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    Subject[186/272] sched, cgroup: Use exit hook to avoid use-after-free crash
    2.6.37-stable review patch.  If anyone has any objections, please let us know.

    ------------------

    From: Peter Zijlstra <peterz@infradead.org>

    commit 068c5cc5ac7414a8e9eb7856b4bf3cc4d4744267 upstream.

    By not notifying the controller of the on-exit move back to
    init_css_set, we fail to move the task out of the previous
    cgroup's cfs_rq. This leads to an opportunity for a
    cgroup-destroy to come in and free the cgroup (there are no
    active tasks left in it after all) to which the not-quite dead
    task is still enqueued.

    Reported-by: Miklos Vajna <vmiklos@frugalware.org>
    Fixed-by: Mike Galbraith <efault@gmx.de>
    Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
    Cc: Mike Galbraith <efault@gmx.de>
    Signed-off-by: Ingo Molnar <mingo@elte.hu>
    LKML-Reference: <1293206353.29444.205.camel@laptop>
    Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

    ---
    kernel/sched.c | 18 ++++++++++++++++++
    1 file changed, 18 insertions(+)

    --- a/kernel/sched.c
    +++ b/kernel/sched.c
    @@ -607,6 +607,9 @@ static inline struct task_group *task_gr
    {
    struct cgroup_subsys_state *css;

    + if (p->flags & PF_EXITING)
    + return &root_task_group;
    +
    css = task_subsys_state_check(p, cpu_cgroup_subsys_id,
    lockdep_is_held(&task_rq(p)->lock));
    return container_of(css, struct task_group, css);
    @@ -9178,6 +9181,20 @@ cpu_cgroup_attach(struct cgroup_subsys *
    }
    }

    +static void
    +cpu_cgroup_exit(struct cgroup_subsys *ss, struct task_struct *task)
    +{
    + /*
    + * cgroup_exit() is called in the copy_process() failure path.
    + * Ignore this case since the task hasn't ran yet, this avoids
    + * trying to poke a half freed task state from generic code.
    + */
    + if (!(task->flags & PF_EXITING))
    + return;
    +
    + sched_move_task(task);
    +}
    +
    #ifdef CONFIG_FAIR_GROUP_SCHED
    static int cpu_shares_write_u64(struct cgroup *cgrp, struct cftype *cftype,
    u64 shareval)
    @@ -9250,6 +9267,7 @@ struct cgroup_subsys cpu_cgroup_subsys =
    .destroy = cpu_cgroup_destroy,
    .can_attach = cpu_cgroup_can_attach,
    .attach = cpu_cgroup_attach,
    + .exit = cpu_cgroup_exit,
    .populate = cpu_cgroup_populate,
    .subsys_id = cpu_cgroup_subsys_id,
    .early_init = 1,



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