linux-kernel - [PATCH v4 01/17] cpu: Add new {add,remove}

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Date:   Mon, 23 Mar 2020 13:50:54 +0000
From:   Qais Yousef <qais.yousef@....com>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     linux-kernel@...r.kernel.org, Qais Yousef <qais.yousef@....com>,
        "Paul E. McKenney" <paulmck@...nel.org>,
        Helge Deller <deller@....de>,
        Michael Ellerman <mpe@...erman.id.au>,
        "David S. Miller" <davem@...emloft.net>,
        Juergen Gross <jgross@...e.com>,
        Mark Rutland <mark.rutland@....com>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        xen-devel@...ts.xenproject.org, linux-parisc@...r.kernel.org,
        sparclinux@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        linux-arm-kernel@...ts.infradead.org, x86@...nel.org
Subject: [PATCH v4 01/17] cpu: Add new {add,remove}_cpu() functions

The new functions use device_{online,offline}() which are userspace
safe.

This is in preparation to move cpu_{up, down} kernel users to use
a safer interface that is not racy with userspace.

Suggested-by: "Paul E. McKenney" <paulmck@...nel.org>
Signed-off-by: Qais Yousef <qais.yousef@....com>
CC: Thomas Gleixner <tglx@...utronix.de>
CC: "Paul E. McKenney" <paulmck@...nel.org>
CC: Helge Deller <deller@....de>
CC: Michael Ellerman <mpe@...erman.id.au>
CC: "David S. Miller" <davem@...emloft.net>
CC: Juergen Gross <jgross@...e.com>
CC: Mark Rutland <mark.rutland@....com>
CC: Lorenzo Pieralisi <lorenzo.pieralisi@....com>
CC: xen-devel@...ts.xenproject.org
CC: linux-parisc@...r.kernel.org
CC: sparclinux@...r.kernel.org
CC: linuxppc-dev@...ts.ozlabs.org
CC: linux-arm-kernel@...ts.infradead.org
CC: x86@...nel.org
CC: linux-kernel@...r.kernel.org
---
 include/linux/cpu.h |  2 ++
 kernel/cpu.c        | 24 ++++++++++++++++++++++++
 2 files changed, 26 insertions(+)

diff --git a/include/linux/cpu.h b/include/linux/cpu.h
index 1ca2baf817ed..cf8cf38dca43 100644
--- a/include/linux/cpu.h
+++ b/include/linux/cpu.h
@@ -89,6 +89,7 @@ extern ssize_t arch_cpu_release(const char *, size_t);
 #ifdef CONFIG_SMP
 extern bool cpuhp_tasks_frozen;
 int cpu_up(unsigned int cpu);
+int add_cpu(unsigned int cpu);
 void notify_cpu_starting(unsigned int cpu);
 extern void cpu_maps_update_begin(void);
 extern void cpu_maps_update_done(void);
@@ -118,6 +119,7 @@ extern void cpu_hotplug_disable(void);
 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);
 
 #else /* CONFIG_HOTPLUG_CPU */
 
diff --git a/kernel/cpu.c b/kernel/cpu.c
index 9c706af713fb..069802f7010f 100644
--- a/kernel/cpu.c
+++ b/kernel/cpu.c
@@ -1057,6 +1057,18 @@ int cpu_down(unsigned int cpu)
 }
 EXPORT_SYMBOL(cpu_down);
 
+int remove_cpu(unsigned int cpu)
+{
+	int ret;
+
+	lock_device_hotplug();
+	ret = device_offline(get_cpu_device(cpu));
+	unlock_device_hotplug();
+
+	return ret;
+}
+EXPORT_SYMBOL_GPL(remove_cpu);
+
 #else
 #define takedown_cpu		NULL
 #endif /*CONFIG_HOTPLUG_CPU*/
@@ -1209,6 +1221,18 @@ int cpu_up(unsigned int cpu)
 }
 EXPORT_SYMBOL_GPL(cpu_up);
 
+int add_cpu(unsigned int cpu)
+{
+	int ret;
+
+	lock_device_hotplug();
+	ret = device_online(get_cpu_device(cpu));
+	unlock_device_hotplug();
+
+	return ret;
+}
+EXPORT_SYMBOL_GPL(add_cpu);
+
 #ifdef CONFIG_PM_SLEEP_SMP
 static cpumask_var_t frozen_cpus;
 
-- 
2.17.1