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

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Since commit ff0ce721ec21 ("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: Juri Lelli <juri.lelli@redhat.com>
Closes: https://lore.kernel.org/lkml/ZyuUcJDPBln1BK1Y@jlelli-thinkpadt14gen4.remote.csb/
Signed-off-by: Waiman Long <longman@redhat.com>
Tested-by: Juri Lelli <juri.lelli@redhat.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
This commit is contained in:
Waiman Long 2024-11-09 21:50:22 -05:00 committed by Tejun Heo
parent bcd7012afd
commit a040c35128
1 changed files with 33 additions and 16 deletions
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49
kernel/cgroup/cpuset.c
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@ -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 @@ get_css:
}
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)
rebuild_sched_domains_locked();
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 @@ out:
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);
}