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    SubjectRe: [PATCH][RFC] AIO: always reinitialize iocb->ki_run_list at the end of aio_run_iocb()
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    On Wednesday 26 May 2010 23:38:35 Jeff Moyer wrote:
    ...
    > I can vaguely recall discussion surrounding the reference counting of
    > cancel methods, but I have no idea what the actual contents of those
    > discussions were. Sorry, my memory has failed me. Either Zach or
    > Suparna might remember better.
    >
    > Sergey, the cancellation path, unfortunately, is not well exercised as
    > I'm sure you are aware. As you pointed out, the only implementation of
    > a cancel method is the usb gadget interface. Now, given that they've
    > worked fine with the extra put in their cancel method, I'm not sure why
    > you can't do the same.
    Well, in fact, they have only one aio_put_req() in their cancel method. This
    is the code from 2.6.34:

    static int ep_aio_cancel(struct kiocb *iocb, struct io_event *e)
    {
    struct kiocb_priv *priv = iocb->private;
    struct ep_data *epdata;
    int value;

    local_irq_disable();
    epdata = priv->epdata;
    // spin_lock(&epdata->dev->lock);
    kiocbSetCancelled(iocb);
    if (likely(epdata && epdata->ep && priv->req))
    value = usb_ep_dequeue (epdata->ep, priv->req);
    else
    value = -EINVAL;
    // spin_unlock(&epdata->dev->lock);
    local_irq_enable();

    aio_put_req(iocb);
    return value;
    }

    And adding extra aio_put_req() to the cancel method will not fix failing
    kick_iocb() which is another problem and this patch is supposed to address it.

    > I'd rather not muddy these waters even further. Unless there is a
    > compelling reason why the patch author cannot do an extra put in his
    > cancel method, I'd say that is the best way forward.
    >

    This patch is not about reference counting - it's about kick_iocb() failing
    due to NULL values of iocb->ki_run_list.next and iocb->ki_run_list.prev which
    are left after aio_run_iocb().

    > Cheers,
    > Jeff
    >

    --
    Regards, Sergey Temerkhanov,
    Cifronic ZAO


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