linux-kernel - Re: [PATCH v3 rcu 08/11] arch/s390: Add ARCH_HAS_NMI_SAFE_THIS_CPU

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Message-ID: <Y1D4aYbjRJjUEelZ@osiris>
Date:   Thu, 20 Oct 2022 09:27:37 +0200
From:   Heiko Carstens <hca@...ux.ibm.com>
To:     Heiko Carstens <hca@...ux.ibm.com>
Cc:     Christian Borntraeger <borntraeger@...ux.ibm.com>,
        "Paul E. McKenney" <paulmck@...nel.org>, rcu@...r.kernel.org,
        linux-kernel@...r.kernel.org, kernel-team@...com,
        rostedt@...dmis.org, Neeraj Upadhyay <quic_neeraju@...cinc.com>,
        Frederic Weisbecker <frederic@...nel.org>,
        Boqun Feng <boqun.feng@...il.com>,
        Vasily Gorbik <gor@...ux.ibm.com>,
        Alexander Gordeev <agordeev@...ux.ibm.com>,
        Sven Schnelle <svens@...ux.ibm.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        John Ogness <john.ogness@...utronix.de>,
        Petr Mladek <pmladek@...e.com>, linux-s390@...r.kernel.org
Subject: Re: [PATCH v3 rcu 08/11] arch/s390: Add
 ARCH_HAS_NMI_SAFE_THIS_CPU_OPS Kconfig option

On Thu, Oct 20, 2022 at 09:23:49AM +0200, Heiko Carstens wrote:
> On Thu, Oct 20, 2022 at 07:16:44AM +0200, Christian Borntraeger wrote:
> > Am 20.10.22 um 00:58 schrieb Paul E. McKenney:
> > > The s390 architecture uses either a cmpxchg loop (old systems)
> > > or the laa add-to-memory instruction (new systems) to implement
> > > this_cpu_add(), both of which are NMI safe.  This means that the old
> > > and more-efficient srcu_read_lock() may be used in NMI context, without
> > > the need for srcu_read_lock_nmisafe().  Therefore, add the new Kconfig
> > > option ARCH_HAS_NMI_SAFE_THIS_CPU_OPS to arch/arm64/Kconfig, which will
> > 						s390 ?

Ah, this typo is what Christian pointed out; missed that.

> > > cause NEED_SRCU_NMI_SAFE to be deselected, thus preserving the current
> > > srcu_read_lock() behavior.
> > > 
> > > Link: https://lore.kernel.org/all/20220910221947.171557773@linutronix.de/
> > > 
> > > Suggested-by: Neeraj Upadhyay <quic_neeraju@...cinc.com>
> > > Suggested-by: Frederic Weisbecker <frederic@...nel.org>
> > > Suggested-by: Boqun Feng <boqun.feng@...il.com>
> > > Signed-off-by: Paul E. McKenney <paulmck@...nel.org>
> ...
> > > ---
> > >   arch/s390/Kconfig | 1 +
> > >   1 file changed, 1 insertion(+)
> 
> Not sure what Christian was trying to say with his empty reply :)
> In any case:
> Acked-by: Heiko Carstens <hca@...ux.ibm.com>