[Intel-gfx] [PATCH] drm/i915: Handle full s64 precision for wait-ioctl

[Joonas Lahtinen]

On la, 2017-08-05 at 20:19 +0100, Chris Wilson wrote:
> The wait-ioctl is optionally supplied a timeout with nanosecond
> precision in a s64 field. We use nsecs_to_jiffies64() to convert that
> into the jiffies consumed by the scheduler, but internally
> nsecs_to_jiffies64() does not guard against overflow (as it's purpose is
> for use by the scheduler and not drivers!). So we must guard against the
> overflow ourselves, and in the process note that we may then return
> much earlier than the timeout selected by the user, so don't report
> ETIME unless we do hit the timeout. (Woe betold us though if the user
> waits for a year (32bit) and the request is still not complete!)
> 
> Reported-by: Jason Ekstrand <jason.ekstrand at intel.com>
> Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> Cc: Joonas Lahtinen <joonas.lahtinen at linux.intel.com>
> Cc: Daniel Vetter <daniel.vetter at ffwll.ch>

<SNIP>

> diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
> index 44df7dc3f880..b5794add4a3a 100644
> --- a/drivers/gpu/drm/i915/i915_gem.c
> +++ b/drivers/gpu/drm/i915/i915_gem.c
> @@ -3543,6 +3543,10 @@ i915_gem_wait_ioctl(struct file *filp,
>  		 */
>  		if (ret == -ETIME && !nsecs_to_jiffies(arg.timeout_ns))
>  			arg.timeout_ns = 0;
> +
> +		/* Asked to wait beyond the jiffie/scheduler precision */
> +		if (ret == -ETIME && arg.timeout_ns)
> +			ret = -EAGAIN;

-EAGAIN is documented as "GPU wedged" in the ioctl documentation. So
better update that documentation.

Regards, Joonas
-- 
Joonas Lahtinen
Open Source Technology Center
Intel Corporation