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    SubjectRe: [PATCH -mm 3/4][AIO] - AIO completion signal notification
    On Mon, 20 Nov 2006 15:22:52 +0100
    S__bastien Dugu__ <sebastien.dugue@bull.net> wrote:

    > +static long aio_setup_sigevent(struct aio_notify *notify,
    > + struct sigevent __user *user_event)
    > +{
    > + sigevent_t event;
    > + struct task_struct *target;
    > +
    > + if (copy_from_user(&event, user_event, sizeof (event)))
    > + return -EFAULT;
    > +
    > + if (event.sigev_notify == SIGEV_NONE)
    > + return 0;
    > +
    > + notify->notify = event.sigev_notify;
    > + notify->signo = event.sigev_signo;
    > + notify->value = event.sigev_value;
    > +
    > + read_lock(&tasklist_lock);
    > + target = good_sigevent(&event);
    > +
    > + if (unlikely(!target || (target->flags & PF_EXITING)))
    > + goto out_unlock;
    > +
    > + notify->target = target;
    > +
    > + if (notify->notify == (SIGEV_SIGNAL|SIGEV_THREAD_ID)) {
    > + /*
    > + * This reference will be dropped in really_put_req() when
    > + * we're done with the request.
    > + */
    > + get_task_struct(target);
    > + }

    It worries me that this function can save away a task_struct* without
    having taken a reference against it.


    > + read_unlock(&tasklist_lock);
    > +
    > + /*
    > + * NOTE: we cannot free the sigqueue in the completion path as
    > + * the signal may not have been delivered to the target task.
    > + * Therefore it has to be freed in __sigqueue_free() when the
    > + * signal is collected if si_code is SI_ASYNCIO.
    > + */
    > + notify->sigq = sigqueue_alloc();
    > +
    > + if (unlikely(!notify->sigq))
    > + return -EAGAIN;
    > +
    > + return 0;
    > +
    > +out_unlock:
    > + read_unlock(&tasklist_lock);
    > + return -EINVAL;
    > +}
    -
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