[PATCH] drm/i915/gt: Disarm breadcrumbs if engines are already idle

[Janusz Krzysztofik]

From: Chris Wilson <chris at chris-wilson.co.uk>

The breadcrumbs use a GT wakeref for guarding the interrupt, but are
disarmed during release of the engine wakeref. This leaves a hole where
we may attach a breadcrumb just as the engine is parking (after it has
parked its breadcrumbs), execute the irq worker with some signalers still
attached, but never be woken again.

That issue manifests itself in CI with IGT runner timeouts while tests
are waiting indefinitely for release of all GT wakerefs.

<6> [209.151778] i915: Running live_engine_pm_selftests/live_engine_busy_stats
<7> [209.231628] i915 0000:00:02.0: [drm:intel_power_well_disable [i915]] disabling PW_5
<7> [209.231816] i915 0000:00:02.0: [drm:intel_power_well_disable [i915]] disabling PW_4
<7> [209.231944] i915 0000:00:02.0: [drm:intel_power_well_disable [i915]] disabling PW_3
<7> [209.232056] i915 0000:00:02.0: [drm:intel_power_well_disable [i915]] disabling PW_2
<7> [209.232166] i915 0000:00:02.0: [drm:intel_power_well_disable [i915]] disabling DC_off
<7> [209.232270] i915 0000:00:02.0: [drm:skl_enable_dc6 [i915]] Enabling DC6
<7> [209.232368] i915 0000:00:02.0: [drm:gen9_set_dc_state.part.0 [i915]] Setting DC state from 00 to 02
<4> [299.356116] [IGT] Inactivity timeout exceeded. Killing the current test with SIGQUIT.
...
<6> [299.356526] sysrq: Show State
...
<6> [299.373964] task:i915_selftest   state:D stack:11784 pid:5578  tgid:5578  ppid:873    flags:0x00004002
<6> [299.373967] Call Trace:
<6> [299.373968]  <TASK>
<6> [299.373970]  __schedule+0x3bb/0xda0
<6> [299.373974]  schedule+0x41/0x110
<6> [299.373976]  intel_wakeref_wait_for_idle+0x82/0x100 [i915]
<6> [299.374083]  ? __pfx_var_wake_function+0x10/0x10
<6> [299.374087]  live_engine_busy_stats+0x9b/0x500 [i915]
<6> [299.374173]  __i915_subtests+0xbe/0x240 [i915]
<6> [299.374277]  ? __pfx___intel_gt_live_setup+0x10/0x10 [i915]
<6> [299.374369]  ? __pfx___intel_gt_live_teardown+0x10/0x10 [i915]
<6> [299.374456]  intel_engine_live_selftests+0x1c/0x30 [i915]
<6> [299.374547]  __run_selftests+0xbb/0x190 [i915]
<6> [299.374635]  i915_live_selftests+0x4b/0x90 [i915]
<6> [299.374717]  i915_pci_probe+0x10d/0x210 [i915]

At the end of the interrupt worker, if there are no more engines awake,
disarm the breadcrumb and go to sleep.

Fixes: 9d5612ca165a ("drm/i915/gt: Defer enabling the breadcrumb interrupt to after submission")
Closes: https://gitlab.freedesktop.org/drm/intel/issues/10026
Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
Cc: Andrzej Hajda <andrzej.hajda at intel.com>
Cc: <stable at vger.kernel.org> # v5.12+
Signed-off-by: Janusz Krzysztofik <janusz.krzysztofik at linux.intel.com>
---
 drivers/gpu/drm/i915/gt/intel_breadcrumbs.c | 15 +++++++--------
 1 file changed, 7 insertions(+), 8 deletions(-)

diff --git a/drivers/gpu/drm/i915/gt/intel_breadcrumbs.c b/drivers/gpu/drm/i915/gt/intel_breadcrumbs.c
index d650beb8ed22f..20b9b04ec1e0b 100644
--- a/drivers/gpu/drm/i915/gt/intel_breadcrumbs.c
+++ b/drivers/gpu/drm/i915/gt/intel_breadcrumbs.c
@@ -263,8 +263,13 @@ static void signal_irq_work(struct irq_work *work)
 		i915_request_put(rq);
 	}
 
+	/* Lazy irq enabling after HW submission */
 	if (!READ_ONCE(b->irq_armed) && !list_empty(&b->signalers))
 		intel_breadcrumbs_arm_irq(b);
+
+	/* And confirm that we still want irqs enabled before we yield */
+	if (READ_ONCE(b->irq_armed) && !atomic_read(&b->active))
+		intel_breadcrumbs_disarm_irq(b);
 }
 
 struct intel_breadcrumbs *
@@ -315,13 +320,7 @@ void __intel_breadcrumbs_park(struct intel_breadcrumbs *b)
 		return;
 
 	/* Kick the work once more to drain the signalers, and disarm the irq */
-	irq_work_sync(&b->irq_work);
-	while (READ_ONCE(b->irq_armed) && !atomic_read(&b->active)) {
-		local_irq_disable();
-		signal_irq_work(&b->irq_work);
-		local_irq_enable();
-		cond_resched();
-	}
+	irq_work_queue(&b->irq_work);
 }
 
 void intel_breadcrumbs_free(struct kref *kref)
@@ -404,7 +403,7 @@ static void insert_breadcrumb(struct i915_request *rq)
 	 * the request as it may have completed and raised the interrupt as
 	 * we were attaching it into the lists.
 	 */
-	if (!b->irq_armed || __i915_request_is_complete(rq))
+	if (!READ_ONCE(b->irq_armed) || __i915_request_is_complete(rq))
 		irq_work_queue(&b->irq_work);
 }
 
-- 
2.44.0