drm/i915/gem: Embed context/timeline name inside the GEM context

Use a small char buffer inside the i915_gem_context to store the user
friendly name so that ctx->name has the same lifetime as the RCU
protected GEM context. That is, e.g. when using print_request() that
prints the timeline name (ctx->name), the name will not be prematurely
freed upon the context being closed and the last reference dropped.
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Cc: Matthew Auld <matthew.auld@intel.com>
Reviewed-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20191111114323.5833-2-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/gem/i915_gem_context.c

@@ -277,9 +277,7 @@ static void i915_gem_context_free(struct i915_gem_context *ctx)
 	if (ctx->timeline)
 		intel_timeline_put(ctx->timeline);
 
-	kfree(ctx->name);
 	put_pid(ctx->pid);
-
 	mutex_destroy(&ctx->mutex);
 
 	kfree_rcu(ctx, rcu);
@@ -789,12 +787,8 @@ static int gem_context_register(struct i915_gem_context *ctx,
 	mutex_unlock(&ctx->mutex);
 
 	ctx->pid = get_task_pid(current, PIDTYPE_PID);
-	ctx->name = kasprintf(GFP_KERNEL, "%s[%d]",
+	snprintf(ctx->name, sizeof(ctx->name), "%s[%d]",
 		 current->comm, pid_nr(ctx->pid));
-	if (!ctx->name) {
-		ret = -ENOMEM;
-		goto err_pid;
-	}
 
 	/* And finally expose ourselves to userspace via the idr */
 	mutex_lock(&fpriv->context_idr_lock);
@@ -803,8 +797,6 @@ static int gem_context_register(struct i915_gem_context *ctx,
 	if (ret >= 0)
 		goto out;
 
-	kfree(fetch_and_zero(&ctx->name));
-err_pid:
 	put_pid(fetch_and_zero(&ctx->pid));
 out:
 	return ret;

drivers/gpu/drm/i915/gem/i915_gem_context_types.h

@@ -100,15 +100,6 @@ struct i915_gem_context {
 	 */
 	struct pid *pid;
 
-	/**
-	 * @name: arbitrary name
-	 *
-	 * A name is constructed for the context from the creator's process
-	 * name, pid and user handle in order to uniquely identify the
-	 * context in messages.
-	 */
-	const char *name;
-
 	/** link: place with &drm_i915_private.context_list */
 	struct list_head link;
 	struct llist_node free_link;
@@ -176,6 +167,15 @@ struct i915_gem_context {
 	 * per vm, which may be one per context or shared with the global GTT)
 	 */
 	struct radix_tree_root handles_vma;
+
+	/**
+	 * @name: arbitrary name, used for user debug
+	 *
+	 * A name is constructed for the context from the creator's process
+	 * name, pid and user handle in order to uniquely identify the
+	 * context in messages.
+	 */
+	char name[TASK_COMM_LEN + 8];
 };
 
 #endif /* __I915_GEM_CONTEXT_TYPES_H__ */

drivers/gpu/drm/i915/gem/selftests/mock_context.c

@@ -37,9 +37,7 @@ mock_context(struct drm_i915_private *i915,
 	if (name) {
 		struct i915_ppgtt *ppgtt;
 
-		ctx->name = kstrdup(name, GFP_KERNEL);
-		if (!ctx->name)
-			goto err_put;
+		strncpy(ctx->name, name, sizeof(ctx->name));
 
 		ppgtt = mock_ppgtt(i915, name);
 		if (!ppgtt)