Re: [PATCH] sched/core: Don't mix isolcpus and housekeeping CPUs

[kbuild test robot]

Hi Srikar,

Thank you for the patch! Perhaps something to improve:

[auto build test WARNING on tip/sched/core]
[also build test WARNING on v4.19 next-20181019]
[if your patch is applied to the wrong git tree, please drop us a note to help improve the system]

url:    https://github.com/0day-ci/linux/commits/Srikar-Dronamraju/sched-core-Don-t-mix-isolcpus-and-housekeeping-CPUs/20181024-025019
config: i386-tinyconfig (attached as .config)
compiler: gcc-7 (Debian 7.3.0-1) 7.3.0
reproduce:
        # save the attached .config to linux build tree
        make ARCH=i386 

All warnings (new ones prefixed by >>):

   kernel/sched/core.c: In function 'sched_setaffinity':
>> kernel/sched/core.c:4783:10: warning: assignment discards 'const' qualifier from pointer target type [-Wdiscarded-qualifiers]
     hk_mask = housekeeping_cpumask(HK_FLAG_DOMAIN);
             ^

vim +/const +4783 kernel/sched/core.c

  4734	
  4735	long sched_setaffinity(pid_t pid, const struct cpumask *in_mask)
  4736	{
  4737		cpumask_var_t cpus_allowed, new_mask;
  4738		struct task_struct *p;
  4739		struct cpumask *hk_mask;
  4740		int retval;
  4741	
  4742		rcu_read_lock();
  4743	
  4744		p = find_process_by_pid(pid);
  4745		if (!p) {
  4746			rcu_read_unlock();
  4747			return -ESRCH;
  4748		}
  4749	
  4750		/* Prevent p going away */
  4751		get_task_struct(p);
  4752		rcu_read_unlock();
  4753	
  4754		if (p->flags & PF_NO_SETAFFINITY) {
  4755			retval = -EINVAL;
  4756			goto out_put_task;
  4757		}
  4758		if (!alloc_cpumask_var(&cpus_allowed, GFP_KERNEL)) {
  4759			retval = -ENOMEM;
  4760			goto out_put_task;
  4761		}
  4762		if (!alloc_cpumask_var(&new_mask, GFP_KERNEL)) {
  4763			retval = -ENOMEM;
  4764			goto out_free_cpus_allowed;
  4765		}
  4766		retval = -EPERM;
  4767		if (!check_same_owner(p)) {
  4768			rcu_read_lock();
  4769			if (!ns_capable(__task_cred(p)->user_ns, CAP_SYS_NICE)) {
  4770				rcu_read_unlock();
  4771				goto out_free_new_mask;
  4772			}
  4773			rcu_read_unlock();
  4774		}
  4775	
  4776		retval = security_task_setscheduler(p);
  4777		if (retval)
  4778			goto out_free_new_mask;
  4779	
  4780	
  4781		cpuset_cpus_allowed(p, cpus_allowed);
  4782		cpumask_and(new_mask, in_mask, cpus_allowed);
> 4783		hk_mask = housekeeping_cpumask(HK_FLAG_DOMAIN);
  4784	
  4785		/*
  4786		 * If the cpumask provided has CPUs that are part of isolated and
  4787		 * housekeeping_cpumask, then restrict it to just the CPUs that
  4788		 * are part of the housekeeping_cpumask.
  4789		 */
  4790		if (!cpumask_subset(new_mask, hk_mask) &&
  4791				cpumask_intersects(new_mask, hk_mask)) {
  4792			pr_info("pid %d: Mix of isolcpus and non-isolcpus provided\n",
  4793				       p->pid);
  4794			cpumask_and(new_mask, new_mask, hk_mask);
  4795		}
  4796	
  4797		/*
  4798		 * Since bandwidth control happens on root_domain basis,
  4799		 * if admission test is enabled, we only admit -deadline
  4800		 * tasks allowed to run on all the CPUs in the task's
  4801		 * root_domain.
  4802		 */
  4803	#ifdef CONFIG_SMP
  4804		if (task_has_dl_policy(p) && dl_bandwidth_enabled()) {
  4805			rcu_read_lock();
  4806			if (!cpumask_subset(task_rq(p)->rd->span, new_mask)) {
  4807				retval = -EBUSY;
  4808				rcu_read_unlock();
  4809				goto out_free_new_mask;
  4810			}
  4811			rcu_read_unlock();
  4812		}
  4813	#endif
  4814	again:
  4815		retval = __set_cpus_allowed_ptr(p, new_mask, true);
  4816	
  4817		if (!retval) {
  4818			cpuset_cpus_allowed(p, cpus_allowed);
  4819			if (!cpumask_subset(new_mask, cpus_allowed)) {
  4820				/*
  4821				 * We must have raced with a concurrent cpuset
  4822				 * update. Just reset the cpus_allowed to the
  4823				 * cpuset's cpus_allowed
  4824				 */
  4825				cpumask_copy(new_mask, cpus_allowed);
  4826				goto again;
  4827			}
  4828		}
  4829	out_free_new_mask:
  4830		free_cpumask_var(new_mask);
  4831	out_free_cpus_allowed:
  4832		free_cpumask_var(cpus_allowed);
  4833	out_put_task:
  4834		put_task_struct(p);
  4835		return retval;
  4836	}
  4837	

---
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