cgroup/cpuset: Convert cpuset_mutex to percpu_rwsem

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>

diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
index 846cbdb..e1a8d16 100644 (file)
--- a/kernel/cgroup/cpuset.c
+++ b/kernel/cgroup/cpuset.c
@@ -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;
@@ -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);
 
@@ -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();
 
        /*
@@ -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);
 }
 
 /**
@@ -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.
@@ -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;
@@ -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;
 }
 
@@ -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);
 }
 
 /*
@@ -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)
@@ -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 */
@@ -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;
@@ -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;
 }
 
@@ -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;
 
@@ -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;
 }
 
@@ -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;
 
@@ -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);
@@ -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;
 }
@@ -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))
@@ -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;
 }
 
@@ -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);
@@ -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)
@@ -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()) {
@@ -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);
 }
 
 /*
@@ -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));
@@ -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,
@@ -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
@@ -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;
        }
 
@@ -3073,7 +3075,7 @@ update_tasks:
                hotplug_update_tasks_legacy(cs, &new_cpus, &new_mems,
                                            cpus_updated, mems_updated);
 
-       mutex_unlock(&cpuset_mutex);
+       percpu_up_write(&cpuset_rwsem);
 }
 
 /**
@@ -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);
@@ -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) {