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    SubjectRe: [PATCH 0/7] HID: picoLCD updates
    On Sat, 18 August 2012 Alan Stern wrote:
    > On Sat, 18 Aug 2012, Bruno Prémont wrote:
    >
    > > One thing I just though about, how does usbhid handle the calls to
    > > usbhid_submit_report() when hid_hw_stop()/hid_hw_close() have already
    > > been called?
    >
    > Looks like they aren't synchronized at all. That's a bug.
    > usbhid_submit_report() should check the HID_DISCONNECTED flag.
    >
    > > I will attempt to see if it makes a difference to shortcut my
    > > usbhid_submit_report() calls from the point on I have called hid_hw_close()...
    >
    > I don't know bout hid_hw_close(). Certainly no more reports should be
    > submitted following usbhid_stop().

    Ok, I did just that, prevent new calls to usbhid_submit_report(), after
    calling hid_hw_close(), fixed one bug in my code that triggers the NULL
    pointer dereference (calling hid_set_drvdata(hdev, NULL) too early).

    Now I'm still seeing the bad paging request in _mmx_memcpy(), though rather
    sporadically.
    The last ones I saw were during remove() around the time of calling hid_hw_close()
    and hid_hw_stop(). Adding a printk() between the two (at least while picoLCD
    is hosting fbcon) makes it very improbably for the bad page to happen.

    It looks like low-level driver did free memory in hid_hw_close() for some
    in-flight URB and thus things break in following USB interrupt.

    From mapping trace information to source it seems:
    usbhid/hid-core.c:
    static int hid_submit_out(struct hid_device *hid)
    {
    struct hid_report *report;
    char *raw_report;
    struct usbhid_device *usbhid = hid->driver_data;
    int r;

    report = usbhid->out[usbhid->outtail].report;
    raw_report = usbhid->out[usbhid->outtail].raw_report;

    usbhid->urbout->transfer_buffer_length = ((report->size - 1) >> 3) +
    1 + (report->id > 0);
    usbhid->urbout->dev = hid_to_usb_dev(hid);
    if (raw_report) {
    memcpy(usbhid->outbuf, raw_report,
    usbhid->urbout->transfer_buffer_length);
    ^^^^^^^^^^^^^^^_ this is exploding
    kfree(raw_report);
    usbhid->out[usbhid->outtail].raw_report = NULL;
    }

    dbg_hid("submitting out urb\n");

    r = usb_submit_urb(usbhid->urbout, GFP_ATOMIC);
    if (r < 0) {
    hid_err(hid, "usb_submit_urb(out) failed: %d\n", r);
    return r;
    }
    usbhid->last_out = jiffies;
    return 0;
    }


    Bruno
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