sched/isolation: Fix boot crash when maxcpus < first housekeeping CPU
housekeeping_setup() checks cpumask_intersects(present, online) to ensure that the kernel will have at least one housekeeping CPU after smp_init(), but this doesn't work if the maxcpus= kernel parameter limits the number of processors available after bootup. For example, a kernel with "maxcpus=2 nohz_full=0-2" parameters crashes at boot time on a virtual machine with 4 CPUs. Change housekeeping_setup() to use cpumask_first_and() and check that the returned CPU number is valid and less than setup_max_cpus. Another corner case is "nohz_full=0" on a machine with a single CPU or with the maxcpus=1 kernel argument. In this case non_housekeeping_mask is empty and tick_nohz_full_setup() makes no sense. And indeed, the kernel hits the WARN_ON(tick_nohz_full_running) in tick_sched_do_timer(). And how should the kernel interpret the "nohz_full=" parameter? It should be silently ignored, but currently cpulist_parse() happily returns the empty cpumask and this leads to the same problem. Change housekeeping_setup() to check cpumask_empty(non_housekeeping_mask) and do nothing in this case. Signed-off-by: Oleg Nesterov <oleg@redhat.com> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Signed-off-by: Ingo Molnar <mingo@kernel.org> Reviewed-by: Phil Auld <pauld@redhat.com> Acked-by: Frederic Weisbecker <frederic@kernel.org> Link: https://lore.kernel.org/r/20240413141746.GA10008@redhat.com
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@ -118,6 +118,7 @@ static void __init housekeeping_setup_type(enum hk_type type,
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static int __init housekeeping_setup(char *str, unsigned long flags)
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{
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cpumask_var_t non_housekeeping_mask, housekeeping_staging;
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unsigned int first_cpu;
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int err = 0;
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if ((flags & HK_FLAG_TICK) && !(housekeeping.flags & HK_FLAG_TICK)) {
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@ -138,7 +139,8 @@ static int __init housekeeping_setup(char *str, unsigned long flags)
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cpumask_andnot(housekeeping_staging,
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cpu_possible_mask, non_housekeeping_mask);
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if (!cpumask_intersects(cpu_present_mask, housekeeping_staging)) {
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first_cpu = cpumask_first_and(cpu_present_mask, housekeeping_staging);
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if (first_cpu >= nr_cpu_ids || first_cpu >= setup_max_cpus) {
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__cpumask_set_cpu(smp_processor_id(), housekeeping_staging);
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__cpumask_clear_cpu(smp_processor_id(), non_housekeeping_mask);
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if (!housekeeping.flags) {
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@ -147,6 +149,9 @@ static int __init housekeeping_setup(char *str, unsigned long flags)
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}
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}
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if (cpumask_empty(non_housekeeping_mask))
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goto free_housekeeping_staging;
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if (!housekeeping.flags) {
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/* First setup call ("nohz_full=" or "isolcpus=") */
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enum hk_type type;
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