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_drv.h

@@ -602,7 +602,7 @@ struct drm_i915_file_private {
  * to limit the badly behaving clients access to gpu.
  */
 #define I915_MAX_CLIENT_CONTEXT_BANS 3
-	int context_bans;
+	atomic_t context_bans;
 };
 
 /* Used by dp and fdi links */

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;
 
-	DRM_DEBUG_DRIVER("context %s marked guilty (score %d) banned? %s\n",
-			 ctx->name, ctx->ban_score,
-			 yesno(i915_gem_context_is_banned(ctx)));
+	atomic_inc(&ctx->guilty_count);
 
-	if (!i915_gem_context_is_banned(ctx) || IS_ERR_OR_NULL(ctx->file_priv))
+	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, 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 *

drivers/gpu/drm/i915/i915_gem_context.c

@@ -977,7 +977,7 @@ int i915_gem_switch_to_kernel_context(struct drm_i915_private *dev_priv)
 
 static bool client_is_banned(struct drm_i915_file_private *file_priv)
 {
-	return file_priv->context_bans > I915_MAX_CLIENT_CONTEXT_BANS;
+	return atomic_read(&file_priv->context_bans) > I915_MAX_CLIENT_CONTEXT_BANS;
 }
 
 int i915_gem_context_create_ioctl(struct drm_device *dev, void *data,
@@ -1179,8 +1179,8 @@ int i915_gem_context_reset_stats_ioctl(struct drm_device *dev,
 	else
 		args->reset_count = 0;
 
-	args->batch_active = READ_ONCE(ctx->guilty_count);
-	args->batch_pending = READ_ONCE(ctx->active_count);
+	args->batch_active = atomic_read(&ctx->guilty_count);
+	args->batch_pending = atomic_read(&ctx->active_count);
 
 	ret = 0;
 out:

drivers/gpu/drm/i915/i915_gem_context.h

@@ -191,17 +191,17 @@ struct i915_gem_context {
 	u32 desc_template;
 
 	/** guilty_count: How many times this context has caused a GPU hang. */
-	unsigned int guilty_count;
+	atomic_t guilty_count;
 	/**
 	 * @active_count: How many times this context was active during a GPU
 	 * hang, but did not cause it.
 	 */
-	unsigned int active_count;
+	atomic_t active_count;
 
 #define CONTEXT_SCORE_GUILTY		10
 #define CONTEXT_SCORE_BAN_THRESHOLD	40
 	/** ban_score: Accumulated score of all hangs caused by this context. */
-	int ban_score;
+	atomic_t ban_score;
 
 	/** remap_slice: Bitmask of cache lines that need remapping */
 	u8 remap_slice;

drivers/gpu/drm/i915/i915_gem_request.c

@@ -374,8 +374,7 @@ static void i915_gem_request_retire(struct drm_i915_gem_request *request)
 	i915_gem_request_remove_from_client(request);
 
 	/* Retirement decays the ban score as it is a sign of ctx progress */
-	if (request->ctx->ban_score > 0)
-		request->ctx->ban_score--;
+	atomic_dec_if_positive(&request->ctx->ban_score);
 
 	/* The backing object for the context is done after switching to the
 	 * *next* context. Therefore we cannot retire the previous context until

drivers/gpu/drm/i915/i915_gpu_error.c

@@ -1266,7 +1266,7 @@ static void record_request(struct drm_i915_gem_request *request,
 			   struct drm_i915_error_request *erq)
 {
 	erq->context = request->ctx->hw_id;
-	erq->ban_score = request->ctx->ban_score;
+	erq->ban_score = atomic_read(&request->ctx->ban_score);
 	erq->seqno = request->global_seqno;
 	erq->jiffies = request->emitted_jiffies;
 	erq->head = request->head;
@@ -1357,9 +1357,9 @@ static void record_context(struct drm_i915_error_context *e,
 
 	e->handle = ctx->user_handle;
 	e->hw_id = ctx->hw_id;
-	e->ban_score = ctx->ban_score;
-	e->guilty = ctx->guilty_count;
-	e->active = ctx->active_count;
+	e->ban_score = atomic_read(&ctx->ban_score);
+	e->guilty = atomic_read(&ctx->guilty_count);
+	e->active = atomic_read(&ctx->active_count);
 }
 
 static void request_record_user_bo(struct drm_i915_gem_request *request,