Messages in this thread | | | Date | Wed, 16 Apr 2008 21:17:34 -0700 | From | "Paul Menage" <> | Subject | Re: [PATCH] cgroup: fix a race condition in manipulating tsk->cg_list |
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On Wed, Apr 16, 2008 at 9:11 PM, Andrew Morton <akpm@linux-foundation.org> wrote: > > I don't fully understand the race. Both paths hold css_set_lock. > > Can you describe it in more detail please?
Task A starts exiting, passes the check for unlinking current->cg_list.
Before it completely exits task B does the very first cgroup_iter_begin() call (via reading a cgroups tasks file) which links all tasks in to their css_set objects via tsk->cg_list.
Then task A finishes exiting and is freed, but doesn't unlink from the cg_list.
> > afacit the task at *p could set PF_EXITING immediately after this code has > tested PF_EXITING and then the task at *p could proceed until we hit the > same race (whatever that is).
The important fact there is that the task sets PF_EXITING *before* it checks whether it needs to unlink from current->cg_list.
Paul
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