Commit d74b27d6 authored by Juri Lelli's avatar Juri Lelli Committed by Ingo Molnar
Browse files

cgroup/cpuset: Change cpuset_rwsem and hotplug lock order 



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).

Tested-by: default avatarDietmar Eggemann <dietmar.eggemann@arm.com>
Signed-off-by: default avatarJuri Lelli <juri.lelli@redhat.com>
Signed-off-by: default avatarPeter 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/20190719140000.31694-7-juri.lelli@redhat.com


Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
parent 1243dc51

include/linux/cpuset.h

+4 −4
Original line number Diff line number Diff line
@@ -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);

kernel/cgroup/cpuset.c

+17 −5
Original line number Diff line number Diff line
@@ -973,8 +973,8 @@ 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
@@ -983,19 +983,17 @@ 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)
@@ -1005,9 +1003,11 @@ 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();

}



/**
@@ -2245,6 +2245,7 @@ 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;
@@ -2282,6 +2283,7 @@ 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;

}
@@ -2292,6 +2294,7 @@ 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;
@@ -2306,6 +2309,7 @@ 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;

}
@@ -2344,6 +2348,7 @@ 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;
@@ -2369,6 +2374,7 @@ 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);
@@ -2499,6 +2505,7 @@ 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;
@@ -2506,6 +2513,7 @@ 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;

}
@@ -2711,6 +2719,7 @@ 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);
@@ -2763,6 +2772,7 @@ 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;

}
@@ -2781,6 +2791,7 @@ 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))
@@ -2801,6 +2812,7 @@ 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)

CRA Git | Maintained and supported by SUSTech CRA and CCSE