drm/i915: Show i915_gem_context owner in debugfs

Print the context's owner (via the pid under file_priv) under debugfs.
In doing so, we must be careful that the filp is not accessed after it
is freed (notified via i915_gem_context_close).

v2: Mark the file_priv as closed.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1464098023-3294-6-git-send-email-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/i915_debugfs.c

@@ -2014,9 +2014,23 @@ static int i915_context_status(struct seq_file *m, void *unused)
 			continue;
 
 		seq_printf(m, "HW context %u ", ctx->hw_id);
+		if (IS_ERR(ctx->file_priv)) {
+			seq_puts(m, "(deleted) ");
+		} else if (ctx->file_priv) {
+			struct pid *pid = ctx->file_priv->file->pid;
+			struct task_struct *task;
+
+			task = get_pid_task(pid, PIDTYPE_PID);
+			if (task) {
+				seq_printf(m, "(%s [%d]) ",
+					   task->comm, task->pid);
+				put_task_struct(task);
+			}
+		} else {
+			seq_puts(m, "(kernel) ");
+		}
+
 		describe_ctx(m, ctx);
-		if (ctx == dev_priv->kernel_context)
-			seq_printf(m, "(kernel context) ");
 
 		if (i915.enable_execlists) {
 			seq_putc(m, '\n');

drivers/gpu/drm/i915/i915_gem_context.c

@@ -468,6 +468,7 @@ static int context_idr_cleanup(int id, void *p, void *data)
 {
 	struct i915_gem_context *ctx = p;
 
+	ctx->file_priv = ERR_PTR(-EBADF);
 	i915_gem_context_unreference(ctx);
 	return 0;
 }
@@ -938,7 +939,7 @@ int i915_gem_context_destroy_ioctl(struct drm_device *dev, void *data,
 		return PTR_ERR(ctx);
 	}
 
-	idr_remove(&ctx->file_priv->context_idr, ctx->user_handle);
+	idr_remove(&file_priv->context_idr, ctx->user_handle);
 	i915_gem_context_unreference(ctx);
 	mutex_unlock(&dev->struct_mutex);