Re: [3.6-rc7] switcheroo race with Intel HDA...

[Takashi Iwai]

At Fri, 12 Oct 2012 23:08:14 +0800,
Daniel J Blueman wrote:
> 
> On 10 October 2012 20:34, Takashi Iwai <tiwai@xxxxxxx> wrote:
> > At Tue, 9 Oct 2012 22:26:40 +0800,
> > Daniel J Blueman wrote:
> >> On 9 October 2012 21:04, Takashi Iwai <tiwai@xxxxxxx> wrote:
> >> > At Tue, 9 Oct 2012 19:23:56 +0800,
> >> > Daniel J Blueman wrote:
> >> >> On 9 October 2012 18:07, Takashi Iwai <tiwai@xxxxxxx> wrote:
> >> >> > At Tue, 09 Oct 2012 12:04:08 +0200,
> >> >> > Takashi Iwai wrote:
> >> >> >> At Tue, 9 Oct 2012 00:34:09 +0800,
> >> >> >> Daniel J Blueman wrote:
> >> >> >> > On 8 October 2012 20:58, Takashi Iwai <tiwai@xxxxxxx> wrote:
> >> >> >> > > At Tue, 25 Sep 2012 13:20:05 +0800,
> >> >> >> > > Daniel J Blueman wrote:
> >> >> >> > >> On my Macbook with a discrete Nvidia GPU, there is a race between
> >> >> >> > >> selecting the integrated GPU and putting the discrete GPU into D3 [1],
> >> >> >> > >> reliably causing a kernel oops [2].
> >> >> >> > >>
> >> >> >> > >> Introducing a delay of ~1s between the calls prevents this. When the
> >> >> >> > >> second 'OFF' write path executes, it looks like struct azx at
> >> >> >> > >> card->private_data hasn't yet been allocated yet [3], so there is
> >> >> >> > >> likely some locking missing.
> >> >> >> > >
> >> >> >> > > It's rather pci_get_drvdata() returning NULL (i.e. card is NULL, thus
> >> >> >> > > card->private_data causes Oops).  Could you check the patch like below
> >> >> >> > > and see whether you get a kernel warning (but no Oops) or the problem
> >> >> >> > > gets fixed by shifting the assignment of pci drvdata?
> >> >> >> > [...]
> >> >> >> >
> >> >> >> > Good patching. Calling pci_set_drvdata later prevents the oops in HDA,
> >> >> >> > though we see unexpected 0x0 responses in the response ring buffer
> >> >> >> > [1], which we don't see when there's a >~1.5s delay between IGD and
> >> >> >> > OFF.
> >> >> >>
> >> >> >> If the previous patch fixed, it means that the switching occurred
> >> >> >> during the device was being probed.  Maybe a better approach to
> >> >> >> register the VGA switcheroo after the proper initialization.
> >> >> >>
> >> >> >> The patch below is a revised one.  Please give it a try.
> >> >> >
> >> >> > Also, it's not clear which card spews the spurious response.
> >> >> > Apply the patch below in addition.
> >> >> [...]
> >> >>
> >> >> hda-intel: 0000:01:00.1: spurious response 0x0:0x0, last cmd=0x1f0004
> >> >> $ lspci -s :1:0.1
> >> >> 01:00.1 Audio device: NVIDIA Corporation Device 0e1b (rev ff)
> >> >>
> >> >> It's the NVIDIA device which presumably hasn't completed it's
> >> >> transition to D3 at the time the OFF is executed.
> >> >
> >> > OK, then could you try the patch below on the top of previous two
> >> > patches?
> >>
> >> The first IGD switcheroo command fails to switch to the integrated GPU:
> >>
> >> # cat /sys/kernel/debug/vgaswitcheroo/switch
> >> 0:DIS:+:Pwr:0000:01:00.0
> >> 1:IGD: :Pwr:0000:00:02.0
> >> 2:DIS-Audio: :Pwr:0000:01:00.1
> >> # echo IGD >/sys/kernel/debug/vgaswitcheroo/switch
> >> vga_switcheroo: client 1 refused switch
> >>
> >> I also instrumented snd_hda_lock_devices, but none of the failure
> >> paths are being taken, which would leave inconsistent state, as the
> >> return value isn't checked.
> >
> > Hm, right, the return value of snd_hda_lock_devices() isn't checked,
> > but I don't understand how this results like above.
> > Basically switching is protected by mutex in vga_switcheroo.c, so the
> > whole operation in the client side should be serialized.
> >
> > In anyway, try the patch below cleanly, and see the spurious message
> > error coming up at which timing.
> [...]
> 
> The patch _does_ address the issue. A recent update to my Macbook
> firmware misleadingly broke i915 switching, but since I can reproduce
> the oops without the IGD switching completing with the stock kernel,
> and consistently can't without [1], the patch is good.
> 
> Tested-by: Daniel J Blueman <daniel@xxxxxxxxx>

OK, then I'm going to apply the patch to 3.7 tree (with Cc to
stable).


thanks,

Takashi


> 
> Thanks Takashi!
>   Daniel
> 
> --- [1]
> 
> snd_hda_intel 0000:00:1b.0: enabling device (0000 -> 0002)
> snd_hda_intel 0000:00:1b.0: irq 54 for MSI/MSI-X
> XXX 0000:00:1b.0: azx_codec_create entered
> vga_switcheroo: enabled
> XXX 0000:00:1b.0: azx_codec_create done
> input: HDA Intel PCH Headphone as
> /devices/pci0000:00/0000:00:1b.0/sound/card0/input9
> snd_hda_intel 0000:01:00.1: enabling device (0000 -> 0002)
> hda_intel: Disabling MSI
> hda-intel: 0000:01:00.1: Handle VGA-switcheroo audio client
> XXX 0000:01:00.1: azx_codec_create entered
> XXX 0000:01:00.1: azx_codec_create done
> input: HDA NVidia HDMI/DP,pcm=8 as
> /devices/pci0000:00/0000:00:01.0/0000:01:00.1/sound/card1/input12
> input: HDA NVidia HDMI/DP,pcm=7 as
> /devices/pci0000:00/0000:00:01.0/0000:01:00.1/sound/card1/input13
> input: HDA NVidia HDMI/DP,pcm=3 as
> /devices/pci0000:00/0000:00:01.0/0000:01:00.1/sound/card1/input14
> vga_switcheroo: client 1 refused switch
> i915: switched off
> -- 
> Daniel J Blueman
> 
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