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SubjectRe: [PATCH -mm 3/3][AIO] - AIO completion signal notification
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On Thu, 2006-11-09 at 19:08 +0000, Christoph Hellwig wrote:
> > +static long aio_setup_sigevent(struct kiocb *iocb,
> > + struct sigevent __user *user_event)
> > +{
> > + int error = 0;
> > + sigevent_t event;
> > + struct task_struct *target;
> > + unsigned long flags;
> > +
> > + if (!access_ok(VERIFY_READ, user_event, sizeof(struct sigevent)))
> > + return -EFAULT;
> > +
> > + if (copy_from_user(&event, user_event, sizeof (event)))
> > + return -EFAULT;
> > +
>
> > +
> > + /* Check for the SIGEV_NONE case */
> > + if (event.sigev_notify == SIGEV_NONE)
> > + return 0;
> > +
> > + /* Setup the request completion notification parameters */
> > + iocb->ki_notify.notify = event.sigev_notify;
> > + iocb->ki_notify.signo = event.sigev_signo;
> > + iocb->ki_notify.value = event.sigev_value;
> > +
> > + /* Now get the notification target */
> > + read_lock(&tasklist_lock);
> > +
> > + if ((target = good_sigevent(&event))) {
> > +
> > + spin_lock_irqsave(&target->sighand->siglock, flags);
> > +
> > + if (!(target->flags & PF_EXITING)) {
> > + iocb->ki_notify.target = target;
> > +
> > + spin_unlock_irqrestore(&target->sighand->siglock, flags);
> > +
>
> I don't think there's a need to have the siglock for checking PF_EXITING,
> and I also don't see why you need it for the assignment to
> iocb->ki_notify.target. What is it intended to protect?

Right, some remnant that managed to sneak through, will fix.

>
> > + /*
> > + * Get a ref on the task. It is dropped in really_put_req()
> > + * when we're done with the iocb, be it from the normal
> > + * completion path, the cancellation path or an error path.
> > + */
> > + if (iocb->ki_notify.notify == (SIGEV_SIGNAL|SIGEV_THREAD_ID))
> > + get_task_struct(target);
> > + } else {
> > + spin_unlock_irqrestore(&target->sighand->siglock, flags);
> > + error = -EINVAL;
> > + }
> > + } else
> > + error = -EINVAL;
> > +
> > + read_unlock(&tasklist_lock);
> > +
> > + if (!error) {
> > + /*
> > + * Alloc a sigqueue for this request
> > + *
> > + * 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.
> > + */
> > + if (unlikely(!(iocb->ki_sigq = sigqueue_alloc())))
> > + error = -EAGAIN;
>
> We leak the task reference here.

I don't think so, the reference is dropped in really_pu_req() when
the iocb is freed, unless I missed something.

>
> All in all aio_setup_sigevent is a big mess and the style is very odd.
> It's also overcommented on what's beeing done instead of why.
> I've attached an draft on how it should look like below.
>
> > + /* handle setting up the sigevent for POSIX AIO signals */
> > + req->ki_notify.notify = SIGEV_NONE;
> > +
> > + if (iocb->aio_sigeventp) {
> > + ret = aio_setup_sigevent(req,
> > + (struct sigevent __user *)(unsigned long)
> > + iocb->aio_sigeventp);
> > + if (ret)
> > + goto out_put_req;
> > + }
> > +
> > ret = aio_setup_iocb(req);
> >
> > if (ret)
> > @@ -1610,6 +1729,10 @@ int fastcall io_submit_one(struct kioctx
> > return 0;
> >
> > out_put_req:
> > + /* Undo the sigqueue alloc if someting went bad */
> > + if (req->ki_sigq)
> > + sigqueue_free(req->ki_sigq);
> > +
>
> Please put this after a separate label, so only callers after
> aio_setup_sigevent try to check ki_sigq.


Okay, cleaner that way.
>
>
>
> static long aio_setup_sigevent(struct kiocb *iocb,
> struct sigevent __user *user_event)
> {
> sigevent_t event;
> struct task_struct *target;
> unsigned long flags;
>
> if (copy_from_user(&event, user_event, sizeof (event)))
> return -EFAULT;
>
> if (event.sigev_notify == SIGEV_NONE)
> return 0;
>
> iocb->ki_notify.notify = event.sigev_notify;
> iocb->ki_notify.signo = event.sigev_signo;
> iocb->ki_notify.value = event.sigev_value;
>
> read_lock(&tasklist_lock);
> target = good_sigevent(&event);
> if (unlikely(!target || (target->flags & PF_EXITING)))
> goto out_unlock;
> iocb->ki_notify.target = target;
>
> if (iocb->ki_notify.notify == (SIGEV_SIGNAL|SIGEV_THREAD_ID)) {
> /*
> * This reference will be dropped when we're done with
> * the request.
> */
> get_task_struct(target);
> }
> 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.
> */
> iocb->ki_sigq = sigqueue_alloc();
> if (unlikely(!iocb->ki_sigq)) {
> put_task_struct(target);
> return -EAGAIN;
> }
>
> return 0;
> out_unlock:
> read_unlock(&tasklist_lock);
> return -EINVAL;
> }
>

Cool, clearly better without taking the siglock, but again I don't
think the put_task_struct() is needed here.

Thanks,

Sébastien.


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