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