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    Subject[PATCH 5/7] Freezer: Fix kthread_create vs freezer theoretical race
    Date
    From: Oleg Nesterov <oleg@tv-sign.ru>

    kthread() sleeps in TASK_INTERRUPTIBLE state waiting for the first wakeup. In
    theory, this wakeup may come from freeze_process()->signal_wake_up(), so the
    task can disappear even before kthread_create() sets its ->comm.

    Change kthread() to use TASK_UNINTERRUPTIBLE.

    [akpm@linux-foundation.org: s/BUG_ON/WARN_ON+recover]

    Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>
    Acked-by: "Eric W. Biederman" <ebiederm@xmission.com>
    Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>
    ---
    kernel/kthread.c | 7 +++++--
    1 file changed, 5 insertions(+), 2 deletions(-)

    Index: linux-2.6/kernel/kthread.c
    ===================================================================
    --- linux-2.6.orig/kernel/kthread.c 2007-05-10 21:44:23.000000000 +0200
    +++ linux-2.6/kernel/kthread.c 2007-05-10 21:44:43.000000000 +0200
    @@ -70,7 +70,7 @@ static int kthread(void *_create)
    data = create->data;

    /* OK, tell user we're spawned, wait for stop or wakeup */
    - __set_current_state(TASK_INTERRUPTIBLE);
    + __set_current_state(TASK_UNINTERRUPTIBLE);
    complete(&create->started);
    schedule();

    @@ -162,7 +162,10 @@ EXPORT_SYMBOL(kthread_create);
    */
    void kthread_bind(struct task_struct *k, unsigned int cpu)
    {
    - BUG_ON(k->state != TASK_INTERRUPTIBLE);
    + if (k->state != TASK_UNINTERRUPTIBLE) {
    + WARN_ON(1);
    + return;
    + }
    /* Must have done schedule() in kthread() before we set_task_cpu */
    wait_task_inactive(k);
    set_task_cpu(k, cpu);
    -
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