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cgroup/cpuset: Convert cpuset_mutex to percpu_rwsem
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Holding cpuset_mutex means that cpusets are stable (only the holder can
make changes) and this is required for fixing a synchronization issue
between cpusets and scheduler core.  However, grabbing cpuset_mutex from
setscheduler() hotpath (as implemented in a later patch) is a no-go, as
it would create a bottleneck for tasks concurrently calling
setscheduler().

Convert cpuset_mutex to be a percpu_rwsem (cpuset_rwsem), so that
setscheduler() will then be able to read lock it and avoid concurrency
issues.

Tested-by: Dietmar Eggemann <dietmar.eggemann@arm.com>
Signed-off-by: Juri Lelli <juri.lelli@redhat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: bristot@redhat.com
Cc: claudio@evidence.eu.com
Cc: lizefan@huawei.com
Cc: longman@redhat.com
Cc: luca.abeni@santannapisa.it
Cc: mathieu.poirier@linaro.org
Cc: rostedt@goodmis.org
Cc: tj@kernel.org
Cc: tommaso.cucinotta@santannapisa.it
Link: https://lkml.kernel.org/r/20190719140000.31694-6-juri.lelli@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
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Juri Lelli authored and Ingo Molnar committed Jul 25, 2019
1 parent 59d06ce commit 1243dc5
Showing 1 changed file with 35 additions and 33 deletions.
68 changes: 35 additions & 33 deletions kernel/cgroup/cpuset.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -333,7 +333,7 @@ static struct cpuset top_cpuset = {
* guidelines for accessing subsystem state in kernel/cgroup.c
*/

static DEFINE_MUTEX(cpuset_mutex);
DEFINE_STATIC_PERCPU_RWSEM(cpuset_rwsem);
static DEFINE_SPINLOCK(callback_lock);

static struct workqueue_struct *cpuset_migrate_mm_wq;
Expand Down Expand Up @@ -913,7 +913,7 @@ static void rebuild_root_domains(void)
struct cpuset *cs = NULL;
struct cgroup_subsys_state *pos_css;

lockdep_assert_held(&cpuset_mutex);
percpu_rwsem_assert_held(&cpuset_rwsem);
lockdep_assert_cpus_held();
lockdep_assert_held(&sched_domains_mutex);

Expand Down Expand Up @@ -973,7 +973,7 @@ static void rebuild_sched_domains_locked(void)
cpumask_var_t *doms;
int ndoms;

lockdep_assert_held(&cpuset_mutex);
percpu_rwsem_assert_held(&cpuset_rwsem);
get_online_cpus();

/*
Expand Down Expand Up @@ -1005,9 +1005,9 @@ static void rebuild_sched_domains_locked(void)

void rebuild_sched_domains(void)
{
mutex_lock(&cpuset_mutex);
percpu_down_write(&cpuset_rwsem);
rebuild_sched_domains_locked();
mutex_unlock(&cpuset_mutex);
percpu_up_write(&cpuset_rwsem);
}

/**
Expand Down Expand Up @@ -1113,7 +1113,7 @@ static int update_parent_subparts_cpumask(struct cpuset *cpuset, int cmd,
int deleting; /* Moving cpus from subparts_cpus to effective_cpus */
bool part_error = false; /* Partition error? */

lockdep_assert_held(&cpuset_mutex);
percpu_rwsem_assert_held(&cpuset_rwsem);

/*
* The parent must be a partition root.
Expand Down Expand Up @@ -2101,7 +2101,7 @@ static int cpuset_can_attach(struct cgroup_taskset *tset)
cpuset_attach_old_cs = task_cs(cgroup_taskset_first(tset, &css));
cs = css_cs(css);

mutex_lock(&cpuset_mutex);
percpu_down_write(&cpuset_rwsem);

/* allow moving tasks into an empty cpuset if on default hierarchy */
ret = -ENOSPC;
Expand All @@ -2125,7 +2125,7 @@ static int cpuset_can_attach(struct cgroup_taskset *tset)
cs->attach_in_progress++;
ret = 0;
out_unlock:
mutex_unlock(&cpuset_mutex);
percpu_up_write(&cpuset_rwsem);
return ret;
}

Expand All @@ -2135,9 +2135,9 @@ static void cpuset_cancel_attach(struct cgroup_taskset *tset)

cgroup_taskset_first(tset, &css);

mutex_lock(&cpuset_mutex);
percpu_down_write(&cpuset_rwsem);
css_cs(css)->attach_in_progress--;
mutex_unlock(&cpuset_mutex);
percpu_up_write(&cpuset_rwsem);
}

