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From:   "Paul E. McKenney" <paulmck@kernel.org>
To:     rcu@vger.kernel.org
Cc:     linux-kernel@vger.kernel.org, kernel-team@fb.com,
        rostedt@goodmis.org, "Paul E. McKenney" <paulmck@kernel.org>,
        Neeraj Upadhyay <quic_neeraju@quicinc.com>,
        Frederic Weisbecker <frederic@kernel.org>,
        Boqun Feng <boqun.feng@gmail.com>,
        Huacai Chen <chenhuacai@kernel.org>,
        WANG Xuerui <kernel@xen0n.name>,
        Thomas Gleixner <tglx@linutronix.de>,
        John Ogness <john.ogness@linutronix.de>,
        Petr Mladek <pmladek@suse.com>, loongarch@lists.linux.dev
Subject: [PATCH RFC v2 rcu 7/8] arch/loongarch: Add ARCH_HAS_NMI_SAFE_THIS_CPU_OPS Kconfig option
Date:   Thu, 29 Sep 2022 11:07:30 -0700
Message-Id: <20220929180731.2875722-7-paulmck@kernel.org>
In-Reply-To: <20220929180714.GA2874192@paulmck-ThinkPad-P17-Gen-1>
References: <20220929180714.GA2874192@paulmck-ThinkPad-P17-Gen-1>
MIME-Version: 1.0
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The loongarch architecture uses the atomic read-modify-write amadd
instruction to implement this_cpu_add(), which is 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/x86/Kconfig,
which will 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@quicinc.com>
Suggested-by: Frederic Weisbecker <frederic@kernel.org>
Suggested-by: Boqun Feng <boqun.feng@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Cc: Huacai Chen <chenhuacai@kernel.org>
Cc: WANG Xuerui <kernel@xen0n.name>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: John Ogness <john.ogness@linutronix.de>
Cc: Petr Mladek <pmladek@suse.com>
Cc: <loongarch@lists.linux.dev>
---
 arch/loongarch/Kconfig | 1 +
 1 file changed, 1 insertion(+)

diff --git a/arch/loongarch/Kconfig b/arch/loongarch/Kconfig
index 4abc9a28aba4..c8864768dc4d 100644
--- a/arch/loongarch/Kconfig
+++ b/arch/loongarch/Kconfig
@@ -10,6 +10,7 @@ config LOONGARCH
 	select ARCH_ENABLE_MEMORY_HOTPLUG
 	select ARCH_ENABLE_MEMORY_HOTREMOVE
 	select ARCH_HAS_ACPI_TABLE_UPGRADE	if ACPI
+	select ARCH_HAS_NMI_SAFE_THIS_CPU_OPS
 	select ARCH_HAS_PHYS_TO_DMA
 	select ARCH_HAS_PTE_SPECIAL
 	select ARCH_HAS_TICK_BROADCAST if GENERIC_CLOCKEVENTS_BROADCAST
-- 
2.31.1.189.g2e36527f23