Re: [PATCH] cgroup: Properly init nr_tasks in cgroup_taskset

Tejun Heo
2017-09-15T15:47:52Z

Hello, Waiman.

On Thu, Sep 14, 2017 at 01:45:13PM -0700, Waiman Long wrote:
> Commit 610467270fb3 ("cgroup: don't call migration methods if there
> are no tasks to migrate") introduces a new field nr_tasks to the
> cgroup_taskset structure for keeping track of the number of tasks
> contained in the structure. The initial value of this field, however,
> is not guaranteed to be 0 as all the cgroup_taskset structures are
> allocated from stack. Therefore, we need to explicitly initilized
> it in the CGROUP_TASKSET_INIT() macro for the new code to behave
> correctly.
>
> Signed-off-by: Waiman Long <longman@redhat.com>
> ---
> kernel/cgroup/cgroup-internal.h | 1 +
> 1 file changed, 1 insertion(+)
>
> diff --git a/kernel/cgroup/cgroup-internal.h b/kernel/cgroup/cgroup-internal.h
> index 5151ff2..6b4c04e 100644
> --- a/kernel/cgroup/cgroup-internal.h
> +++ b/kernel/cgroup/cgroup-internal.h
> @@ -76,6 +76,7 @@ struct cgroup_mgctx {
> .src_csets = LIST_HEAD_INIT(tset.src_csets), \
> .dst_csets = LIST_HEAD_INIT(tset.dst_csets), \
> .csets = &tset.src_csets, \
> + .nr_tasks = 0, \

But it's an initialization macro, which means that the only way these
are used is as a part of whole struct initialization and the compiler
would always set the unspecified fields to zero.

Thanks.

--
tejun