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sched/isolation: Force housekeeping if isolcpus and nohz_full don't leave any 

Currently the user can set up isolcpus and nohz_full in such a way that
leaves no housekeeping CPU (i.e. no CPU that is neither domain isolated
nor nohz full). This can be a problem for other subsystems (e.g. the
timer wheel imgration).

Prevent this configuration by invalidating the last setting in case the
union of isolcpus (domain) and nohz_full covers all CPUs.

Signed-off-by: Gabriele Monaco <gmonaco@redhat.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Waiman Long <longman@redhat.com>
Reviewed-by: Frederic Weisbecker <frederic@kernel.org>
Link: https://patch.msgid.link/20251120145653.296659-6-gmonaco@redhat.com
This commit is contained in:
Gabriele Monaco 2025-11-20 15:56:51 +01:00 committed by Thomas Gleixner
parent 22f8e41680
commit 185bccc797
1 changed files with 23 additions and 0 deletions
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23
kernel/sched/isolation.c
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@ -167,6 +167,29 @@ static int __init housekeeping_setup(char *str, unsigned long flags)
}
}
/*
* Check the combination of nohz_full and isolcpus=domain,
* necessary to avoid problems with the timer migration
* hierarchy. managed_irq is ignored by this check since it
* isn't considered in the timer migration logic.
*/
iter_flags = housekeeping.flags & (HK_FLAG_KERNEL_NOISE | HK_FLAG_DOMAIN);
type = find_first_bit(&iter_flags, HK_TYPE_MAX);
/*
* Pass the check if none of these flags were previously set or
* are not in the current selection.
*/
iter_flags = flags & (HK_FLAG_KERNEL_NOISE | HK_FLAG_DOMAIN);
first_cpu = (type == HK_TYPE_MAX || !iter_flags) ? 0 :
cpumask_first_and_and(cpu_present_mask,
housekeeping_staging, housekeeping.cpumasks[type]);
if (first_cpu >= min(nr_cpu_ids, setup_max_cpus)) {
pr_warn("Housekeeping: must include one present CPU "
"neither in nohz_full= nor in isolcpus=domain, "
"ignoring setting %s\n", str);
goto free_housekeeping_staging;
}
iter_flags = flags & ~housekeeping.flags;
for_each_set_bit(type, &iter_flags, HK_TYPE_MAX)