Commit a040c351 authored by Waiman Long's avatar Waiman Long Committed by Tejun Heo
Browse files

cgroup/cpuset: Enforce at most one rebuild_sched_domains_locked() call per operation 



Since commit ff0ce721 ("cgroup/cpuset: Eliminate unncessary
sched domains rebuilds in hotplug"), there is only one
rebuild_sched_domains_locked() call per hotplug operation. However,
writing to the various cpuset control files may still casue more than
one rebuild_sched_domains_locked() call to happen in some cases.

Juri had found that two rebuild_sched_domains_locked() calls in
update_prstate(), one from update_cpumasks_hier() and another one from
update_partition_sd_lb() could cause cpuset partition to be created
with null total_bw for DL tasks. IOW, DL tasks may not be scheduled
correctly in such a partition.

A sample command sequence that can reproduce null total_bw is as
follows.

  # echo Y >/sys/kernel/debug/sched/verbose
  # echo +cpuset >/sys/fs/cgroup/cgroup.subtree_control
  # mkdir /sys/fs/cgroup/test
  # echo 0-7 > /sys/fs/cgroup/test/cpuset.cpus
  # echo 6-7 > /sys/fs/cgroup/test/cpuset.cpus.exclusive
  # echo root >/sys/fs/cgroup/test/cpuset.cpus.partition

Fix this double rebuild_sched_domains_locked() calls problem
by replacing existing calls with cpuset_force_rebuild() except
the rebuild_sched_domains_cpuslocked() call at the end of
cpuset_handle_hotplug(). Checking of the force_sd_rebuild flag is
now done at the end of cpuset_write_resmask() and update_prstate()
to determine if rebuild_sched_domains_locked() should be called or not.

The cpuset v1 code can still call rebuild_sched_domains_locked()
directly as double rebuild_sched_domains_locked() calls is not possible.

Reported-by: default avatarJuri Lelli <juri.lelli@redhat.com>
Closes: https://lore.kernel.org/lkml/ZyuUcJDPBln1BK1Y@jlelli-thinkpadt14gen4.remote.csb/


Signed-off-by: default avatarWaiman Long <longman@redhat.com>
Tested-by: default avatarJuri Lelli <juri.lelli@redhat.com>
Signed-off-by: default avatarTejun Heo <tj@kernel.org>
parent bcd7012a

kernel/cgroup/cpuset.c

+33 −16
Original line number Diff line number Diff line
@@ -84,9 +84,19 @@ static bool have_boot_isolcpus; 
static struct list_head remote_children;



/*

 * A flag to force sched domain rebuild at the end of an operation while

 * inhibiting it in the intermediate stages when set. Currently it is only

 * set in hotplug code.

 * A flag to force sched domain rebuild at the end of an operation.

 * It can be set in

 *  - update_partition_sd_lb()

 *  - remote_partition_check()

 *  - update_cpumasks_hier()

 *  - cpuset_update_flag()

 *  - cpuset_hotplug_update_tasks()

 *  - cpuset_handle_hotplug()

 *

 * Protected by cpuset_mutex (with cpus_read_lock held) or cpus_write_lock.

 *

 * Note that update_relax_domain_level() in cpuset-v1.c can still call

 * rebuild_sched_domains_locked() directly without using this flag.

 */

static bool force_sd_rebuild;
@@ -990,6 +1000,7 @@ void rebuild_sched_domains_locked(void) 


	lockdep_assert_cpus_held();

	lockdep_assert_held(&cpuset_mutex);

	force_sd_rebuild = false;



	/*

	 * If we have raced with CPU hotplug, return early to avoid
@@ -1164,8 +1175,8 @@ static void update_partition_sd_lb(struct cpuset *cs, int old_prs) 
			clear_bit(CS_SCHED_LOAD_BALANCE, &cs->flags);

	}



	if (rebuild_domains && !force_sd_rebuild)

		rebuild_sched_domains_locked();

	if (rebuild_domains)

		cpuset_force_rebuild();

}



/*
@@ -1512,8 +1523,8 @@ static void remote_partition_check(struct cpuset *cs, struct cpumask *newmask, 
			remote_partition_disable(child, tmp);

			disable_cnt++;

		}

	if (disable_cnt && !force_sd_rebuild)

		rebuild_sched_domains_locked();

	if (disable_cnt)

		cpuset_force_rebuild();

}



/*
@@ -2106,8 +2117,8 @@ static void update_cpumasks_hier(struct cpuset *cs, struct tmpmasks *tmp, 
	}

	rcu_read_unlock();



	if (need_rebuild_sched_domains && !force_sd_rebuild)

		rebuild_sched_domains_locked();

	if (need_rebuild_sched_domains)

		cpuset_force_rebuild();

}



/**
@@ -2726,9 +2737,13 @@ int cpuset_update_flag(cpuset_flagbits_t bit, struct cpuset *cs, 
	cs->flags = trialcs->flags;

	spin_unlock_irq(&callback_lock);



	if (!cpumask_empty(trialcs->cpus_allowed) && balance_flag_changed &&

	    !force_sd_rebuild)

	if (!cpumask_empty(trialcs->cpus_allowed) && balance_flag_changed) {

		if (!IS_ENABLED(CONFIG_CPUSETS_V1) ||

		    cgroup_subsys_on_dfl(cpuset_cgrp_subsys))

			cpuset_force_rebuild();

		else

			rebuild_sched_domains_locked();

	}



	if (spread_flag_changed)

		cpuset1_update_tasks_flags(cs);
@@ -2848,6 +2863,8 @@ static int update_prstate(struct cpuset *cs, int new_prs) 
	update_partition_sd_lb(cs, old_prs);



	notify_partition_change(cs, old_prs);

	if (force_sd_rebuild)

		rebuild_sched_domains_locked();

	free_cpumasks(NULL, &tmpmask);

	return 0;

}
@@ -3141,6 +3158,8 @@ ssize_t cpuset_write_resmask(struct kernfs_open_file *of, 
	}



	free_cpuset(trialcs);

	if (force_sd_rebuild)

		rebuild_sched_domains_locked();

out_unlock:

	mutex_unlock(&cpuset_mutex);

	cpus_read_unlock();
@@ -3885,11 +3904,9 @@ static void cpuset_handle_hotplug(void) 
		rcu_read_unlock();

	}



	/* rebuild sched domains if cpus_allowed has changed */

	if (force_sd_rebuild) {

		force_sd_rebuild = false;

	/* rebuild sched domains if necessary */

	if (force_sd_rebuild)

		rebuild_sched_domains_cpuslocked();

	}



	free_cpumasks(NULL, ptmp);

}