linux-kernel - Re: [PATCH 03/21] rcu: Add a note about noinstr VS unsafe eqs functions

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Message-ID: <20220519152611.GY1790663@paulmck-ThinkPad-P17-Gen-1>
Date:   Thu, 19 May 2022 08:26:11 -0700
From:   "Paul E. McKenney" <paulmck@...nel.org>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Frederic Weisbecker <frederic@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Phil Auld <pauld@...hat.com>,
        Alex Belits <abelits@...vell.com>,
        Nicolas Saenz Julienne <nsaenz@...nel.org>,
        Xiongfeng Wang <wangxiongfeng2@...wei.com>,
        Neeraj Upadhyay <quic_neeraju@...cinc.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Yu Liao <liaoyu15@...wei.com>,
        Boqun Feng <boqun.feng@...il.com>,
        Marcelo Tosatti <mtosatti@...hat.com>,
        Paul Gortmaker <paul.gortmaker@...driver.com>,
        Uladzislau Rezki <uladzislau.rezki@...y.com>,
        Joel Fernandes <joel@...lfernandes.org>
Subject: Re: [PATCH 03/21] rcu: Add a note about noinstr VS unsafe eqs
 functions

On Thu, May 19, 2022 at 04:54:38PM +0200, Peter Zijlstra wrote:
> On Tue, May 03, 2022 at 12:00:33PM +0200, Frederic Weisbecker wrote:
> > Some RCU functions enter or exit into/from RCU idle mode while using
> > trace-able and lockdep-aware IRQs (un-)masking. This could be easily
> > solved with using raw versions of local_irq_*() but we would then
> > lose some precious debugging informations.
> > 
> > Another possible way to solve this may consist in using rude RCU-tasks
> > in lockdep and irqsoff tracing.
> > 
> > In any case and until this get solved, those RCU functions can't get
> > tagged as noinstr even though they should.
> 
> FWIW, this also means RCU_NONIDLE() is broken. Luckily there aren't many
> users left.

More to the point, rcu_irq_enter_irqson() and rcu_irq_exit_irqson() need
the same help that rcu_idle_enter() and rcu_idle_exit() got earlier this
week [1], independent of RCU_NONIDLE().

Unless Frederic beats me to it, I will queue something up.

							Thanx, Paul

[1] https://lore.kernel.org/all/20220518162118.GA2661055@paulmck-ThinkPad-P17-Gen-1/