tree:   https://kernel.googlesource.com/pub/scm/linux/kernel/git/paulmck/linux-rcu.git dev.2019.09.23a
head:   97de53b94582c208ee239178b208b8e8b9472585
commit: 06b68648e6084488b79de47a2cfa307a1b9668b9 [65/77] rcu: Remove kfree_rcu() special casing and lazy-callback handling
config: x86_64-randconfig-c004-201938 (attached as .config)
compiler: gcc-7 (Debian 7.4.0-13) 7.4.0
reproduce:
        git checkout 06b68648e6084488b79de47a2cfa307a1b9668b9
        # save the attached .config to linux build tree
        make ARCH=x86_64 

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

All errors (new ones prefixed by >>):

   kernel//rcu/tree.c: In function 'kfree_rcu_work':
>> kernel//rcu/tree.c:2770:3: error: implicit declaration of function 'kfree'; did you mean 'kvfree'? [-Werror=implicit-function-declaration]
      kfree((void *)head - offset);
      ^~~~~
      kvfree
   cc1: some warnings being treated as errors

vim +2770 kernel//rcu/tree.c

  2739	
  2740	/*
  2741	 * This function is invoked in workqueue context after a grace period.
  2742	 * It frees all the objects queued on ->head_free.
  2743	 */
  2744	static void kfree_rcu_work(struct work_struct *work)
  2745	{
  2746		unsigned long flags;
  2747		struct rcu_head *head, *next;
  2748		struct kfree_rcu_cpu *krcp;
  2749		struct kfree_rcu_cpu_work *krwp;
  2750	
  2751		krwp = container_of(to_rcu_work(work),
  2752				    struct kfree_rcu_cpu_work, rcu_work);
  2753		krcp = krwp->krcp;
  2754		spin_lock_irqsave(&krcp->lock, flags);
  2755		head = krwp->head_free;
  2756		krwp->head_free = NULL;
  2757		spin_unlock_irqrestore(&krcp->lock, flags);
  2758	
  2759		// List "head" is now private, so traverse locklessly.
  2760		for (; head; head = next) {
  2761			unsigned long offset = (unsigned long)head->func;
  2762	
  2763			next = head->next;
  2764			// Potentially optimize with kfree_bulk in future.
  2765			debug_rcu_head_unqueue(head);
  2766			rcu_lock_acquire(&rcu_callback_map);
  2767			trace_rcu_invoke_kfree_callback(rcu_state.name, head, offset);
  2768	
  2769			/* Could be possible to optimize with kfree_bulk in future */
> 2770			kfree((void *)head - offset);
  2771	
  2772			rcu_lock_release(&rcu_callback_map);
  2773			cond_resched_tasks_rcu_qs();
  2774		}
  2775	}
  2776	

---
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