396		rnp->expmaskinitnext |= mask;
  3397		oldmask ^= rnp->expmaskinitnext;
  3398		nbits = bitmap_weight(&oldmask, BITS_PER_LONG);
  3399		/* Allow lockless access for expedited grace periods. */
  3400		smp_store_release(&rcu_state.ncpus, rcu_state.ncpus + nbits); /* ^^^ */
> 3401		ASSERT_EXCLUSIVE_WRITER(rcu_state.ncpus);
  3402		rcu_gpnum_ovf(rnp, rdp); /* Offline-induced counter wrap? */
  3403		rdp->rcu_onl_gp_seq = READ_ONCE(rcu_state.gp_seq);
  3404		rdp->rcu_onl_gp_flags = READ_ONCE(rcu_state.gp_flags);
  3405		if (rnp->qsmask & mask) { /* RCU waiting on incoming CPU? */
  3406			rcu_disable_urgency_upon_qs(rdp);
  3407			/* Report QS -after- changing ->qsmaskinitnext! */
  3408			rcu_report_qs_rnp(mask, rnp, rnp->gp_seq, flags);
  3409		} else {
  3410			raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
  3411		}
  3412		smp_mb(); /* Ensure RCU read-side usage follows above initialization. */
  3413	}
  3414	

---
0-DAY CI Kernel Test Service, Intel Corporation
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