[PATCH v2 cgroup/for-3.11 1/3] cgroup: fix RCU accesses to task->cgroups
Li Zefan
lizefan at huawei.com
Wed Jun 26 03:28:38 UTC 2013
On 2013/6/26 2:48, Tejun Heo wrote:
> task->cgroups is a RCU pointer pointing to struct css_set. A task
> switches to a different css_set on cgroup migration but a css_set
> doesn't change once created and its pointers to cgroup_subsys_states
> aren't RCU protected.
>
> task_subsys_state[_check]() is the macro to acquire css given a task
> and subsys_id pair. It RCU-dereferences task->cgroups->subsys[] not
> task->cgroups, so the RCU pointer task->cgroups ends up being
> dereferenced without read_barrier_depends() after it. It's broken.
>
> Fix it by introducing task_css_set[_check]() which does
> RCU-dereference on task->cgroups. task_subsys_state[_check]() is
> reimplemented to directly dereference ->subsys[] of the css_set
> returned from task_css_set[_check]().
>
> This removes some of sparse RCU warnings in cgroup.
>
> v2: Fixed unbalanced parenthsis and there's no need to use
> rcu_dereference_raw() when !CONFIG_PROVE_RCU. Both spotted by Li.
>
> Signed-off-by: Tejun Heo <tj at kernel.org>
> Reported-by: Fengguang Wu <fengguang.wu at intel.com>
> Cc: stable at vger.kernel.org
Acked-by: Li Zefan <lizefan at huawei.com>
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