drm/i915: Taint (TAINT_WARN) the kernel if the GPU reset fails

History tells us that if we cannot reset the GPU now, we never will. This
then impacts everything that is run subsequently. On failing the reset,
we mark the driver as wedged, trying to prevent further execution on the
GPU, forcing userspace to fallback to using the CPU to update its
framebuffers and let the user know what happened.

We also want to go one step further and add a taint to the kernel so that
any subsequent faults can be traced back to this failure. This is
useful for CI, where if the GPU/driver fails we want to reboot and
restart testing rather than continue on into oblivion. For everyone
else, the warning taint is a testament to the system unreliability.

TAINT_WARN is used anytime a WARN() is emitted, which is suitable for
our purposes here as well; the driver/system may behave unexpectedly
after the failure.

v2: Also taint if the recovery fails (again history shows us that is
typically fatal).
v3: Use TAINT_WARN

References: https://bugs.freedesktop.org/show_bug.cgi?id=103514
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Michał Winiarski <michal.winiarski@intel.com>
Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Acked-by: Tomi Sarvela <tomi.p.sarvela@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20171205172757.32609-1-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/i915_drv.c

@@ -1897,9 +1897,9 @@ void i915_reset(struct drm_i915_private *i915, unsigned int flags)
 	disable_irq(i915->drm.irq);
 	ret = i915_gem_reset_prepare(i915);
 	if (ret) {
-		DRM_ERROR("GPU recovery failed\n");
+		dev_err(i915->drm.dev, "GPU recovery failed\n");
 		intel_gpu_reset(i915, ALL_ENGINES);
-		goto error;
+		goto taint;
 	}
 
 	if (!intel_has_gpu_reset(i915)) {
@@ -1916,7 +1916,7 @@ void i915_reset(struct drm_i915_private *i915, unsigned int flags)
 	}
 	if (ret) {
 		dev_err(i915->drm.dev, "Failed to reset chip\n");
-		goto error;
+		goto taint;
 	}
 
 	i915_gem_reset(i915);
@@ -1959,6 +1959,20 @@ wakeup:
 	wake_up_bit(&error->flags, I915_RESET_HANDOFF);
 	return;
 
+taint:
+	/*
+	 * History tells us that if we cannot reset the GPU now, we
+	 * never will. This then impacts everything that is run
+	 * subsequently. On failing the reset, we mark the driver
+	 * as wedged, preventing further execution on the GPU.
+	 * We also want to go one step further and add a taint to the
+	 * kernel so that any subsequent faults can be traced back to
+	 * this failure. This is important for CI, where if the
+	 * GPU/driver fails we would like to reboot and restart testing
+	 * rather than continue on into oblivion. For everyone else,
+	 * the system should still plod along, but they have been warned!
+	 */
+	add_taint(TAINT_WARN, LOCKDEP_STILL_OK);
 error:
 	i915_gem_set_wedged(i915);
 	i915_gem_retire_requests(i915);