| From 781f1a70c27d436fcc93857ee3b8d5de8a761f5a Mon Sep 17 00:00:00 2001 |
| From: Sasha Levin <sashal@kernel.org> |
| Date: Mon, 10 May 2021 15:50:32 +0100 |
| Subject: sched/uclamp: Fix locking around cpu_util_update_eff() |
| |
| 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 c561c3b993b5..d4bbead59ad2 100644 |
| --- a/kernel/sched/core.c |
| +++ b/kernel/sched/core.c |
| @@ -7620,7 +7620,11 @@ 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; |
| @@ -7710,6 +7714,9 @@ 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; |
| -- |
| 2.30.2 |
| |
