On 09/14/2017 11:35 AM, Jens Axboe wrote:
> On 09/14/2017 11:28 AM, Srinath Mannam wrote:
>> Hi Bjorn,
>>
>> On Thu, Sep 14, 2017 at 10:52 PM, Jens Axboe <[email protected]> wrote:
>>>
>>> On 09/14/2017 11:11 AM, Bjorn Helgaas wrote:
>>>> [+cc linux-pci]
>>>>
>>>> On Thu, Sep 14, 2017 at 12:00 PM, Jens Axboe <[email protected]> wrote:
>>>>> On 09/12/2017 02:04 PM, Johannes Berg wrote:
>>>>>> On Tue, 2017-09-12 at 13:43 -0600, Jens Axboe wrote:
>>>>>>
>>>>>>> CC'ing the guilty part and Bjorn. I'm assuming it's the
>>>>>>> pci_is_enabled() check, since the rest of the patch shouldn't have
>>>>>>> functional changes.
>>>>>>
>>>>>> and pci_enable_bridge() already checks if it's already enabled, but
>>>>>> still enables mastering in that case if it isn't:
>>>>>>
>>>>>> static void pci_enable_bridge(struct pci_dev *dev)
>>>>>> {
>>>>>> [...]
>>>>>> if (pci_is_enabled(dev)) {
>>>>>> if (!dev->is_busmaster)
>>>>>> pci_set_master(dev);
>>>>>> return;
>>>>>> }
>>>>>>
>>>>>> so I guess due to the new check we end up with mastering disabled, and
>>>>>> thus the firmware can't load since that's a DMA thing?
>>>>>
>>>>> Bjorn/Srinath, any input here? This is a regression that prevents wifi
>>>>> from working on a pretty standard laptop. It'd suck to have this be in
>>>>> -rc1. Seems like the trivial fix would be:
>>>>>
>>>>>
>>>>> diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
>>>>> index b0002daa50f3..ffbe11dbdd61 100644
>>>>> --- a/drivers/pci/pci.c
>>>>> +++ b/drivers/pci/pci.c
>>>>> @@ -1394,7 +1394,7 @@ static int pci_enable_device_flags(struct pci_dev
>>>>> *dev, unsigned long flags)
>>>>> return 0; /* already enabled */
>>>>>
>>>>> bridge = pci_upstream_bridge(dev);
>>>>> - if (bridge && !pci_is_enabled(bridge))
>>>>> + if (bridge)
>> With this change and keeping "mutex_lock(&pci_bridge_mutex);" in
>> pci_enable_bridge functoin will causes a nexted lock.
>
> Took a look, and looks like you are right. That code looks like a mess,
> fwiw.
>
> I'd strongly suggest that the bad commit is reverted until a proper
> solution is found, since the simple one-liner could potentially
> introduce a deadlock with your patch applied.
BTW, your patch looks pretty bad too, introducing a random mutex
deep on code that can be recursive. Why isn't this check in
pci_enable_device_flags() enough to prevent double-enable of
an upstream bridge?
if (atomic_inc_return(&dev->enable_cnt) > 1)
return 0; /* already enabled */
--
Jens Axboe
