linux-kernel - [PATCH v3 02/15] smp: Create a new function to shutdown nonboot cpus

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Date:   Sun, 23 Feb 2020 19:29:29 +0000
From:   Qais Yousef <qais.yousef@....com>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     "Paul E . McKenney" <paulmck@...nel.org>,
        Qais Yousef <qais.yousef@....com>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        Jiri Kosina <jkosina@...e.cz>,
        Nicholas Piggin <npiggin@...il.com>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        Ingo Molnar <mingo@...nel.org>,
        Eiichi Tsukata <devel@...ukata.com>,
        Zhenzhong Duan <zhenzhong.duan@...cle.com>,
        Nadav Amit <namit@...are.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
        Tony Luck <tony.luck@...el.com>,
        Fenghua Yu <fenghua.yu@...el.com>,
        Russell King <linux@...linux.org.uk>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        linux-arm-kernel@...ts.infradead.org, linux-ia64@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH v3 02/15] smp: Create a new function to shutdown nonboot cpus

This function will be used later in machine_shutdown() for some archs.

disable_nonboot_cpus() is not safe to use when doing machine_down(),
because it relies on freeze_secondary_cpus() which in turn is
a suspend/resume related freeze and could abort if the logic detects any
pending activities that can prevent finishing the offlining process.

Signed-off-by: Qais Yousef <qais.yousef@....com>
CC: Thomas Gleixner <tglx@...utronix.de>
CC: Josh Poimboeuf <jpoimboe@...hat.com>
CC: "Peter Zijlstra (Intel)" <peterz@...radead.org>
CC: Jiri Kosina <jkosina@...e.cz>
CC: Nicholas Piggin <npiggin@...il.com>
CC: Daniel Lezcano <daniel.lezcano@...aro.org>
CC: Ingo Molnar <mingo@...nel.org>
CC: Eiichi Tsukata <devel@...ukata.com>
CC: Zhenzhong Duan <zhenzhong.duan@...cle.com>
CC: Nadav Amit <namit@...are.com>
CC: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
CC: "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>
CC: Tony Luck <tony.luck@...el.com>
CC: Fenghua Yu <fenghua.yu@...el.com>
CC: Russell King <linux@...linux.org.uk>
CC: Catalin Marinas <catalin.marinas@....com>
CC: Will Deacon <will@...nel.org>
CC: linux-arm-kernel@...ts.infradead.org
CC: linux-ia64@...r.kernel.org
CC: linux-kernel@...r.kernel.org
---
 include/linux/cpu.h |  2 ++
 kernel/cpu.c        | 42 ++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 44 insertions(+)

diff --git a/include/linux/cpu.h b/include/linux/cpu.h
index cf8cf38dca43..64a246e9c8db 100644
--- a/include/linux/cpu.h
+++ b/include/linux/cpu.h
@@ -120,6 +120,7 @@ extern void cpu_hotplug_enable(void);
 void clear_tasks_mm_cpumask(int cpu);
 int cpu_down(unsigned int cpu);
 int remove_cpu(unsigned int cpu);
+extern void smp_shutdown_nonboot_cpus(unsigned int primary_cpu);
 
 #else /* CONFIG_HOTPLUG_CPU */
 
@@ -131,6 +132,7 @@ static inline int  cpus_read_trylock(void) { return true; }
 static inline void lockdep_assert_cpus_held(void) { }
 static inline void cpu_hotplug_disable(void) { }
 static inline void cpu_hotplug_enable(void) { }
+static inline void smp_shutdown_nonboot_cpus(unsigned int primary_cpu) { }
 #endif	/* !CONFIG_HOTPLUG_CPU */
 
 /* Wrappers which go away once all code is converted */
diff --git a/kernel/cpu.c b/kernel/cpu.c
index 069802f7010f..03c727195b65 100644
--- a/kernel/cpu.c
+++ b/kernel/cpu.c
@@ -1069,6 +1069,48 @@ int remove_cpu(unsigned int cpu)
 }
 EXPORT_SYMBOL_GPL(remove_cpu);
 
+void smp_shutdown_nonboot_cpus(unsigned int primary_cpu)
+{
+	unsigned int cpu;
+	int error;
+
+	cpu_maps_update_begin();
+
+	/*
+	 * Make certain the cpu I'm about to reboot on is online.
+	 *
+	 * This is inline to what migrate_to_reboot_cpu() already do.
+	 */
+	if (!cpu_online(primary_cpu))
+		primary_cpu = cpumask_first(cpu_online_mask);
+
+	for_each_online_cpu(cpu) {
+		if (cpu == primary_cpu)
+			continue;
+
+		error = cpu_down_maps_locked(cpu, CPUHP_OFFLINE);
+		if (error) {
+			pr_err("Failed to offline CPU%d - error=%d",
+				cpu, error);
+			break;
+		}
+	}
+
+	/*
+	 * Ensure all but the reboot CPU are offline.
+	 */
+	BUG_ON(num_online_cpus() > 1);
+
+	/*
+	 * Make sure the CPUs won't be enabled by someone else after this
+	 * point. Kexec will reboot to a new kernel shortly resetting
+	 * everything along the way.
+	 */
+	cpu_hotplug_disabled++;
+
+	cpu_maps_update_done();
+}
+
 #else
 #define takedown_cpu		NULL
 #endif /*CONFIG_HOTPLUG_CPU*/
-- 
2.17.1