From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932543AbcHKR2N (ORCPT ); Thu, 11 Aug 2016 13:28:13 -0400 Received: from mail-wm0-f43.google.com ([74.125.82.43]:37488 "EHLO mail-wm0-f43.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752056AbcHKR10 (ORCPT ); Thu, 11 Aug 2016 13:27:26 -0400 From: Roman Pen Cc: Roman Pen , Tejun Heo , linux-kernel@vger.kernel.org Subject: [PATCH 1/1] percpu-refcount: init ->confirm_switch member properly Date: Thu, 11 Aug 2016 19:27:09 +0200 Message-Id: <20160811172709.18442-1-roman.penyaev@profitbricks.com> X-Mailer: git-send-email 2.9.0 To: unlisted-recipients:; (no To-header on input) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org This patch targets two things which are related to ->confirm_switch: 1. Init ->confirm_switch pointer with NULL on percpu_ref_init() or kernel frightfully complains with WARN_ON_ONCE(ref->confirm_switch) at __percpu_ref_switch_to_atomic if memory chunk was not properly zeroed. 2. Warn if RCU callback is still in progress on percpu_ref_exit(). The race still exists, because percpu_ref_call_confirm_rcu() drops ->confirm_switch to NULL early, but that is only a warning and still the caller is responsible that ref is no longer in active use. Hopefully that can help to catch incorrect usage of percpu-refcount. Signed-off-by: Roman Pen Cc: Tejun Heo Cc: linux-kernel@vger.kernel.org --- lib/percpu-refcount.c | 6 ++++++ 1 file changed, 6 insertions(+) diff --git a/lib/percpu-refcount.c b/lib/percpu-refcount.c index 6111bcb..9c110e0 100644 --- a/lib/percpu-refcount.c +++ b/lib/percpu-refcount.c @@ -82,6 +82,7 @@ int percpu_ref_init(struct percpu_ref *ref, percpu_ref_func_t *release, atomic_long_set(&ref->count, start_count); ref->release = release; + ref->confirm_switch = NULL; return 0; } EXPORT_SYMBOL_GPL(percpu_ref_init); @@ -101,6 +102,11 @@ void percpu_ref_exit(struct percpu_ref *ref) unsigned long __percpu *percpu_count = percpu_count_ptr(ref); if (percpu_count) { + /* + * Non-NULL ->confirm_switch is used to indicate that + * switching is in progress. + */ + WARN_ON_ONCE(ref->confirm_switch); free_percpu(percpu_count); ref->percpu_count_ptr = __PERCPU_REF_ATOMIC_DEAD; } -- 2.9.0