Convert cpu_up/down to device_online/offline

=============
Changes in v4
=============

	* Split arm and arm64 patches so that the change to use reboot_cpu goes
	  into its own separate patch (Russell)
	* Collected new Acked-by
	* Rebased on top of v5.6-rc6
	* Trimmed the CC list on the cover letter as lists were rejecting it


	git clone git://linux-arm.org/linux-qy.git -b cpu-hp-cleanup-v4


Older post can be found here
----------------------------

	https://lore.kernel.org/lkml/20200223192942.18420-2-qais.yousef@arm.com/


=============
Test Coverage
=============

	All tests ran with LOCKDEP enabled.

Platform: Juno-r2: arm64
------------------------

	* Overnight rcutorture
	* Overnight locktorture
	* kexec -f Image --command="$(cat /proc/cmdline) reboot=s[0-5]"
	* Hibernate to disk (using suspend option)
	* Userspace hotplug via sysfs
	* PSCI firemware checker

Notes:

	* Couldn't convince Juno to hibernate using [reboot] or [shutdown]
	  options.

128 more lines

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@kernel.org>
Signed-off-by: Qais Yousef <redacted>
CC: Thomas Gleixner <redacted>
CC: "Paul E. McKenney" <paulmck@kernel.org>
CC: Helge Deller <deller@gmx.de>
CC: Michael Ellerman <mpe@ellerman.id.au>
CC: "David S. Miller" <davem@davemloft.net>
CC: Juergen Gross <jgross@suse.com>
CC: Mark Rutland <mark.rutland@arm.com>
CC: Lorenzo Pieralisi <redacted>
CC: <redacted>
CC: <redacted>
CC: <redacted>
CC: <redacted>
CC: <redacted>
CC: x86@kernel.org
CC: <redacted>
---
 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

The core device API performs extra housekeeping bits that are missing
from directly calling cpu_up/down.

See commit a6717c01ddc2 ("powerpc/rtas: use device model APIs and
serialization during LPM") for an example description of what might go
wrong.

This also prepares to make cpu_up/down a private interface for anything
but the cpu subsystem.

Acked-by: Michael Ellerman <mpe@ellerman.id.au>
Signed-off-by: Qais Yousef <redacted>
CC: Benjamin Herrenschmidt <benh@kernel.crashing.org>
CC: Paul Mackerras <redacted>
CC: Michael Ellerman <mpe@ellerman.id.au>
CC: Enrico Weigelt <info@metux.net>
CC: Ram Pai <redacted>
CC: Nicholas Piggin <npiggin@gmail.com>
CC: Thiago Jung Bauermann <redacted>
CC: Christophe Leroy <redacted>
CC: Thomas Gleixner <redacted>
CC: <redacted>
CC: <redacted>
---
 arch/powerpc/kexec/core_64.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/powerpc/kexec/core_64.c b/arch/powerpc/kexec/core_64.c
index 04a7cba58eff..b4184092172a 100644
--- a/arch/powerpc/kexec/core_64.c
+++ b/arch/powerpc/kexec/core_64.c

@@ -212,7 +212,7 @@ static void wake_offline_cpus(void)
 		if (!cpu_online(cpu)) {
 			printk(KERN_INFO "kexec: Waking offline cpu %d.\n",
 			       cpu);
-			WARN_ON(cpu_up(cpu));
+			WARN_ON(add_cpu(cpu));
 		}
 	}
 }

-- 
2.17.1

On Mon, Mar 23, 2020 at 01:50:54PM +0000, Qais Yousef wrote:

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@kernel.org>
Signed-off-by: Qais Yousef <redacted>
CC: Thomas Gleixner <redacted>
CC: "Paul E. McKenney" <paulmck@kernel.org>

Reviewed-by: Paul E. McKenney <paulmck@kernel.org>

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