Re: [Intel-gfx] [PATCH v2] ALSA: hda/i915 - avoid hung task timeout in i915 wait

[Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>]

On 08/03/2022 17:27, Kai Vehmanen wrote:
> If kernel is built with hung task detection enabled and
> CONFIG_DEFAULT_HUNG_TASK_TIMEOUT set to less than 60 seconds,
> snd_hdac_i915_init() will trigger the hung task timeout in case i915 is
> not available and taint the kernel.
> 
> Split the 60sec wait into a loop of smaller waits to avoid this.
> 
> Reviewed-by: Lucas De Marchi <lucas.demarchi@intel.com>
> Co-developed-by: Ramalingam C <ramalingam.c@intel.com>
> Signed-off-by: Ramalingam C <ramalingam.c@intel.com>
> Signed-off-by: Kai Vehmanen <kai.vehmanen@linux.intel.com>
> ---
>   sound/hda/hdac_i915.c | 10 ++++++----
>   1 file changed, 6 insertions(+), 4 deletions(-)
> 
> Changes V1->V2:
>   - address local variable naming issue raised by Amadeusz
>     and use Takashi's proposal
> 
> diff --git a/sound/hda/hdac_i915.c b/sound/hda/hdac_i915.c
> index 454474ac5716..aa48bed7baf7 100644
> --- a/sound/hda/hdac_i915.c
> +++ b/sound/hda/hdac_i915.c
> @@ -143,7 +143,7 @@ static bool i915_gfx_present(void)
>   int snd_hdac_i915_init(struct hdac_bus *bus)
>   {
>   	struct drm_audio_component *acomp;
> -	int err;
> +	int err, i;
>   
>   	if (!i915_gfx_present())
>   		return -ENODEV;
> @@ -159,9 +159,11 @@ int snd_hdac_i915_init(struct hdac_bus *bus)
>   	if (!acomp->ops) {
>   		if (!IS_ENABLED(CONFIG_MODULES) ||
>   		    !request_module("i915")) {
> -			/* 60s timeout */

Where does this 60s come from and why is the fix to work around 
DEFAULT_HUNG_TASK_TIMEOUT in a hacky way deemed okay? For instance would 
limiting the wait here to whatever the kconfig is set to be an option?

Regards,

Tvrtko

> -			wait_for_completion_timeout(&acomp->master_bind_complete,
> -						    msecs_to_jiffies(60 * 1000));
> +			/* max 60s timeout */
> +			for (i = 0; i < 60; i++)
> +				if (wait_for_completion_timeout(&acomp->master_bind_complete,
> +								msecs_to_jiffies(1000)))
> +					break;
>   		}
>   	}
>   	if (!acomp->ops) {
> 
> base-commit: fd7698cf0858f8c5e659b655109cd93c2f15cdd3