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From: Luca Coelho <luca@coelho.fi>
To: Jens Axboe <axboe@kernel.dk>,
	Srinath Mannam <srinath.mannam@broadcom.com>
Cc: Bjorn Helgaas <bhelgaas@google.com>,
	Johannes Berg <johannes@sipsolutions.net>,
	"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>,
	Linus Torvalds <torvalds@linux-foundation.org>
Subject: Re: iwlwifi firmware load broken in current -git
Date: Fri, 15 Sep 2017 22:36:35 +0300
Message-ID: <1505504195.5400.295.camel@coelho.fi> (raw)
In-Reply-To: <ee04c95d-167b-0782-1860-253a2271d66c@kernel.dk>

On Fri, 2017-09-15 at 13:32 -0600, Jens Axboe wrote:
> On 09/14/2017 02:36 PM, Jens Axboe wrote:
> > 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.
> 
> Who's sending in the revert? I can certainly do it if no one else does,
> but it needs to be done.
> 
> I'm not seeing any patches coming out of Srinath to fix up the
> situation, so we should revert the broken patch until a better solution
> exists.

Bjorn already sent it:

https://lkml.org/lkml/2017/9/15/46

--
Cheers,
Luca.

  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
2017-09-15 19:32                         ` Jens Axboe
2017-09-15 19:36                           ` Luca Coelho [this message]
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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