[Intel-gfx] [PATCH 4/4 V2] ALSA: hda - Continue probe in work context to avoid request_module deadlock

[Wang, Xingchao]

Hi Takashi,

> -----Original Message-----
> From: Takashi Iwai [mailto:tiwai at suse.de]
> Sent: Thursday, May 23, 2013 2:49 PM
> To: Wang Xingchao
> Cc: alsa-devel at alsa-project.org; intel-gfx at lists.freedesktop.org;
> david.henningsson at canonical.com; Girdwood, Liam R; Li, Jocelyn; Wang,
> Xingchao; Lin, Mengdong
> Subject: Re: [PATCH 4/4 V2] ALSA: hda - Continue probe in work context to avoid
> request_module deadlock
> 
> At Thu, 23 May 2013 09:51:07 +0800,
> Wang Xingchao wrote:
> >
> > There's deadlock when request_module(i915) in azx_probe.
> > It looks like:
> > device_lock(audio pci device) -> azx_probe -> module_request (or
> > symbol_request) -> modprobe (userspace) -> i915 init -> drm_pci_init
> > -> pci_register_driver -> bus_add_driver -> driver_attach -> which in
> > turn tries all locks on pci bus, and when it tries the one on the
> > audio device, it will deadlock.
> >
> > This patch introduce a work to store remaining probe stuff, and let
> > request_module run in safe work context.
> >
> > Signed-off-by: Wang Xingchao <xingchao.wang at linux.intel.com>
> > ---
> >  sound/pci/hda/hda_i915.c  |  13 ++++--  sound/pci/hda/hda_intel.c |
> > 105 +++++++++++++++++++++++++++-------------------
> >  2 files changed, 71 insertions(+), 47 deletions(-)
> >
> > diff --git a/sound/pci/hda/hda_i915.c b/sound/pci/hda/hda_i915.c index
> > 76c13d5..7547b20 100644
> > --- a/sound/pci/hda/hda_i915.c
> > +++ b/sound/pci/hda/hda_i915.c
> > @@ -42,13 +42,18 @@ int hda_i915_init(void)  {
> >  	int err = 0;
> >
> > -	get_power = symbol_request(i915_request_power_well);
> > +	get_power = symbol_get(i915_request_power_well);
> >  	if (!get_power) {
> > -		snd_printk(KERN_WARNING "hda-i915: get_power symbol get
> fail\n");
> > -		return -ENODEV;
> > +		request_module("i915");
> > +		get_power = symbol_get(i915_request_power_well);
> > +		if (!get_power) {
> > +			snd_printk(KERN_WARNING "hda-i915: get_power symbol get
> fail\n");
> > +			return -ENODEV;
> > +		}
> > +		snd_printdd("hda-i915: get_power symbol get successful\n");
> 
> Why do you need this change?
> 

symbol_request() should be the better API in such case but in my test it doesnot really load i915 module, that's why
I call request_module(i915) directly here.

Please note there's parameter difference:
request_module("i915")
symbol_request(i915_reauest_power_well)-->request_module("symbol:i915_request_power_well")

I donot know why the second one did not really load the module.

Thanks
--xingchao