Re: iwlwifi firmware load broken in current -git

[Srinath Mannam <srinath.mannam@broadcom.com>]

Hi Jens Axboe,


On Thu, Sep 14, 2017 at 11:14 PM, Jens Axboe <axboe@kernel.dk> wrote:
> 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 <axboe@kernel.dk> 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 <axboe@kernel.dk> 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 */
>
This check only to verify device enable not for the bus master check.
But device enable function calls the bridge enable if it has the bridge.
Bridge enable function enables both device and bus master.

Here the issue might be because, bridge of endpoint has already set
device enable without set bus master in some other context. which is
wrong.
because all bridges should enable with bridge_enable function only.
So we see the problem In this context, because "if (bridge &&
!pci_is_enabled(bridge))" check stops bridge enable which intern stops
bus master.
pci_enable_bridge function always makes sure that both device and bus
master are enabled in any case. If pci_enable_bridge function is not
called means, that bridge is already has device enable flag set. which
is not from pci_enable_bridge function.

Regards,
Srinath.

> --
> Jens Axboe
>