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

[Takashi Iwai <tiwai@suse.de>]

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@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?


Takashi