Messages in this thread | | | Date | Fri, 03 Sep 2010 09:10:00 +0800 | From | Li Zefan <> | Subject | Re: [PATCH] cls_cgroup: Fix rcu lockdep warning |
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Peter Zijlstra wrote: > On Thu, 2010-09-02 at 14:30 +0800, Li Zefan wrote: >> Calling task_subsys_state() without holding rcu_read_lock or >> cgroup_mutex can cause lockdep warning. >> > > That is not a suitable changelog. > > Was the warning correct? Is your patch correct? What does RCU protect > here and why can we use classid after dropping it. > > Simply frobbing code to make the warning go away is not good. > >
task->cgroups and task->cgroups->subsys[i] are protected by RCU. So we avoid accessing invalid pointers here. This can happen, for example, when you are deref those pointers while someone move @task from one cgroup to another.
otoh, there is no lock rule for ->classid.
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