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@xxxxxxxxxx>
Closes: https://lore.kernel.org/lkml/ZyuUcJDPBln1BK1Y@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx/
Signed-off-by: Waiman Long <longman@xxxxxxxxxx>
---
kernel/cgroup/cpuset.c | 49 ++++++++++++++++++++++++++++--------------
1 file changed, 33 insertions(+), 16 deletions(-)
diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
index 565280193922..0d56a226c522 100644
--- a/kernel/cgroup/cpuset.c
+++ b/kernel/cgroup/cpuset.c
@@ -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)
- 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 @@ 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);
}
--
2.47.0
