[PATCHv4 0/2] cpu/hotplug: Keep cpu hotplug disabled until the rebooting cpu is stable

[PATCHv4 0/2] cpu/hotplug: Keep cpu hotplug disabled until the rebooting cpu is stable

[Pingfan Liu]

For the architectures (arm/arm64/ia64/riscv), which relies on the cpu
hot-removing mechanism to implement "kexec -e", it is important to
ensure that the rebooting happens on a valid online cpu. And this logic
should have been guaranteed in migrate_to_reboot_cpu().

But the current code has either contradict (resolved by [2/2]) or
redundancy (resolved by [1/2]) about the logic.


V3 -> V4:
Fix the cpu hotplug enable before kexec-rebooting in powerpc.
Improve commit log and the code's note.

V2 -> V3:
Taking in [2/2], which also has problem with the valid rebooting
cpu. (I had sent three patches for different arches. But maybe it is
better to collapse them into one and collect acks from different arches'
maintainers )

Cc: Eric Biederman <ebiederm@xmission.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vincent Donnefort <vincent.donnefort@arm.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: YueHaibing <yuehaibing@huawei.com>
Cc: Baokun Li <libaokun1@huawei.com>
Cc: Randy Dunlap <rdunlap@infradead.org>
Cc: Valentin Schneider <valentin.schneider@arm.com>
Cc: kexec@lists.infradead.org
Cc: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: Kees Cook <keescook@chromium.org>
Cc: Jens Axboe <axboe@kernel.dk>
To: linux-ia64@vger.kernel.org
Cc: Russell King <linux@armlinux.org.uk>
Cc: Guenter Roeck <linux@roeck-us.net>

Pingfan Liu (2):
  cpu/hotplug: Keep cpu hotplug disabled until the rebooting cpu is
    stable
  cpu/hotplug: Remove the input parameter primary_cpu of
    smp_shutdown_nonboot_cpus()

 arch/arm/kernel/reboot.c          |  2 +-
 arch/arm64/kernel/process.c       |  2 +-
 arch/ia64/kernel/process.c        |  2 +-
 arch/powerpc/kexec/core_64.c      |  1 +
 arch/riscv/kernel/machine_kexec.c |  2 +-
 include/linux/cpu.h               |  4 ++--
 kernel/cpu.c                      | 14 +++++++-------
 kernel/kexec_core.c               | 11 +++++------
 8 files changed, 19 insertions(+), 19 deletions(-)

-- 
2.31.1

[PATCHv4 2/2] cpu/hotplug: Remove the input parameter primary_cpu of smp_shutdown_nonboot_cpus()

[Pingfan Liu]

For all call sites of smp_shutdown_nonboot_cpus(),

$git grep smp_shutdown_nonboot_cpus -- arch | grep -v \*
arch/arm/kernel/reboot.c:94:    smp_shutdown_nonboot_cpus(reboot_cpu);
arch/arm64/kernel/process.c:89: smp_shutdown_nonboot_cpus(reboot_cpu);
arch/ia64/kernel/process.c:578: smp_shutdown_nonboot_cpus(reboot_cpu);
arch/riscv/kernel/machine_kexec.c:135:  smp_shutdown_nonboot_cpus(smp_processor_id());

As it shows, the input parameter seems a little arbitrary.

Since kernel_kexec()->migrate_to_reboot_cpu() has already pinned the
rebooting thread on the selected CPU and the CPU hotplug keeps disabled
before smp_shutdown_nonboot_cpus(). Let smp_shutdown_nonboot_cpus()
deduce the rebooting CPU by smp_processor_id(), instead of passing the
parameter primary_cpu to it.

As a result, all call sites look consistent.

Signed-off-by: Pingfan Liu <kernelfans@gmail.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Kees Cook <keescook@chromium.org>
Cc: Jens Axboe <axboe@kernel.dk>
To: linux-ia64@vger.kernel.org
Cc: Russell King <linux@armlinux.org.uk>
Cc: Guenter Roeck <linux@roeck-us.net>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Wolfram Sang <wsa+renesas@sang-engineering.com>
Cc: Lee Jones <lee.jones@linaro.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Peter Collingbourne <pcc@google.com>
Cc: Marc Zyngier <maz@kernel.org>
To: linux-arm-kernel@lists.infradead.org
Cc: linux-kernel@vger.kernel.org
---
 arch/arm/kernel/reboot.c          | 2 +-
 arch/arm64/kernel/process.c       | 2 +-
 arch/ia64/kernel/process.c        | 2 +-
 arch/riscv/kernel/machine_kexec.c | 2 +-
 include/linux/cpu.h               | 4 ++--
 kernel/cpu.c                      | 4 ++--
 6 files changed, 8 insertions(+), 8 deletions(-)

diff --git a/arch/arm/kernel/reboot.c b/arch/arm/kernel/reboot.c
index 3044fcb8d073..98c961f0b377 100644
--- a/arch/arm/kernel/reboot.c
+++ b/arch/arm/kernel/reboot.c
@@ -91,7 +91,7 @@ void soft_restart(unsigned long addr)
  */
 void machine_shutdown(void)
 {
-	smp_shutdown_nonboot_cpus(reboot_cpu);
+	smp_shutdown_nonboot_cpus();
 }
 
