linux-kernel - Re: [PATCH 25/48] rcu: Mark writes to rcu_sync ->gp

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Message-ID: <474ae55c-fe9e-4668-8f9b-23f819c76d10@paulmck-laptop>
Date: Fri, 10 May 2024 07:11:05 -0700
From: "Paul E. McKenney" <paulmck@...nel.org>
To: Oleg Nesterov <oleg@...hat.com>
Cc: "Uladzislau Rezki (Sony)" <urezki@...il.com>, RCU <rcu@...r.kernel.org>,
	Neeraj upadhyay <Neeraj.Upadhyay@....com>,
	Boqun Feng <boqun.feng@...il.com>, Hillf Danton <hdanton@...a.com>,
	Joel Fernandes <joel@...lfernandes.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Oleksiy Avramchenko <oleksiy.avramchenko@...y.com>,
	Frederic Weisbecker <frederic@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH 25/48] rcu: Mark writes to rcu_sync ->gp_count field

On Fri, May 10, 2024 at 03:50:57PM +0200, Oleg Nesterov wrote:
> On 05/10, Oleg Nesterov wrote:
> >
> > On 05/07, Paul E. McKenney wrote:
> > >
> > > By the stricter data-race rules used in RCU code [1],
> > ...
> > > [1] https://docs.google.com/document/d/1FwZaXSg3A55ivVoWffA9iMuhJ3_Gmj_E494dLYjjyLQ/edit?usp=sharing
> >
> > I am getting more and more confused...
> >
> > Does this mean that KCSAN/etc treats the files in kernel/rcu/
> > differently than the "Rest of Kernel"? Or what?
> >
> > And how is it enforced?
> 
> I can only find the strnstr(buf, "rcu") checks in skip_report(),
> but they only cover the KCSAN_REPORT_VALUE_CHANGE_ONLY case...

Huh, new one on me!  When I run KCSAN, I set CONFIG_KCSAN_STRICT=y,
which implies CONFIG_KCSAN_REPORT_VALUE_CHANGE_ONLY=n, which should
prevent skip_report() from even being invoked.

Which suggests that in the rest of the kernel, including "rcu_"
in your function name gets you stricter KCSAN checking.  ;-)

							Thanx, Paul