Re: [PATCH i-g-t] tests/kms_explicit_fence: Rescue pending IN_FENCE waits on test failures

[Karthik B S <karthik.b.s@intel.com>]

Hi Pranay,

On 5/6/2026 10:08 AM, Samala, Pranay wrote:
> Hi Karthik,
>
>> -----Original Message-----
>> From: B S, Karthik <karthik.b.s@intel.com>
>> Sent: Monday, May 4, 2026 11:15 AM
>> To: igt-dev@lists.freedesktop.org
>> Cc: Samala, Pranay <pranay.samala@intel.com>; B S, Karthik
>> <karthik.b.s@intel.com>; Sebinraj, S <s.sebinraj@intel.com>; Karas, Krzysztof
>> <krzysztof.karas@intel.com>
>> Subject: [PATCH i-g-t] tests/kms_explicit_fence: Rescue pending IN_FENCE
>> waits on test failures
>>
>> Track per-plane timeline/fence state across the in-flight NONBLOCK atomic
>> commit and install an exit handler to signal any still-unsignaled fences.
>> This prevents cleanup hangs when an assertion fires after commit submission
>> but before the test signals the blocking fence.
>>
>> Cc: S Sebinraj <s.sebinraj@intel.com>
>> Cc: Krzysztof Karas <krzysztof.karas@intel.com>
>> Signed-off-by: Karthik B S <karthik.b.s@intel.com>
>> ---
>>   tests/kms_explicit_fence.c | 58
>> ++++++++++++++++++++++++++++++++++++++
>>   1 file changed, 58 insertions(+)
>>
>> diff --git a/tests/kms_explicit_fence.c b/tests/kms_explicit_fence.c index
>> 2ec9bf39d..7ffdcb285 100644
>> --- a/tests/kms_explicit_fence.c
>> +++ b/tests/kms_explicit_fence.c
>> @@ -68,6 +68,42 @@ typedef struct {
>>   	igt_pipe_crc_t *pipe_crc;
>>   } data_t;
>>
>> +/*
>> + * State tracked across the lifetime of an in-flight atomic commit that
>> +has
>> + * IN_FENCEs attached. The exit handler uses this to unblock any
>> +pending
>> + * commit if an assert hits between the commit and the point where
>> + * the test would otherwise signal the unsignaled fence(s).
>> + */
>> +static struct {
>> +	int timelines[NUM_PLANES];
>> +	bool needs_signal[NUM_PLANES];
>> +	bool active;
>> +} pending_fence_state = {
>> +	.timelines = { -1, -1, -1 },
>> +};
>> +
>> +static void signal_pending_fences(int sig) {
>> +	if (!pending_fence_state.active)
>> +		return;
>> +
>> +	for (int i = 0; i < NUM_PLANES; i++) {
>> +		if (pending_fence_state.timelines[i] < 0)
>> +			continue;
>> +
>> +		if (pending_fence_state.needs_signal[i]) {
>> +			/*
>> +			 * Best-effort: advance the timeline so the kernel
>> +			 * stops waiting on this IN_FENCE.
>> +			 */
>> +
>> 	sw_sync_timeline_inc(pending_fence_state.timelines[i], 1);
>> +			pending_fence_state.needs_signal[i] = false;
>> +		}
>> +	}
>> +
>> +	pending_fence_state.active = false;
>> +}
>> +
>>   static void setup_output(data_t *data)
>>   {
>>   	igt_display_t *display = &data->display; @@ -242,8 +278,14 @@
>> static void multiplane_atomic_fence_wait(data_t *data)
>>
>>   		/* Attach IN_FENCE_FD to plane */
>>   		igt_plane_set_fence_fd(planes[i], fences[i]);
>> +
>> +		pending_fence_state.timelines[i] = timelines[i];
>> +		pending_fence_state.needs_signal[i] = !should_signal[i];
>>   	}
>>
>> +	/* Arm the exit handler before the NONBLOCK commit goes out. */
>> +	pending_fence_state.active = true;
>> +
>>   	/* Swap overlay colors to detect scanout changes via CRC */
>>   	igt_plane_set_fb(data->overlay1, &data->overlay2_fb);
>>   	igt_plane_set_position(data->overlay1, OVERLAY1_POS_X,
>> OVERLAY1_POS_Y); @@ -299,6 +341,7 @@ static void
>> multiplane_atomic_fence_wait(data_t *data)
>>   	igt_assert_crc_equal(&crc_before, &crc_after);
>>
>>   	/* Now signal the blocking fence (overlay2) */
>> +	pending_fence_state.needs_signal[PLANE_OVERLAY2_IDX] = false;
>>   	sw_sync_timeline_inc(timelines[PLANE_OVERLAY2_IDX], 1);
>>
>>   	/* Wait for overlay2 fence to be signaled */ @@ -311,6 +354,12 @@
>> static void multiplane_atomic_fence_wait(data_t *data)
>>   	igt_assert_eq(ret, 0);
>>   	igt_assert_eq(sync_fence_status(out_fence), 1);
>>
>> +	/*
>> +	 * The pending atomic commit has now completed, so the exit
>> handler
>> +	 * no longer needs to rescue it.
>> +	 */
>> +	pending_fence_state.active = false;
>> +
> pending_fence_state.timelines[] retains stale fds after use. Consider resetting them to -1 in signal_pending_fences() after signaling, to avoid accidentally operating on a reused fd in edge cases.

Thank you for the review.

Agreed, will add this in v2.

Thanks and Regards,
Karthik.B.S
>
> Regards,
> Pranay
>
>>   	/* Verify display has now updated (CRC should differ from baseline)
>> */
>>   	igt_pipe_crc_get_current(data->drm_fd, data->pipe_crc, &crc_final);
>>
>> @@ -353,6 +402,13 @@ int igt_main()
>>
>>   		data.pipe_crc = igt_pipe_crc_new(data.drm_fd, data.crtc-
>>> crtc_index,
>> IGT_PIPE_CRC_SOURCE_AUTO);
>> +
>> +		/*
>> +		 * Make sure that on any failure mid-test, any unsignaled
>> +		 * IN_FENCE that the kernel is still waiting on gets
>> +		 * signaled so cleanup can complete instead of hanging.
>> +		 */
>> +		igt_install_exit_handler(signal_pending_fences);
>>   	}
>>
>>   	igt_describe("Test atomic commit with 3 planes (1 primary, 2 overlay)
>> "
>> @@ -363,6 +419,8 @@ int igt_main()
>>   		multiplane_atomic_fence_wait(&data);
>>
>>   	igt_fixture() {
>> +		signal_pending_fences(0);
>> +
>>   		reset_display_state(&data);
>>   		igt_pipe_crc_free(data.pipe_crc);
>>   		cleanup_crtc(&data);
>> --
>> 2.43.0