On Sun, 19 Aug 2012, Bruno Prémont wrote:
> > 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.
No, memory is not freed in usbhid_close(). It is freed in
usbhid_stop().
> 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
Right. Like I said, usbhid->outbuf is freed in hid_free_buffers(),
which is called from usbhid_stop().
Forget about usbhid_close(). The race is between hid_submit_out() and
usbhid_stop().
Alan Stern
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