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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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