Paul Menage wrote: > On Fri, Nov 21, 2008 at 12:49 AM, Lai Jiangshan <laijs@xxxxxxxxxxxxxx> wrote: >> task_cgroup() calls cgroup_subsys_state(). > > No, it calls task_subsys_state() > >> and we must use rcu_read_lock() to protect cgroup_subsys_state(). >> so we must use rcu_read_lock() to protect task_cgroup(). >> >> but it'll not so friendly to caller: the callers of task_cgroup() have >> held cgroup_lock(). it means that struct cgroup will not be freed. >> >> So this patch add rcu_read_lock() in task_cgroup() to enhance task_cgroup(). >> And we do NOT NEED FIX task_cgroup()'s callers, and cgroup_lock() >> can protect task_cgroup(). > > Is there a reason to add an implicit rcu_read_lock() in task_cgroup() > and not directly in task_subsys_state() ? Yes. The caller have held the cgroup_lock() when it calls task_cgroup(). After we add an implicit rcu_read_lock() in task_cgroup(), we don't need rcu_read_lock()/task_lock() for using task_cgroup(). For cgroup_exit() will change tsk->cgroups, if we don't add an implicit rcu_read_lock() in task_cgroup(), we have to fix 7 places which using task_cgroup(). task_subsys_state() is different, it is used in fast path, If we add an implicit rcu_read_lock() in task_subsys_state(), we still need rcu_read_lock()/task_lock() for using it, so it's redundant rcu_read_lock(), and slower the fast path a little. Lai. > > Paul > _______________________________________________ Containers mailing list Containers@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linux-foundation.org/mailman/listinfo/containers
