Re: kernel/sched/isolation.c:143 housekeeping_setup() warn: always true condition '(first_cpu >= 0) => (0-u32max >= 0)'

[Oleg Nesterov <oleg@redhat.com>]

Hello,

I am on PTO till May 9 without my working laptop, can't even read the source code.
I'll return to this when I'm back. CONFIG_SMP=n I guess.

On 04/30, kernel test robot wrote:
> tree:   https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master
> head:   98369dccd2f8e16bf4c6621053af7aa4821dcf8e
> commit: 257bf89d84121280904800acd25cc2c444c717ae sched/isolation: Fix boot crash when maxcpus < first housekeeping CPU
> date:   2 days ago
> config: xtensa-randconfig-r081-20240429 (https://download.01.org/0day-ci/archive/20240430/202404300915.WNvfwBz3-lkp@intel.com/config)
> compiler: xtensa-linux-gcc (GCC) 13.2.0
> 
> If you fix the issue in a separate patch/commit (i.e. not just a new version of
> the same patch/commit), kindly add following tags
> | Reported-by: kernel test robot <lkp@intel.com>
> | Closes: https://lore.kernel.org/oe-kbuild-all/202404300915.WNvfwBz3-lkp@intel.com/
> 
> New smatch warnings:
> kernel/sched/isolation.c:143 housekeeping_setup() warn: always true condition '(first_cpu >= 0) => (0-u32max >= 0)'
> 
> Old smatch warnings:
> arch/xtensa/include/asm/thread_info.h:97 current_thread_info() warn: inconsistent indenting
> 
> vim +143 kernel/sched/isolation.c
> 
>    117	
>    118	static int __init housekeeping_setup(char *str, unsigned long flags)
>    119	{
>    120		cpumask_var_t non_housekeeping_mask, housekeeping_staging;
>    121		unsigned int first_cpu;
>    122		int err = 0;
>    123	
>    124		if ((flags & HK_FLAG_TICK) && !(housekeeping.flags & HK_FLAG_TICK)) {
>    125			if (!IS_ENABLED(CONFIG_NO_HZ_FULL)) {
>    126				pr_warn("Housekeeping: nohz unsupported."
>    127					" Build with CONFIG_NO_HZ_FULL\n");
>    128				return 0;
>    129			}
>    130		}
>    131	
>    132		alloc_bootmem_cpumask_var(&non_housekeeping_mask);
>    133		if (cpulist_parse(str, non_housekeeping_mask) < 0) {
>    134			pr_warn("Housekeeping: nohz_full= or isolcpus= incorrect CPU range\n");
>    135			goto free_non_housekeeping_mask;
>    136		}
>    137	
>    138		alloc_bootmem_cpumask_var(&housekeeping_staging);
>    139		cpumask_andnot(housekeeping_staging,
>    140			       cpu_possible_mask, non_housekeeping_mask);
>    141	
>    142		first_cpu = cpumask_first_and(cpu_present_mask, housekeeping_staging);
>  > 143		if (first_cpu >= nr_cpu_ids || first_cpu >= setup_max_cpus) {
>    144			__cpumask_set_cpu(smp_processor_id(), housekeeping_staging);
>    145			__cpumask_clear_cpu(smp_processor_id(), non_housekeeping_mask);
>    146			if (!housekeeping.flags) {
>    147				pr_warn("Housekeeping: must include one present CPU, "
>    148					"using boot CPU:%d\n", smp_processor_id());
>    149			}
>    150		}
>    151	
>    152		if (cpumask_empty(non_housekeeping_mask))
>    153			goto free_housekeeping_staging;
>    154	
>    155		if (!housekeeping.flags) {
>    156			/* First setup call ("nohz_full=" or "isolcpus=") */
>    157			enum hk_type type;
>    158	
>    159			for_each_set_bit(type, &flags, HK_TYPE_MAX)
>    160				housekeeping_setup_type(type, housekeeping_staging);
>    161		} else {
>    162			/* Second setup call ("nohz_full=" after "isolcpus=" or the reverse) */
>    163			enum hk_type type;
>    164			unsigned long iter_flags = flags & housekeeping.flags;
>    165	
>    166			for_each_set_bit(type, &iter_flags, HK_TYPE_MAX) {
>    167				if (!cpumask_equal(housekeeping_staging,
>    168						   housekeeping.cpumasks[type])) {
>    169					pr_warn("Housekeeping: nohz_full= must match isolcpus=\n");
>    170					goto free_housekeeping_staging;
>    171				}
>    172			}
>    173	
>    174			iter_flags = flags & ~housekeeping.flags;
>    175	
>    176			for_each_set_bit(type, &iter_flags, HK_TYPE_MAX)
>    177				housekeeping_setup_type(type, housekeeping_staging);
>    178		}
>    179	
>    180		if ((flags & HK_FLAG_TICK) && !(housekeeping.flags & HK_FLAG_TICK))
>    181			tick_nohz_full_setup(non_housekeeping_mask);
>    182	
>    183		housekeeping.flags |= flags;
>    184		err = 1;
>    185	
>    186	free_housekeeping_staging:
>    187		free_bootmem_cpumask_var(housekeeping_staging);
>    188	free_non_housekeeping_mask:
>    189		free_bootmem_cpumask_var(non_housekeeping_mask);
>    190	
>    191		return err;
>    192	}
>    193	
> 
> -- 
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>