Commit 185bccc7 authored by Gabriele Monaco's avatar Gabriele Monaco Committed by Thomas Gleixner
Browse files

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: default avatarGabriele Monaco <gmonaco@redhat.com>
Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
Reviewed-by: default avatarWaiman Long <longman@redhat.com>
Reviewed-by: default avatarFrederic Weisbecker <frederic@kernel.org>
Link: https://patch.msgid.link/20251120145653.296659-6-gmonaco@redhat.com
parent 22f8e416

kernel/sched/isolation.c

+23 −0
Original line number Diff line number Diff line
@@ -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)