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sched/uclamp: Fix locking around cpu_util_update_eff()

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[ 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: 7226017ad3 ("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>
This commit is contained in:
Qais Yousef 2021-05-10 15:50:32 +01:00 committed by Greg Kroah-Hartman
parent 6c2b3d565f
commit 37481ad72d
1 changed files with 7 additions and 0 deletions
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7
kernel/sched/core.c
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@ -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;