Hello,
On Thu, Dec 22, 2011 at 02:26:55PM -0800, Mandeep Singh Baines wrote:
> @@ -2283,14 +2261,26 @@ static int attach_task_by_pid(struct cgroup *cgrp, u64 pid, bool threadgroup)
>
> threadgroup_lock(tsk);
>
> - if (threadgroup)
> + if (threadgroup) {
> + if (!thread_group_leader(tsk)) {
> + /*
> + * a race with de_thread from another thread's exec()
> + * may strip us of our leadership, if this happens,
> + * there is no choice but to throw this task away and
> + * try again (from cgroup_procs_write); this is
> + * "double-double-toil-and-trouble-check locking".
> + */
> + ret = -EAGAIN;
> + goto out_unlock_threadgroup;
> + }
> ret = cgroup_attach_proc(cgrp, tsk);
Ummm... can't we just do tsk = tsk->leader after locking threadgroup?
Why do we need to retry from the beginning?
Thanks.
--
tejun
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