Commit 93b73858 authored by Qais Yousef's avatar Qais Yousef Committed by Peter Zijlstra
Browse files

sched/uclamp: Fix locking around cpu_util_update_eff() 



cpu_cgroup_css_online() calls cpu_util_update_eff() without holding the
uclamp_mutex or rcu_read_lock() like other call sites, which is
a mistake.

The uclamp_mutex is required to protect against concurrent reads and
writes that could update the cgroup hierarchy.

The rcu_read_lock() is required to traverse the cgroup data structures
in cpu_util_update_eff().

Surround the caller with the required locks and add some asserts to
better document the dependency in cpu_util_update_eff().

Fixes: 7226017a ("sched/uclamp: Fix a bug in propagating uclamp value in new cgroups")
Reported-by: default avatarQuentin Perret <qperret@google.com>
Signed-off-by: default avatarQais Yousef <qais.yousef@arm.com>
Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20210510145032.1934078-3-qais.yousef@arm.com
parent 0c18f2ec

kernel/sched/core.c

+7 −0
Original line number Diff line number Diff line
@@ -9507,7 +9507,11 @@ static int cpu_cgroup_css_online(struct cgroup_subsys_state *css) 


#ifdef CONFIG_UCLAMP_TASK_GROUP

	/* Propagate the effective uclamp value for the new group */

	mutex_lock(&uclamp_mutex);

	rcu_read_lock();

	cpu_util_update_eff(css);

	rcu_read_unlock();

	mutex_unlock(&uclamp_mutex);

#endif



	return 0;
@@ -9597,6 +9601,9 @@ static void cpu_util_update_eff(struct cgroup_subsys_state *css) 
	enum uclamp_id clamp_id;

	unsigned int clamps;



	lockdep_assert_held(&uclamp_mutex);

	SCHED_WARN_ON(!rcu_read_lock_held());



	css_for_each_descendant_pre(css, top_css) {

		uc_parent = css_tg(css)->parent

			? css_tg(css)->parent->uclamp : NULL;