linux-kernel - [rcu:dev.2018.10.03a 44/73] kernel/rcu/tree.c:2704:5: warning: 'max_cpu' may be used uninitialized in this function

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Date:   Mon, 8 Oct 2018 19:25:58 +0800
From:   kbuild test robot <lkp@...el.com>
To:     "Paul E. McKenney" <paulmck@...ux.ibm.com>
Cc:     kbuild-all@...org, linux-kernel@...r.kernel.org
Subject: [rcu:dev.2018.10.03a 44/73] kernel/rcu/tree.c:2704:5: warning:
 'max_cpu' may be used uninitialized in this function

tree:   https://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu.git dev.2018.10.03a
head:   ef44a26c84188888f97e5d7b3f8e4f8c0decd248
commit: 813f47a94e3b61439bba90340b532f3a6319d4f5 [44/73] rcu: Print per-CPU callback counts for forward-progress failures
config: x86_64-randconfig-x006-10081527 (attached as .config)
compiler: gcc-7 (Debian 7.3.0-1) 7.3.0
reproduce:
        git checkout 813f47a94e3b61439bba90340b532f3a6319d4f5
        # save the attached .config to linux build tree
        make ARCH=x86_64 

Note: it may well be a FALSE warning. FWIW you are at least aware of it now.
http://gcc.gnu.org/wiki/Better_Uninitialized_Warnings

All warnings (new ones prefixed by >>):

   kernel/rcu/tree.c: In function 'rcu_fwd_progress_check':
>> kernel/rcu/tree.c:2704:5: warning: 'max_cpu' may be used uninitialized in this function [-Wmaybe-uninitialized]
     if (max_cpu >= 0)
        ^
>> kernel/rcu/tree.c:2699:6: warning: 'max_cbs' may be used uninitialized in this function [-Wmaybe-uninitialized]
      if (cbs <= max_cbs)
         ^

vim +/max_cpu +2704 kernel/rcu/tree.c

  2670	
  2671	/*
  2672	 * Do a forward-progress check for rcutorture.  This is normally invoked
  2673	 * due to an OOM event.  The argument "j" gives the time period during
  2674	 * which rcutorture would like progress to have been made.
  2675	 */
  2676	void rcu_fwd_progress_check(unsigned long j)
  2677	{
  2678		unsigned long cbs;
  2679		int cpu;
  2680		unsigned long max_cbs;
  2681		int max_cpu;
  2682		struct rcu_data *rdp;
  2683	
  2684		if (rcu_gp_in_progress()) {
  2685			show_rcu_gp_kthreads();
  2686		} else {
  2687			preempt_disable();
  2688			rdp = this_cpu_ptr(&rcu_data);
  2689			rcu_check_gp_start_stall(rdp->mynode, rdp, j);
  2690			preempt_enable();
  2691		}
  2692		for_each_possible_cpu(cpu) {
  2693			cbs = rcu_get_n_cbs_cpu(cpu);
  2694			if (!cbs)
  2695				continue;
  2696			if (max_cpu < 0)
  2697				pr_info("%s: callbacks", __func__);
  2698			pr_cont(" %d: %lu", cpu, cbs);
> 2699			if (cbs <= max_cbs)
  2700				continue;
  2701			max_cbs = cbs;
  2702			max_cpu = cpu;
  2703		}
> 2704		if (max_cpu >= 0)
  2705			pr_cont("\n");
  2706	}
  2707	EXPORT_SYMBOL_GPL(rcu_fwd_progress_check);
  2708	

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