[Intel-gfx] [PATCH] drm/i915: Wait for reset to complete before returning from debugfs/i915_wedged

[Tvrtko Ursulin]

On 10/03/2017 12:21, Chris Wilson wrote:
> Provide some serialisation between user operations by waiting for the
> reset initiated by setting i915_wedged to complete.
>
> Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> Cc: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
> Cc: Mika Kuoppala <mika.kuoppala at intel.com>
> ---
>  drivers/gpu/drm/i915/i915_debugfs.c | 4 ++++
>  1 file changed, 4 insertions(+)
>
> diff --git a/drivers/gpu/drm/i915/i915_debugfs.c b/drivers/gpu/drm/i915/i915_debugfs.c
> index 115433d46477..a1eccf2ef313 100644
> --- a/drivers/gpu/drm/i915/i915_debugfs.c
> +++ b/drivers/gpu/drm/i915/i915_debugfs.c
> @@ -4138,6 +4138,10 @@ i915_wedged_set(void *data, u64 val)
>  	i915_handle_error(dev_priv, val,
>  			  "Manually setting wedged to %llu", val);
>
> +	wait_on_bit(&dev_priv->gpu_error.flags,
> +		    I915_RESET_IN_PROGRESS,
> +		    TASK_UNINTERRUPTIBLE);
> +
>  	return 0;
>  }

I've spotted that the kerneldoc for wait_on_bit says "One uses 
wait_on_bit() where one is waiting for the bit to clear, but has no 
intention of setting it."

I assume this is to avoid races, which it seems this new wait also 
doesn't avoid. Should it grab struct mutex across wait and handle_error? 
Or if not possible what is the benefit of the patch, just something to 
help IGT? Could we instead have IGT wait on the reset in progress status 
itself by exporting the status? (If we don't already, haven't looked.)

Regards,

Tvrtko