Re: [PATCH] drm/i915/selftests: Fix error checking for wait_var_timeout

[Mika Kuoppala <mika.kuoppala@linux.intel.com>]

Chris Wilson <chris@chris-wilson.co.uk> writes:

> The old wait_on_atomic_t used a custom callback to perform the
> schedule(), which used my return semantics of reporting an error code on
> timeout. wait_var_event_timeout() uses the schedule() return semantics
> of reporting the remaining jiffies (1 if it timed out with 0 jiffies
> remaining!) and 0 on failure. This semantic mismatch lead to us falsely
> claiming a time out occurred.

I might have gone too far into the rabbit hole on this one.
The more I abseiled, the more there was macro trickery and
shadowing return values. Anxiety started to creep in.

I am back but will need to recuperate.

Reviewed-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>
>
> Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=106085
> Fixes: d224985a5e31 ("sched/wait, drivers/drm: Convert wait_on_atomic_t() usage to the new wait_var_event() API")
> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> ---
>  drivers/gpu/drm/i915/selftests/intel_breadcrumbs.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/selftests/intel_breadcrumbs.c b/drivers/gpu/drm/i915/selftests/intel_breadcrumbs.c
> index 46580026c7fc..d6926e7820e5 100644
> --- a/drivers/gpu/drm/i915/selftests/intel_breadcrumbs.c
> +++ b/drivers/gpu/drm/i915/selftests/intel_breadcrumbs.c
> @@ -412,10 +412,11 @@ static int igt_wakeup(void *arg)
>  		 * that they are ready for the next test. We wait until all
>  		 * threads are complete and waiting for us (i.e. not a seqno).
>  		 */
> -		err = wait_var_event_timeout(&done, !atomic_read(&done), 10 * HZ);
> -		if (err) {
> +		if (!wait_var_event_timeout(&done,
> +					    !atomic_read(&done), 10 * HZ)) {
>  			pr_err("Timed out waiting for %d remaining waiters\n",
>  			       atomic_read(&done));
> +			err = -ETIMEDOUT;
>  			break;
>  		}
>  
> -- 
> 2.17.0
>
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