/*
Expand All @@ -2160,7 +2160,7 @@ static void cpuset_attach(struct cgroup_taskset *tset)
cgroup_taskset_first(tset, &css);
cs = css_cs(css);

mutex_lock(&cpuset_mutex);
percpu_down_write(&cpuset_rwsem);

/* prepare for attach */
if (cs == &top_cpuset)
Expand Down Expand Up @@ -2214,7 +2214,7 @@ static void cpuset_attach(struct cgroup_taskset *tset)
if (!cs->attach_in_progress)
wake_up(&cpuset_attach_wq);

mutex_unlock(&cpuset_mutex);
percpu_up_write(&cpuset_rwsem);
}

/* The various types of files and directories in a cpuset file system */
Expand Down Expand Up @@ -2245,7 +2245,7 @@ static int cpuset_write_u64(struct cgroup_subsys_state *css, struct cftype *cft,
cpuset_filetype_t type = cft->private;
int retval = 0;

mutex_lock(&cpuset_mutex);
percpu_down_write(&cpuset_rwsem);
if (!is_cpuset_online(cs)) {
retval = -ENODEV;
goto out_unlock;
Expand Down Expand Up @@ -2281,7 +2281,7 @@ static int cpuset_write_u64(struct cgroup_subsys_state *css, struct cftype *cft,
break;
}
out_unlock:
mutex_unlock(&cpuset_mutex);
percpu_up_write(&cpuset_rwsem);
return retval;
}

Expand All @@ -2292,7 +2292,7 @@ static int cpuset_write_s64(struct cgroup_subsys_state *css, struct cftype *cft,
cpuset_filetype_t type = cft->private;
int retval = -ENODEV;

mutex_lock(&cpuset_mutex);
percpu_down_write(&cpuset_rwsem);
if (!is_cpuset_online(cs))
goto out_unlock;

Expand All @@ -2305,7 +2305,7 @@ static int cpuset_write_s64(struct cgroup_subsys_state *css, struct cftype *cft,
break;
}
out_unlock:
mutex_unlock(&cpuset_mutex);
percpu_up_write(&cpuset_rwsem);
return retval;
}

Expand Down Expand Up @@ -2344,7 +2344,7 @@ static ssize_t cpuset_write_resmask(struct kernfs_open_file *of,
kernfs_break_active_protection(of->kn);
flush_work(&cpuset_hotplug_work);

mutex_lock(&cpuset_mutex);
percpu_down_write(&cpuset_rwsem);
if (!is_cpuset_online(cs))
goto out_unlock;

Expand All @@ -2368,7 +2368,7 @@ static ssize_t cpuset_write_resmask(struct kernfs_open_file *of,

free_cpuset(trialcs);
out_unlock:
mutex_unlock(&cpuset_mutex);
percpu_up_write(&cpuset_rwsem);
kernfs_unbreak_active_protection(of->kn);
css_put(&cs->css);
flush_workqueue(cpuset_migrate_mm_wq);
Expand Down Expand Up @@ -2499,13 +2499,13 @@ static ssize_t sched_partition_write(struct kernfs_open_file *of, char *buf,
return -EINVAL;

css_get(&cs->css);
mutex_lock(&cpuset_mutex);
percpu_down_write(&cpuset_rwsem);
if (!is_cpuset_online(cs))
goto out_unlock;

retval = update_prstate(cs, val);
out_unlock:
mutex_unlock(&cpuset_mutex);
percpu_up_write(&cpuset_rwsem);
css_put(&cs->css);
return retval ?: nbytes;
}
Expand Down Expand Up @@ -2711,7 +2711,7 @@ static int cpuset_css_online(struct cgroup_subsys_state *css)
if (!parent)
return 0;

mutex_lock(&cpuset_mutex);
percpu_down_write(&cpuset_rwsem);

set_bit(CS_ONLINE, &cs->flags);
if (is_spread_page(parent))
Expand Down Expand Up @@ -2762,7 +2762,7 @@ static int cpuset_css_online(struct cgroup_subsys_state *css)
cpumask_copy(cs->effective_cpus, parent->cpus_allowed);
spin_unlock_irq(&callback_lock);
out_unlock:
mutex_unlock(&cpuset_mutex);
percpu_up_write(&cpuset_rwsem);
return 0;
}

