Messages in this thread | | | Date | Fri, 2 Sep 2011 17:55:34 +0200 | From | Oleg Nesterov <> | Subject | Re: + cgroups-more-safe-tasklist-locking-in-cgroup_attach_proc.patch added to -mm tree |
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On 09/02, Ben Blum wrote: > > On Fri, Sep 02, 2011 at 04:00:15PM +0200, Oleg Nesterov wrote: > > Forgot to mention, sorry... > > > > That said, I believe the patch is correct and should fix the problem. > > Thanks! > > But I don't think the check becomes pointless? If a sub-thread execs > right before read_lock(&tasklist_lock) (but after the find_task_by_vpid > in attach_task_by_pid), that causes the case that the comment refers to.
How so? The comment says:
* a race with de_thread from another thread's exec() may strip * us of our leadership, making while_each_thread unsafe
This is not true.
And. Given that ->group_leader can be changed right after we drop tasklist this check is pointless. Yes, it can detect the case when this task_struct has nothing to do with this process sometimes, but not in general. (This connects to other problems I mentioned).
IOW, personally I think it would be better to update the patch. But I won't insist.
Oleg.
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