Message-ID: <20210718210854.GP4397@paulmck-ThinkPad-P17-Gen-1>
Date:   Sun, 18 Jul 2021 14:08:54 -0700
From:   "Paul E. McKenney" <paulmck@...nel.org>
To:     Zhouyi Zhou <zhouzhouyi@...il.com>
Cc:     Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Josh Triplett <josh@...htriplett.org>,
        rostedt <rostedt@...dmis.org>,
        Lai Jiangshan <jiangshanlai@...il.com>,
        "Joel Fernandes, Google" <joel@...lfernandes.org>,
        rcu <rcu@...r.kernel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>, apw@...onical.com,
        joe@...ches.com, ast@...nel.org, daniel@...earbox.net,
        andrii@...nel.org, kafai@...com, songliubraving@...com, yhs@...com,
        john.fastabend@...il.com, kpsingh@...nel.org, bpf@...r.kernel.org,
        mingo@...nel.org
Subject: Re: [PATCH] RCU: Fix macro name CONFIG_TASKS_RCU_TRACE

On Sun, Jul 18, 2021 at 06:03:34AM +0800, Zhouyi Zhou wrote:
> Hi Paul
> During the research, I found a already existing tool to detect
> undefined Kconfig macro:
> scripts/checkkconfigsymbols.py. It is marvellous!

Nice!  Maybe I should add this to torture.sh.

> By invoking ./scripts/checkkconfigsymbols.py > /tmp/log, I found
> following possibly undefined Kconfig macros
> which may need our attention:
> 
> PREEMPT_LOCK
> Referencing files: include/linux/lockdep_types.h

Not sure about this one.  It might be in anticipation of -rt functionality.
Or another typo.

> PREEMT_DYNAMIC
> Referencing files: kernel/entry/common.c

This needs to be PREEMPT_DYNAMIC.  Please CC Frederic Weisbecker and
myself if you send a patch.

> TREE_PREEMPT_RCU
> Referencing files: arch/sh/configs/sdk7786_defconfig

This would have been correct back in the day.  It should now be
CONFIG_PREEMPT_RCU.  Except that the CONFIG_PREEMPT=y in that same
file implies CONFIG_PREEMPT_RCU=y, so best to simply delete the
CONFIG_TREE_PREEMPT_RCU=y line.

> RCU_CPU_STALL_INFO
> Referencing files: arch/xtensa/configs/nommu_kc705_defconfig

You now get RCU_CPU_STALL_INFO whether you want it or not, so this
line should be deleted.

> RCU_NOCB_CPU_ALL
> Referencing files:
> Documentation/RCU/Design/Memory-Ordering/Tree-RCU-Memory-Ordering.rst

This is an old snapshot of the code.  One approach would be to
update this from the real rcu_prepare_for_idle() function in
kernel/rcu/tree_plugin.h.  The line numbers in the following paragraph
would need to be updated, but the figure is unaffected.

> RCU_TORTURE_TESTS
> Referencing files: kernel/rcu/rcutorture.c

The final "S" needs to be dropped.

> and finally the macro which drive me to do this research
> 
> TASKS_RCU_TRACE
> Referencing files: include/linux/rcupdate.h, kernel/rcu/tree_plugin.h

The fix for this one is of course already queued.

Please CC me if you decide to create patches.  Otherwise, let me know,
and I can produce fixes.

							Thanx, Paul

> On Fri, Jul 16, 2021 at 2:09 AM Paul E. McKenney <paulmck@...nel.org> wrote:
> >
> > On Thu, Jul 15, 2021 at 04:45:04PM +0800, Zhouyi Zhou wrote:
> > > On Thu, Jul 15, 2021 at 11:51 AM Paul E. McKenney <paulmck@...nel.org> wrote:
> > > >
> > > > On Wed, Jul 14, 2021 at 12:44:36PM +0800, Zhouyi Zhou wrote:
> > > > > On Tue, Jul 13, 2021 at 11:19 PM Paul E. McKenney <paulmck@...nel.org> wrote:
> > > > > >
> > > > > > On Tue, Jul 13, 2021 at 06:18:12AM -0700, Paul E. McKenney wrote:
> > > > > > > On Tue, Jul 13, 2021 at 09:09:04AM -0400, Mathieu Desnoyers wrote:
> > > > > > > > ----- On Jul 13, 2021, at 12:16 AM, paulmck paulmck@...nel.org wrote:
> > > > > > > >
> > > > > > > > > On Tue, Jul 13, 2021 at 08:56:45AM +0800, zhouzhouyi@...il.com wrote:
> > > > > > > > >> From: Zhouyi Zhou <zhouzhouyi@...il.com>
> > > > > > > > >>
> > > > > > > > >> Hi Paul,
> > > > > > > > >>
> > > > > > > > >> During my studying of RCU, I did a grep in the kernel source tree.
> > > > > > > > >> I found there are 3 places where the macro name CONFIG_TASKS_RCU_TRACE
> > > > > > > > >> should be CONFIG_TASKS_TRACE_RCU instead.
> > > > > > > > >>
> > > > > > > > >> Without memory fencing, the idle/userspace task inspection may not
> > > > > > > > >> be so accurate.
> > > > > > > > >>
> > > > > > > > >> Thanks for your constant encouragement for my studying.
> > > > > > > > >>
> > > > > > > > >> Best Wishes
> > > > > > > > >> Zhouyi
> > > > > > > > >>
> > > > > > > > >> Signed-off-by: Zhouyi Zhou <zhouzhouyi@...il.com>
> > > > > > > > >
> > > > > > > > > Good eyes, and those could cause real bugs, so thank you!
> > > > > > > >
> > > > > > > > Hi Paul,
> > > > > > > >
> > > > > > > > This makes me wonder: what is missing testing-wise in rcutorture to
> > > > > > > > catch those issues with testing before they reach mainline ?
> > > > > > >
> > > > > > > My guess:  Running on weakly ordered architectures.  ;-)
> > > > > >
> > > > > > And another guess:  A tool that identifies use of Kconfig options
> > > > > > that are not defined in any Kconfig* file.
> > > > > Based on Paul's second guess ;-),  I did a small research, and I think
> > > > > the best answer is to modify scripts/checkpatch.pl. We modify checkpatch.pl
> > > > > to identify use of Kconfig options that are not defined in any Kconfig* file.
> > > > >
> > > > > As I am a C/C++ programmer, I would be glad to take some time to learn
> > > > > perl (checkpatch is implented in perl) first if no other volunteer is
> > > > > about to do it ;-)
> > > >
> > > > I haven't heard anyone else volunteer.  ;-)
> > > >
> > > > Others might have opinions on where best to implement these checks,
> > > > but I must confess that I have not given it much thought.
> > > I recklessly cc the maintainers of checkpatch.pl without your
> > > permission to see others' opion,
> > > and I begin to study perl at the same time, after all, learning
> > > something is always good ;-)
> >
> > Works for me!
> >
> >                                                         Thanx, Paul
> Best Wishes
> Zhouyi

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