From: Qais Yousef qais.yousef@arm.com
[ Upstream commit 93b73858701fd01de26a4a874eb95f9b7156fd4b ]
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: 7226017ad37a ("sched/uclamp: Fix a bug in propagating uclamp value in new cgroups") Reported-by: Quentin Perret qperret@google.com Signed-off-by: Qais Yousef qais.yousef@arm.com Signed-off-by: Peter Zijlstra (Intel) peterz@infradead.org Link: https://lkml.kernel.org/r/20210510145032.1934078-3-qais.yousef@arm.com Signed-off-by: Sasha Levin sashal@kernel.org --- kernel/sched/core.c | 7 +++++++ 1 file changed, 7 insertions(+)
diff --git a/kernel/sched/core.c b/kernel/sched/core.c index 49b713da023d..94002cb551c4 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -8702,7 +8702,11 @@ 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; @@ -8792,6 +8796,9 @@ 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;