Re: [PATCH v3 2/2] rcu: Simplify the code logic of rcu_init_nohz()

[kernel test robot]

Hi Zhen,

Thank you for the patch! Perhaps something to improve:

[auto build test WARNING on paulmck-rcu/dev]
[also build test WARNING on linus/master v6.0-rc1 next-20220816]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch#_base_tree_information]

url:    https://github.com/intel-lab-lkp/linux/commits/Zhen-Lei/rcu-nocb-Delete-local-variable-need_rcu_nocb_mask-in-rcu_init_nohz/20220816-205131
base:   https://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu.git dev
config: x86_64-randconfig-a004-20220815 (https://download.01.org/0day-ci/archive/20220817/202208170309.j1yYU9wN-lkp@xxxxxxxxx/config)
compiler: gcc-11 (Debian 11.3.0-5) 11.3.0
reproduce (this is a W=1 build):
        # https://github.com/intel-lab-lkp/linux/commit/a1d5079765918764de3ff6e3e63fa2db7f7c14df
        git remote add linux-review https://github.com/intel-lab-lkp/linux
        git fetch --no-tags linux-review Zhen-Lei/rcu-nocb-Delete-local-variable-need_rcu_nocb_mask-in-rcu_init_nohz/20220816-205131
        git checkout a1d5079765918764de3ff6e3e63fa2db7f7c14df
        # save the config file
        mkdir build_dir && cp config build_dir/.config
        make W=1 O=build_dir ARCH=x86_64 SHELL=/bin/bash kernel/

If you fix the issue, kindly add following tag where applicable
Reported-by: kernel test robot <lkp@xxxxxxxxx>

All warnings (new ones prefixed by >>):

   In file included from kernel/rcu/tree.c:4801:
   kernel/rcu/tree_nocb.h: In function 'rcu_init_nohz':
>> kernel/rcu/tree_nocb.h:1216:17: warning: assignment discards 'const' qualifier from pointer target type [-Wdiscarded-qualifiers]
    1216 |         cpumask = cpu_possible_mask;
         |                 ^


vim +/const +1216 kernel/rcu/tree_nocb.h

  1208	
  1209	void __init rcu_init_nohz(void)
  1210	{
  1211		int cpu;
  1212		struct rcu_data *rdp;
  1213		struct cpumask *cpumask = NULL;
  1214	
  1215	#if defined(CONFIG_RCU_NOCB_CPU_DEFAULT_ALL)
> 1216		cpumask = cpu_possible_mask;
  1217	#elif defined(CONFIG_NO_HZ_FULL)
  1218		if (tick_nohz_full_running && !cpumask_empty(tick_nohz_full_mask))
  1219			cpumask = tick_nohz_full_mask;
  1220	#endif
  1221	
  1222		if (cpumask) {
  1223			if (!cpumask_available(rcu_nocb_mask)) {
  1224				if (!zalloc_cpumask_var(&rcu_nocb_mask, GFP_KERNEL)) {
  1225					pr_info("rcu_nocb_mask allocation failed, callback offloading disabled.\n");
  1226					return;
  1227				}
  1228			}
  1229	
  1230			cpumask_or(rcu_nocb_mask, rcu_nocb_mask, cpumask);
  1231		}
  1232	
  1233		if (!cpumask_available(rcu_nocb_mask))
  1234			return;
  1235	
  1236		if (!cpumask_subset(rcu_nocb_mask, cpu_possible_mask)) {
  1237			pr_info("\tNote: kernel parameter 'rcu_nocbs=', 'nohz_full', or 'isolcpus=' contains nonexistent CPUs.\n");
  1238			cpumask_and(rcu_nocb_mask, cpu_possible_mask,
  1239				    rcu_nocb_mask);
  1240		}
  1241		if (cpumask_empty(rcu_nocb_mask))
  1242			pr_info("\tOffload RCU callbacks from CPUs: (none).\n");
  1243		else
  1244			pr_info("\tOffload RCU callbacks from CPUs: %*pbl.\n",
  1245				cpumask_pr_args(rcu_nocb_mask));
  1246		if (rcu_nocb_poll)
  1247			pr_info("\tPoll for callbacks from no-CBs CPUs.\n");
  1248	
  1249		for_each_cpu(cpu, rcu_nocb_mask) {
  1250			rdp = per_cpu_ptr(&rcu_data, cpu);
  1251			if (rcu_segcblist_empty(&rdp->cblist))
  1252				rcu_segcblist_init(&rdp->cblist);
  1253			rcu_segcblist_offload(&rdp->cblist, true);
  1254			rcu_segcblist_set_flags(&rdp->cblist, SEGCBLIST_KTHREAD_CB | SEGCBLIST_KTHREAD_GP);
  1255			rcu_segcblist_clear_flags(&rdp->cblist, SEGCBLIST_RCU_CORE);
  1256		}
  1257		rcu_organize_nocb_kthreads();
  1258	}
  1259	

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