Messages in this thread | | | Date | Thu, 22 Dec 2011 14:51:02 -0800 | From | Tejun Heo <> | Subject | Re: [PATCH 1/2] cgroup: remove tasklist_lock from cgroup_attach_proc |
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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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