Expand All @@ -2781,7 +2781,7 @@ static void cpuset_css_offline(struct cgroup_subsys_state *css)
{
struct cpuset *cs = css_cs(css);

mutex_lock(&cpuset_mutex);
percpu_down_write(&cpuset_rwsem);

if (is_partition_root(cs))
update_prstate(cs, 0);
Expand All @@ -2800,7 +2800,7 @@ static void cpuset_css_offline(struct cgroup_subsys_state *css)
cpuset_dec();
clear_bit(CS_ONLINE, &cs->flags);

mutex_unlock(&cpuset_mutex);
percpu_up_write(&cpuset_rwsem);
}

static void cpuset_css_free(struct cgroup_subsys_state *css)
Expand All @@ -2812,7 +2812,7 @@ static void cpuset_css_free(struct cgroup_subsys_state *css)

static void cpuset_bind(struct cgroup_subsys_state *root_css)
{
mutex_lock(&cpuset_mutex);
percpu_down_write(&cpuset_rwsem);
spin_lock_irq(&callback_lock);

if (is_in_v2_mode()) {
Expand All @@ -2825,7 +2825,7 @@ static void cpuset_bind(struct cgroup_subsys_state *root_css)
}

spin_unlock_irq(&callback_lock);
mutex_unlock(&cpuset_mutex);
percpu_up_write(&cpuset_rwsem);
}

/*
Expand Down Expand Up @@ -2867,6 +2867,8 @@ struct cgroup_subsys cpuset_cgrp_subsys = {

int __init cpuset_init(void)
{
BUG_ON(percpu_init_rwsem(&cpuset_rwsem));

BUG_ON(!alloc_cpumask_var(&top_cpuset.cpus_allowed, GFP_KERNEL));
BUG_ON(!alloc_cpumask_var(&top_cpuset.effective_cpus, GFP_KERNEL));
BUG_ON(!zalloc_cpumask_var(&top_cpuset.subparts_cpus, GFP_KERNEL));
Expand Down Expand Up @@ -2938,7 +2940,7 @@ hotplug_update_tasks_legacy(struct cpuset *cs,
is_empty = cpumask_empty(cs->cpus_allowed) ||
nodes_empty(cs->mems_allowed);

mutex_unlock(&cpuset_mutex);
percpu_up_write(&cpuset_rwsem);

/*
* Move tasks to the nearest ancestor with execution resources,
Expand All @@ -2948,7 +2950,7 @@ hotplug_update_tasks_legacy(struct cpuset *cs,
if (is_empty)
remove_tasks_in_empty_cpuset(cs);

mutex_lock(&cpuset_mutex);
percpu_down_write(&cpuset_rwsem);
}

static void
Expand Down Expand Up @@ -2998,14 +3000,14 @@ static void cpuset_hotplug_update_tasks(struct cpuset *cs, struct tmpmasks *tmp)
retry:
wait_event(cpuset_attach_wq, cs->attach_in_progress == 0);

mutex_lock(&cpuset_mutex);
percpu_down_write(&cpuset_rwsem);

/*
* We have raced with task attaching. We wait until attaching
* is finished, so we won't attach a task to an empty cpuset.
*/
if (cs->attach_in_progress) {
mutex_unlock(&cpuset_mutex);
percpu_up_write(&cpuset_rwsem);
goto retry;
}

Expand Down Expand Up @@ -3073,7 +3075,7 @@ static void cpuset_hotplug_update_tasks(struct cpuset *cs, struct tmpmasks *tmp)
hotplug_update_tasks_legacy(cs, &new_cpus, &new_mems,
cpus_updated, mems_updated);

mutex_unlock(&cpuset_mutex);
percpu_up_write(&cpuset_rwsem);
}

/**
Expand Down Expand Up @@ -3103,7 +3105,7 @@ static void cpuset_hotplug_workfn(struct work_struct *work)
if (on_dfl && !alloc_cpumasks(NULL, &tmp))
ptmp = &tmp;

mutex_lock(&cpuset_mutex);
percpu_down_write(&cpuset_rwsem);

/* fetch the available cpus/mems and find out which changed how */
cpumask_copy(&new_cpus, cpu_active_mask);
Expand Down Expand Up @@ -3153,7 +3155,7 @@ static void cpuset_hotplug_workfn(struct work_struct *work)
update_tasks_nodemask(&top_cpuset);
}

mutex_unlock(&cpuset_mutex);
percpu_up_write(&cpuset_rwsem);

/* if cpus or mems changed, we need to propagate to descendants */
if (cpus_updated || mems_updated) {
Expand Down

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