linux-kernel - Re: [PATCH 02/20] context_tracking: Add a note about noinstr VS unsafe context tracking functions

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Date:   Thu, 9 Jun 2022 12:50:13 +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 02/20] context_tracking: Add a note about noinstr VS
 unsafe context tracking functions

On Wed, Jun 08, 2022 at 04:40:19PM +0200, Frederic Weisbecker wrote:
> +/*
> + * OBSOLETE:
> + * This function should be noinstr but the below local_irq_restore() is
> + * unsafe because it involves illegal RCU uses through tracing and lockdep.
> + * This is unlikely to be fixed as this function is obsolete. The preferred
> + * way is to call __context_tracking_enter() through user_enter_irqoff()
> + * or context_tracking_guest_enter(). It should be the arch entry code
> + * responsibility to call into context tracking with IRQs disabled.
> +
> + */

whitespace fail there, methinks.

>  void context_tracking_enter(enum ctx_state state)
>  {
>  	unsigned long flags;