drm/i915: fix blank screen booting crashes

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
v4:
 (Lucas)
  - Break WARN_ON changes out in a different patch

Fixes: 62eaf0ae217d ("drm/i915/guc: Support request cancellation")
Signed-off-by: Hugh Dickins <hughd@google.com>
Signed-off-by: Matthew Brost <matthew.brost@intel.com>
Reviewed-by: Matthew Brost <matthew.brost@intel.com>
Signed-off-by: John Harrison <John.C.Harrison@Intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210922015039.26411-1-matthew.brost@intel.com

diff --git a/drivers/gpu/drm/i915/gt/intel_context.c b/drivers/gpu/drm/i915/gt/intel_context.c
index e9a0cad5c34d67ab6f368520621431b8d138c7c6..e1bba4cfc0ffaf58ef524ab76eab0f40850889ff 100644 (file)
--- 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;
 }