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> > > > > + percpu_down_write(&scx_cgroup_ops_rwsem); > > > > > + cgroup_lock(); > > > > > } > > > > > > > > Shouldn't we acquire cgroup_lock() before scx_cgroup_ops_rwsem to avoid > > > > a potential AB-BA deadlock? > > > > > > There's no existing ordering between the two locks, so any order should be > > > safe. The reason why I put it in this particular order is because any > > > cgroup_lock() holder has no reason to grab ops_rwsem now or in the future > > > while the opposite direction is still unlikely but theoretically more > > > possible. > > > > Isn't scx_group_set_weight() called with cgroup_mutex held? In this case > > the order is cgroup_lock() -> scx_cgroup_ops_rwsem, or am I missing > > something? > > Oh, no, cgroup_lock() is only held for operations that change the cgroup > hierarchy - cgroup creation, deletion, controller enable/disable, task > migration and so on. Writes to control knobs doesn't acquire cgroup_lock(). Ah! That's the part I was missing, thanks for clarifying it. In that case: Acked-by: Andrea Righi -Andrea