From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755231AbbFQOQ2 (ORCPT ); Wed, 17 Jun 2015 10:16:28 -0400 Received: from mail-la0-f45.google.com ([209.85.215.45]:33230 "EHLO mail-la0-f45.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753081AbbFQOQV (ORCPT ); Wed, 17 Jun 2015 10:16:21 -0400 MIME-Version: 1.0 In-Reply-To: <20150617094114.GA3940@gmail.com> References: <1d95640676a92a5ff7382e9c87517c12ea23ccd9.1434485184.git.luto@kernel.org> <20150617094114.GA3940@gmail.com> From: Andy Lutomirski Date: Wed, 17 Jun 2015 07:15:59 -0700 Message-ID: Subject: Re: [RFC/INCOMPLETE 01/13] context_tracking: Add context_tracking_assert_state To: Ingo Molnar Cc: Andy Lutomirski , "Paul E. McKenney" , X86 ML , "linux-kernel@vger.kernel.org" , =?UTF-8?B?RnLDqWTDqXJpYyBXZWlzYmVja2Vy?= , Rik van Riel , Oleg Nesterov , Denys Vlasenko , Borislav Petkov , Kees Cook , Brian Gerst Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Jun 17, 2015 at 2:41 AM, Ingo Molnar wrote: > > * Andy Lutomirski wrote: > >> This will let us sprinkle sanity checks around the kernel without >> making too much of a mess. >> >> Signed-off-by: Andy Lutomirski >> --- >> include/linux/context_tracking.h | 8 ++++++++ >> 1 file changed, 8 insertions(+) >> >> diff --git a/include/linux/context_tracking.h b/include/linux/context_tracking.h >> index 2821838256b4..0fbea4b152e1 100644 >> --- a/include/linux/context_tracking.h >> +++ b/include/linux/context_tracking.h >> @@ -57,6 +57,13 @@ static inline void context_tracking_task_switch(struct task_struct *prev, >> if (context_tracking_is_enabled()) >> __context_tracking_task_switch(prev, next); >> } >> + >> +static inline void context_tracking_assert_state(enum ctx_state state) >> +{ >> + rcu_lockdep_assert(!context_tracking_is_enabled() || >> + this_cpu_read(context_tracking.state) == state, >> + "context tracking state was wrong"); >> +} > > Please don't introduce assert() style debug check interfaces! > > (And RCU should be fixed too I suspect.) > > They are absolutely horrible on the brain when mixed with WARN_ON() interfaces, > which are the dominant runtime check interface in the kernel. > > Instead make it something like: > > #define ct_state() (this_cpu_read(context_tracking.state)) > > #define CT_WARN_ON(cond) \ > WARN_ON(context_tracking_is_enabled() && (cond)) > > and then the debug checks can be written as: > > CT_WARN_ON(ct_state() != CONTEXT_KERNEL); > > This is IMHO _far_ more readable than: > > context_tracking_assert_state(CONTEXT_KERNEL); > > ok? > > (Assuming people will accept 'ct/CT' as an abbreviation for context tracking.) Hmm, ok I guess. The part I don't like is having ct_state() at all on non-context-tracking kernels -- it seems like it's asking for trouble. We could make CT_WARN_ON not even evaluate its argument if !CONFIG_CONTEXT_TRACKING, but then we still have ct_state() returning garbage if !context_tracking_is_enabled(). The assert macro avoids all these problems despite being a bit ugly. It's either a no-op returning void or it does the right thing. --Andy