[PATCH] drm/i915: fix blank screen booting crashes

[Matthew Brost <matthew.brost@xxxxxxxxx>]

From: Hugh Dickins <hughd@xxxxxxxxxx>

5.15-rc1 crashes with blank screen when booting up on two ThinkPads
using i915.  Bisections converge convincingly, but arrive at different
and surprising "culprits", none of them the actual culprit.

netconsole (with init_netconsole() hacked to call i915_init() when
logging has started, instead of by module_init()) tells the story:

kernel BUG at drivers/gpu/drm/i915/i915_sw_fence.c:245!
with RSI: ffffffff814d408b pointing to sw_fence_dummy_notify().
I've been building with CONFIG_CC_OPTIMIZE_FOR_SIZE=y, and that
function needs to be 4-byte aligned.

v2:
 (Jani Nikula)
  - Change BUG_ON to WARN_ON
v3:
 (Jani / Tvrtko)
  - Short circuit __i915_sw_fence_init on WARN_ON

Fixes: 62eaf0ae217d ("drm/i915/guc: Support request cancellation")
Signed-off-by: Hugh Dickins <hughd@xxxxxxxxxx>
Signed-off-by: Matthew Brost <matthew.brost@xxxxxxxxx>
Reviewed-by: Matthew Brost <matthew.brost@xxxxxxxxx>
---
 drivers/gpu/drm/i915/gt/intel_context.c |  4 ++--
 drivers/gpu/drm/i915/i915_sw_fence.c    | 17 ++++++++++-------
 2 files changed, 12 insertions(+), 9 deletions(-)

diff --git a/drivers/gpu/drm/i915/gt/intel_context.c b/drivers/gpu/drm/i915/gt/intel_context.c
index ff637147b1a9..e7f78bc7ebfc 100644
--- a/drivers/gpu/drm/i915/gt/intel_context.c
+++ b/drivers/gpu/drm/i915/gt/intel_context.c
@@ -362,8 +362,8 @@ static int __intel_context_active(struct i915_active *active)
 	return 0;
 }
 
-static int sw_fence_dummy_notify(struct i915_sw_fence *sf,
-				 enum i915_sw_fence_notify state)
+static int __i915_sw_fence_call
+sw_fence_dummy_notify(struct i915_sw_fence *sf, enum i915_sw_fence_notify state)
 {
 	return NOTIFY_DONE;
 }
diff --git a/drivers/gpu/drm/i915/i915_sw_fence.c b/drivers/gpu/drm/i915/i915_sw_fence.c
index c589a681da77..08cea73264e7 100644
--- a/drivers/gpu/drm/i915/i915_sw_fence.c
+++ b/drivers/gpu/drm/i915/i915_sw_fence.c
@@ -13,9 +13,9 @@
 #include "i915_selftest.h"
 
 #if IS_ENABLED(CONFIG_DRM_I915_DEBUG)
-#define I915_SW_FENCE_BUG_ON(expr) BUG_ON(expr)
+#define I915_SW_FENCE_WARN_ON(expr) WARN_ON(expr)
 #else
-#define I915_SW_FENCE_BUG_ON(expr) BUILD_BUG_ON_INVALID(expr)
+#define I915_SW_FENCE_WARN_ON(expr) BUILD_BUG_ON_INVALID(expr)
 #endif
 
 static DEFINE_SPINLOCK(i915_sw_fence_lock);
@@ -129,7 +129,10 @@ static int __i915_sw_fence_notify(struct i915_sw_fence *fence,
 	i915_sw_fence_notify_t fn;
 
 	fn = (i915_sw_fence_notify_t)(fence->flags & I915_SW_FENCE_MASK);
-	return fn(fence, state);
+	if (likely(fn))
+		return fn(fence, state);
+	else
+		return 0;
 }
 
 #ifdef CONFIG_DRM_I915_SW_FENCE_DEBUG_OBJECTS
@@ -242,9 +245,9 @@ void __i915_sw_fence_init(struct i915_sw_fence *fence,
 			  const char *name,
 			  struct lock_class_key *key)
 {
-	BUG_ON(!fn || (unsigned long)fn & ~I915_SW_FENCE_MASK);
-
 	__init_waitqueue_head(&fence->wait, name, key);
+	if (WARN_ON(!fn || (unsigned long)fn & ~I915_SW_FENCE_MASK))
+		return;
 	fence->flags = (unsigned long)fn;
 
 	i915_sw_fence_reinit(fence);
@@ -257,8 +260,8 @@ void i915_sw_fence_reinit(struct i915_sw_fence *fence)
 	atomic_set(&fence->pending, 1);
 	fence->error = 0;
 
-	I915_SW_FENCE_BUG_ON(!fence->flags);
-	I915_SW_FENCE_BUG_ON(!list_empty(&fence->wait.head));
+	I915_SW_FENCE_WARN_ON(!fence->flags);
+	I915_SW_FENCE_WARN_ON(!list_empty(&fence->wait.head));
 }
 
 void i915_sw_fence_commit(struct i915_sw_fence *fence)
-- 
2.32.0