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    SubjectRe: + cgroups-more-safe-tasklist-locking-in-cgroup_attach_proc.patch added to -mm tree
    Forgot to mention, sorry...

    That said, I believe the patch is correct and should fix the problem.

    On 09/02, Oleg Nesterov wrote:
    >
    > > From: Ben Blum <bblum@andrew.cmu.edu>
    > >
    > > Fix unstable tasklist locking in cgroup_attach_proc.
    > >
    > > According to this thread - https://lkml.org/lkml/2011/7/27/243 - RCU is
    > > not sufficient to guarantee the tasklist is stable w.r.t. de_thread and
    > > exit. Taking tasklist_lock for reading, instead of rcu_read_lock, ensures
    > > proper exclusion.
    >
    > I still think we should avoid the global lock.
    >
    > In any case, with tasklist or siglock,
    >
    > > - rcu_read_lock();
    > > + read_lock(&tasklist_lock);
    > > if (!thread_group_leader(leader)) {
    > > /*
    > > * a race with de_thread from another thread's exec() may strip
    > > @@ -2036,7 +2036,7 @@ int cgroup_attach_proc(struct cgroup *cg
    > > * throw this task away and try again (from cgroup_procs_write);
    > > * this is "double-double-toil-and-trouble-check locking".
    > > */
    > > - rcu_read_unlock();
    > > + read_unlock(&tasklist_lock);
    > > retval = -EAGAIN;
    >
    > this check+comment becomes completely pointless and imho very confusing.
    >
    > Oleg.



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