Hi,
Alan Stern <st...@rowland.harvard.edu> writes:
>> >> > On Thu, 29 Jun 2017, kernel test robot wrote:
>> >> >
>> >> >> FYI, we noticed the following commit:
>> >> >>
>> >> >> commit: f16443a034c7aa359ddf6f0f9bc40d01ca31faea ("USB: gadgetfs,
>> >> >> dummy-hcd, net2280: fix locking for callbacks")
>> >> >> https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git master
>> >> >>
>> >> >> in testcase: trinity
>> >> >> with following parameters:
>> >> >>
>> >> >> runtime: 300s
>> >> >>
>> >> >> test-description: Trinity is a linux system call fuzz tester.
>> >> >> test-url: http://codemonkey.org.uk/projects/trinity/
>> >> >>
>> >> >>
>> >> >> on test machine: qemu-system-x86_64 -enable-kvm -m 420M
>> >> >>
>> >> >> caused below changes (please refer to attached dmesg/kmsg for entire
>> >> >> log/backtrace):
>> >> > ...
>> >> >
>> >> > I won't include the entire report. The gist is that we have a problem
>> >> > with lock ordering. The report is about dummy-hcd, but this could
>> >> > affect any UDC driver.
>> >> >
>> >> > 1. When a SETUP request arrives, composite_setup() acquires
>> >> > cdev->lock before calling the function driver's callback.
>> >> > When that callback submits a reply, it causes the UDC driver
>> >> > to acquire its private lock.
>> >>
>> >> this only seems to happen before calling set_config():
>> >>
>> >> case USB_REQ_SET_CONFIGURATION:
>> >> if (ctrl->bRequestType != 0)
>> >> goto unknown;
>> >> if (gadget_is_otg(gadget)) {
>> >> if (gadget->a_hnp_support)
>> >> DBG(cdev, "HNP available\n");
>> >> else if (gadget->a_alt_hnp_support)
>> >> DBG(cdev, "HNP on another port\n");
>> >> else
>> >> VDBG(cdev, "HNP inactive\n");
>> >> }
>> >> spin_lock(&cdev->lock);
>> >> value = set_config(cdev, ctrl, w_value);
>> >> spin_unlock(&cdev->lock);
>> >> break;
>> >
>> > That's true. Why is the lock held for set_config() but not for any of
>> > the other callbacks?
>>
>> this is really old code from Dave. Your guess is as good as mine :-(
>>
>> > Doesn't that mean the other callbacks can race with function
>> > unregistration?
>>
>> Probably not as UDCs are required to cancel transfers and kill all
>> endpoints before unregistering. We would probably just giveback a few
>> requests with -ESHUTDOWN and prevent new ones from being queued to HW,
>> no?
>
> But SETUP callbacks aren't associated with pending requests. They get
they are if ->setup() returns DELAYED_STATUS.
> generated whenever a SETUP packet is received, even if the gadget
> driver has no requests queued. Cancelling transfers won't prevent
> them.
>
> Killing all endpoints might or might not do the trick. Does killing
> ep0 prevent the UDC driver from receiving SETUP packets? This may vary
> between UDC drivers.
no, it does not. If ->setup() fails, we are required to Stall and
restart ep0. Restarting ep0 involves preparing it to receive a new
SETUP request.
> There are also the other callbacks (reset, disconnect, bus suspend, and
> bus resume), which aren't associated with endpoints or requests at all.
>
> Probably drivers really should have something like synchronize_irq() in
> the udc_stop routine. That would solve a lot of problems (although it
> wouldn't help dummy_hcd, which doesn't rely on interrupts).
Hmm, free_irq() calls synchronize_irq(). UDCs should just request_irq()
on udc_start() and free_irq() on udc_stop(). That's what dwc3 is doing.
--
balbi
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