Re: [-mm] Add an owner to the mm_struct (v7)

[Paul Menage]

On Thu, Apr 3, 2008 at 11:11 AM, Balbir Singh <balbir@xxxxxxxxxxxxxxxxxx> wrote:
>  >
>  > Hmm, is this new check for delay_group_leader() safe? Won't we have
>  > called exit_cgroup() by this point, and hence be reassigned to the
>  > root cgroup? And so mm->owner->cgroups won't point to the right place?
>  >
>
>  cgroup_exit() comes in much later after exit_mm(). Moreover delay_group_leader()
>  is a function that checks to see if

Sorry, I was unclear.

Yes, the call to cgroup_exit() comes much later than exit_mm() - but
it probably does come before the other users of the mm have finished
using the mm. So can't we end up with a situation like this?

A (group leader) exits; at this point, A->mm->owner == A
A calls exit_mm(), sees delay_group_leader(), doesn't change A->mm->owner
A calls cgroup_exit(), A->cgroups is set to init_css_set.
B (another thread) does something with B->mm->owner->cgroups (e.g. VM
accounting) and accesses the wrong group

Paul
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