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

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Date:   Thu, 19 May 2022 16:48:21 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Frederic Weisbecker <frederic@...nel.org>
Cc:     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>,
        "Paul E . McKenney" <paulmck@...nel.org>,
        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 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.

No need to speculate on how to solve it; the generic entry code has
alternatives that are good. It's just that reworking your architecture
isn't trivial.