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    SubjectRe: INFO: suspicious rcu_dereference_check() usage - include/linux/cgroup.h:492 invoked rcu_dereference_check() without protection!
    Should be [tip:core/urgent]

    Acked-by: Lai Jiangshan <laijs@cn.fujitsu.com>

    Paul E. McKenney wrote:
    >
    > Looks reasonable to me!
    >
    > Acked-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
    >
    >> Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
    >> ---
    >> kernel/sched.c | 10 ++++++++++
    >> 1 files changed, 10 insertions(+), 0 deletions(-)
    >>
    >> diff --git a/kernel/sched.c b/kernel/sched.c
    >> index 3acf694..2e06d87 100644
    >> --- a/kernel/sched.c
    >> +++ b/kernel/sched.c
    >> @@ -323,6 +323,15 @@ static inline struct task_group *task_group(struct task_struct *p)
    >> /* Change a task's cfs_rq and parent entity if it moves across CPUs/groups */
    >> static inline void set_task_rq(struct task_struct *p, unsigned int cpu)
    >> {
    >> + /*
    >> + * Strictly speaking this rcu_read_lock() is not needed since the
    >> + * task_group is tied to the cgroup, which in turn can never go away
    >> + * as long as there are tasks attached to it.
    >> + *
    >> + * However since task_group() uses task_subsys_state() which is an
    >> + * rcu_dereference() user, this quiets CONFIG_PROVE_RCU.
    >> + */
    >> + rcu_read_lock();
    >> #ifdef CONFIG_FAIR_GROUP_SCHED
    >> p->se.cfs_rq = task_group(p)->cfs_rq[cpu];
    >> p->se.parent = task_group(p)->se[cpu];
    >> @@ -332,6 +341,7 @@ static inline void set_task_rq(struct task_struct *p, unsigned int cpu)
    >> p->rt.rt_rq = task_group(p)->rt_rq[cpu];
    >> p->rt.parent = task_group(p)->rt_se[cpu];
    >> #endif
    >> + rcu_read_unlock();
    >> }
    >>
    >> #else
    >>
    >>
    > --
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