[PATCH v9 6/8] cgroup/cpuset: Change cpuset_rwsem and hotplug lock order

Juri Lelli
2019-07-19T13:59:58Z

cpuset_rwsem is going to be acquired from sched_setscheduler() with a
following patch. There are however paths (e.g., spawn_ksoftirqd) in
which sched_scheduler() is eventually called while holding hotplug lock;
this creates a dependecy between hotplug lock (to be always acquired
first) and cpuset_rwsem (to be always acquired after hotplug lock).

Fix paths which currently take the two locks in the wrong order (after
a following patch is applied).

Signed-off-by: Juri Lelli <juri.lelli@redhat.com>
---
include/linux/cpuset.h | 8 ++++----
kernel/cgroup/cpuset.c | 22 +++++++++++++++++-----
2 files changed, 21 insertions(+), 9 deletions(-)

diff --git a/include/linux/cpuset.h b/include/linux/cpuset.h
index 934633a05d20..7f1478c26a33 100644
--- a/include/linux/cpuset.h
+++ b/include/linux/cpuset.h
@@ -40,14 +40,14 @@ static inline bool cpusets_enabled(void)

static inline void cpuset_inc(void)
{
- static_branch_inc(&cpusets_pre_enable_key);
- static_branch_inc(&cpusets_enabled_key);
+ static_branch_inc_cpuslocked(&cpusets_pre_enable_key);
+ static_branch_inc_cpuslocked(&cpusets_enabled_key);
}

static inline void cpuset_dec(void)
{
- static_branch_dec(&cpusets_enabled_key);
- static_branch_dec(&cpusets_pre_enable_key);
+ static_branch_dec_cpuslocked(&cpusets_enabled_key);
+ static_branch_dec_cpuslocked(&cpusets_pre_enable_key);
}

extern int cpuset_init(void);
diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
index 85491d09f3d3..93414ea63252 100644
--- a/kernel/cgroup/cpuset.c
+++ b/kernel/cgroup/cpuset.c
@@ -1026,8 +1026,8 @@ static void rebuild_sched_domains_locked(void)
cpumask_var_t *doms;
int ndoms;

+ lockdep_assert_cpus_held();
percpu_rwsem_assert_held(&cpuset_rwsem);
- get_online_cpus();

/*
* We have raced with CPU hotplug. Don't do anything to avoid
@@ -1036,19 +1036,17 @@ static void rebuild_sched_domains_locked(void)
*/
if (!top_cpuset.nr_subparts_cpus &&
!cpumask_equal(top_cpuset.effective_cpus, cpu_active_mask))
- goto out;
+ return;

if (top_cpuset.nr_subparts_cpus &&
!cpumask_subset(top_cpuset.effective_cpus, cpu_active_mask))
- goto out;
+ return;

/* Generate domain masks and attrs */
ndoms = generate_sched_domains(&doms, &attr);

/* Have scheduler rebuild the domains */
partition_and_rebuild_sched_domains(ndoms, doms, attr);
-out:
- put_online_cpus();
}
#else /* !CONFIG_SMP */
static void rebuild_sched_domains_locked(void)
@@ -1058,9 +1056,11 @@ static void rebuild_sched_domains_locked(void)

void rebuild_sched_domains(void)
{
+ get_online_cpus();
percpu_down_write(&cpuset_rwsem);
rebuild_sched_domains_locked();
percpu_up_write(&cpuset_rwsem);
+ put_online_cpus();
}

/**
@@ -2298,6 +2298,7 @@ static int cpuset_write_u64(struct cgroup_subsys_state *css, struct cftype *cft,
cpuset_filetype_t type = cft->private;
int retval = 0;

+ get_online_cpus();
percpu_down_write(&cpuset_rwsem);
if (!is_cpuset_online(cs)) {
retval = -ENODEV;
@@ -2335,6 +2336,7 @@ static int cpuset_write_u64(struct cgroup_subsys_state *css, struct cftype *cft,
}
out_unlock:
percpu_up_write(&cpuset_rwsem);
+ put_online_cpus();
return retval;
}

@@ -2345,6 +2347,7 @@ static int cpuset_write_s64(struct cgroup_subsys_state *css, struct cftype *cft,
cpuset_filetype_t type = cft->private;
int retval = -ENODEV;

+ get_online_cpus();
percpu_down_write(&cpuset_rwsem);
if (!is_cpuset_online(cs))
goto out_unlock;
@@ -2359,6 +2362,7 @@ static int cpuset_write_s64(struct cgroup_subsys_state *css, struct cftype *cft,
}
out_unlock:
percpu_up_write(&cpuset_rwsem);
+ put_online_cpus();
return retval;
}

@@ -2397,6 +2401,7 @@ static ssize_t cpuset_write_resmask(struct kernfs_open_file *of,
kernfs_break_active_protection(of->kn);
flush_work(&cpuset_hotplug_work);

+ get_online_cpus();
percpu_down_write(&cpuset_rwsem);
if (!is_cpuset_online(cs))
goto out_unlock;
@@ -2422,6 +2427,7 @@ static ssize_t cpuset_write_resmask(struct kernfs_open_file *of,
free_cpuset(trialcs);
out_unlock:
percpu_up_write(&cpuset_rwsem);
+ put_online_cpus();
kernfs_unbreak_active_protection(of->kn);
css_put(&cs->css);
flush_workqueue(cpuset_migrate_mm_wq);
@@ -2552,6 +2558,7 @@ static ssize_t sched_partition_write(struct kernfs_open_file *of, char *buf,
return -EINVAL;

css_get(&cs->css);
+ get_online_cpus();
percpu_down_write(&cpuset_rwsem);
if (!is_cpuset_online(cs))
goto out_unlock;
@@ -2559,6 +2566,7 @@ static ssize_t sched_partition_write(struct kernfs_open_file *of, char *buf,
retval = update_prstate(cs, val);
out_unlock:
percpu_up_write(&cpuset_rwsem);
+ put_online_cpus();
css_put(&cs->css);
return retval ?: nbytes;
}
@@ -2764,6 +2772,7 @@ static int cpuset_css_online(struct cgroup_subsys_state *css)
if (!parent)
return 0;

+ get_online_cpus();
percpu_down_write(&cpuset_rwsem);

set_bit(CS_ONLINE, &cs->flags);
@@ -2816,6 +2825,7 @@ static int cpuset_css_online(struct cgroup_subsys_state *css)
spin_unlock_irq(&callback_lock);
out_unlock:
percpu_up_write(&cpuset_rwsem);
+ put_online_cpus();
return 0;
}

@@ -2834,6 +2844,7 @@ static void cpuset_css_offline(struct cgroup_subsys_state *css)
{
struct cpuset *cs = css_cs(css);

+ get_online_cpus();
percpu_down_write(&cpuset_rwsem);

if (is_partition_root(cs))
@@ -2854,6 +2865,7 @@ static void cpuset_css_offline(struct cgroup_subsys_state *css)
clear_bit(CS_ONLINE, &cs->flags);

percpu_up_write(&cpuset_rwsem);
+ put_online_cpus();
}

static void cpuset_css_free(struct cgroup_subsys_state *css)
--
2.17.2