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From: Jens Axboe <axboe@kernel.dk>
To: Srinath Mannam <srinath.mannam@broadcom.com>
Cc: Bjorn Helgaas <bhelgaas@google.com>,
	Johannes Berg <johannes@sipsolutions.net>,
	Luca Coelho <luca@coelho.fi>,
	"Grumbach, Emmanuel" <emmanuel.grumbach@intel.com>,
	linuxwifi <linuxwifi@intel.com>,
	"linux-wireless@vger.kernel.org" <linux-wireless@vger.kernel.org>,
	"linux-pci@vger.kernel.org" <linux-pci@vger.kernel.org>
Subject: Re: iwlwifi firmware load broken in current -git
Date: Thu, 14 Sep 2017 14:36:06 -0600
Message-ID: <a5fd0c11-916f-1404-c979-2fd566ed72ec@kernel.dk> (raw)
In-Reply-To: <CABe79T79WhBh66iQB-5LLCQO0d37evg5tsKUGkj7+z8vNGTHcA@mail.gmail.com>

On 09/14/2017 02:04 PM, Srinath Mannam wrote:
> 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.

In any case, your patch introduces a regression on systems. Please get
it reverted now, and then you can come up with a new approach to fix the
double enable of the upstream bridge.

-- 
Jens Axboe

  reply index

Thread overview: 31+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-09-12 15:48 Jens Axboe
2017-09-12 16:11 ` Coelho, Luciano
2017-09-12 16:35   ` Jens Axboe
2017-09-12 16:36   ` Luca Coelho
2017-09-12 16:59     ` Jens Axboe
2017-09-12 19:43     ` Jens Axboe
2017-09-12 19:51       ` Luca Coelho
2017-09-12 20:04       ` Johannes Berg
2017-09-14 17:00         ` Jens Axboe
2017-09-14 17:11           ` Bjorn Helgaas
2017-09-14 17:22             ` Jens Axboe
2017-09-14 17:28               ` Srinath Mannam
2017-09-14 17:35                 ` Jens Axboe
2017-09-14 17:44                   ` Srinath Mannam
2017-09-14 17:45                     ` Jens Axboe
2017-09-14 17:50                     ` Johannes Berg
2017-09-14 17:44                   ` Jens Axboe
2017-09-14 20:04                     ` Srinath Mannam
2017-09-14 20:36                       ` Jens Axboe [this message]
2017-09-15 19:32                         ` Jens Axboe
2017-09-15 19:36                           ` Luca Coelho
2017-09-15 19:46                             ` Jens Axboe
2017-09-15 19:38                           ` Linus Torvalds
2017-09-15 19:43                             ` Luca Coelho
2017-09-15 19:51                               ` Linus Torvalds
2017-09-15 19:57                                 ` Jens Axboe
2017-09-15 19:48                             ` Jens Axboe
2017-09-15 19:51                               ` Luca Coelho
2017-09-15 19:55                                 ` Jens Axboe
2017-09-16  3:03                                   ` Bjorn Helgaas
2017-09-16 18:53                                     ` Jens Axboe

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