drm/i915: Make i915_gem_context_mark_guilty() safe for unlocked updates

Since we make call i915_gem_context_mark_guilty() concurrently when
resetting different engines in parallel, we need to make sure that our
updates are safe for the unlocked access.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Michel Thierry <michel.thierry@intel.com>
Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Reviewed-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20170721123238.16428-12-chris@chris-wilson.co.uk
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/i915_gem.c

@@ -2740,34 +2740,38 @@ i915_gem_object_pwrite_gtt(struct drm_i915_gem_object *obj,
 	return 0;
 }
 
-static bool ban_context(const struct i915_gem_context *ctx)
+static bool ban_context(const struct i915_gem_context *ctx,
+			unsigned int score)
 {
 	return (i915_gem_context_is_bannable(ctx) &&
-		ctx->ban_score >= CONTEXT_SCORE_BAN_THRESHOLD);
+		score >= CONTEXT_SCORE_BAN_THRESHOLD);
 }
 
 static void i915_gem_context_mark_guilty(struct i915_gem_context *ctx)
 {
-	ctx->guilty_count++;
-	ctx->ban_score += CONTEXT_SCORE_GUILTY;
-	if (ban_context(ctx))
-		i915_gem_context_set_banned(ctx);
+	unsigned int score;
+	bool banned;
 
+	atomic_inc(&ctx->guilty_count);
+
+	score = atomic_add_return(CONTEXT_SCORE_GUILTY, &ctx->ban_score);
+	banned = ban_context(ctx, score);
 	DRM_DEBUG_DRIVER("context %s marked guilty (score %d) banned? %s\n",
-			 ctx->name, ctx->ban_score,
-			 yesno(i915_gem_context_is_banned(ctx)));
-
-	if (!i915_gem_context_is_banned(ctx) || IS_ERR_OR_NULL(ctx->file_priv))
+			 ctx->name, score, yesno(banned));
+	if (!banned)
 		return;
 
-	ctx->file_priv->context_bans++;
-	DRM_DEBUG_DRIVER("client %s has had %d context banned\n",
-			 ctx->name, ctx->file_priv->context_bans);
+	i915_gem_context_set_banned(ctx);
+	if (!IS_ERR_OR_NULL(ctx->file_priv)) {
+		atomic_inc(&ctx->file_priv->context_bans);
+		DRM_DEBUG_DRIVER("client %s has had %d context banned\n",
+				 ctx->name, atomic_read(&ctx->file_priv->context_bans));
+	}
 }
 
 static void i915_gem_context_mark_innocent(struct i915_gem_context *ctx)
 {
-	ctx->active_count++;
+	atomic_inc(&ctx->active_count);
 }
 
 struct drm_i915_gem_request *