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

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Date: Sun, 12 May 2024 12:41:52 +0200
From: Oleg Nesterov <oleg@...hat.com>
To: "Paul E. McKenney" <paulmck@...nel.org>
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

Sorry for another delay...

On 05/10, Paul E. McKenney wrote:
>
> On Fri, May 10, 2024 at 03:50:57PM +0200, Oleg Nesterov wrote:
> >
> > 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.  ;-)

Yes.

And that is why I was very confused. I misinterpreted the "stricter
data-race rules used in RCU code" as if there must be more "rcu-only"
hacks in the kernel/kcsan/ code which I can't find ;)

Oleg.