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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

---
0-DAY kernel test infrastructure Open Source Technology Center
https://lists.01.org/pipermail/kbuild-all Intel Corporation
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