 /*
diff --git a/arch/arm64/kernel/process.c b/arch/arm64/kernel/process.c
index 7fa97df55e3a..1f6498d44740 100644
--- a/arch/arm64/kernel/process.c
+++ b/arch/arm64/kernel/process.c
@@ -86,7 +86,7 @@ void arch_cpu_idle_dead(void)
  */
 void machine_shutdown(void)
 {
-	smp_shutdown_nonboot_cpus(reboot_cpu);
+	smp_shutdown_nonboot_cpus();
 }
 
 /*
diff --git a/arch/ia64/kernel/process.c b/arch/ia64/kernel/process.c
index d7a256bd9d6b..9af53ff43983 100644
--- a/arch/ia64/kernel/process.c
+++ b/arch/ia64/kernel/process.c
@@ -575,7 +575,7 @@ cpu_halt (void)
 
 void machine_shutdown(void)
 {
-	smp_shutdown_nonboot_cpus(reboot_cpu);
+	smp_shutdown_nonboot_cpus();
 
 #ifdef CONFIG_KEXEC
 	kexec_disable_iosapic();
diff --git a/arch/riscv/kernel/machine_kexec.c b/arch/riscv/kernel/machine_kexec.c
index cbef0fc73afa..a30c545714cc 100644
--- a/arch/riscv/kernel/machine_kexec.c
+++ b/arch/riscv/kernel/machine_kexec.c
@@ -132,7 +132,7 @@ void machine_shutdown(void)
 	local_irq_disable();
 
 #if defined(CONFIG_HOTPLUG_CPU)
-	smp_shutdown_nonboot_cpus(smp_processor_id());
+	smp_shutdown_nonboot_cpus();
 #endif
 }
 
diff --git a/include/linux/cpu.h b/include/linux/cpu.h
index 54dc2f9a2d56..0506ba3ac85e 100644
--- a/include/linux/cpu.h
+++ b/include/linux/cpu.h
@@ -127,7 +127,7 @@ extern void cpu_hotplug_enable(void);
 void clear_tasks_mm_cpumask(int cpu);
 int remove_cpu(unsigned int cpu);
 int cpu_device_down(struct device *dev);
-extern void smp_shutdown_nonboot_cpus(unsigned int primary_cpu);
+extern void smp_shutdown_nonboot_cpus(void);
 
 #else /* CONFIG_HOTPLUG_CPU */
 
@@ -140,7 +140,7 @@ static inline void lockdep_assert_cpus_held(void) { }
 static inline void cpu_hotplug_disable(void) { }
 static inline void cpu_hotplug_enable(void) { }
 static inline int remove_cpu(unsigned int cpu) { return -EPERM; }
-static inline void smp_shutdown_nonboot_cpus(unsigned int primary_cpu) { }
+static inline void smp_shutdown_nonboot_cpus(void) { }
 #endif	/* !CONFIG_HOTPLUG_CPU */
 
 #ifdef CONFIG_PM_SLEEP_SMP
diff --git a/kernel/cpu.c b/kernel/cpu.c
index 4415370f0e91..66b8af6b8a3e 100644
--- a/kernel/cpu.c
+++ b/kernel/cpu.c
@@ -1228,7 +1228,7 @@ int remove_cpu(unsigned int cpu)
 }
 EXPORT_SYMBOL_GPL(remove_cpu);
 
-void smp_shutdown_nonboot_cpus(unsigned int primary_cpu)
+void smp_shutdown_nonboot_cpus(void)
 {
 	unsigned int cpu;
 	int error;
@@ -1244,7 +1244,7 @@ void smp_shutdown_nonboot_cpus(unsigned int primary_cpu)
 	__cpu_hotplug_enable();
 
 	for_each_online_cpu(cpu) {
-		if (cpu = primary_cpu)
+		if (cpu = smp_processor_id())
 			continue;
 
 		error = cpu_down_maps_locked(cpu, CPUHP_OFFLINE);
-- 
2.31.1

Re: [PATCHv4 2/2] cpu/hotplug: Remove the input parameter primary_cpu of smp_shutdown_nonboot_cpus()

[Catalin Marinas]

On Thu, May 12, 2022 at 11:06:19AM +0800, Pingfan Liu wrote:
> For all call sites of smp_shutdown_nonboot_cpus(),
> 
> $git grep smp_shutdown_nonboot_cpus -- arch | grep -v \*
> arch/arm/kernel/reboot.c:94:    smp_shutdown_nonboot_cpus(reboot_cpu);
> arch/arm64/kernel/process.c:89: smp_shutdown_nonboot_cpus(reboot_cpu);
> arch/ia64/kernel/process.c:578: smp_shutdown_nonboot_cpus(reboot_cpu);
> arch/riscv/kernel/machine_kexec.c:135:  smp_shutdown_nonboot_cpus(smp_processor_id());
> 
> As it shows, the input parameter seems a little arbitrary.
> 
> Since kernel_kexec()->migrate_to_reboot_cpu() has already pinned the
> rebooting thread on the selected CPU and the CPU hotplug keeps disabled
> before smp_shutdown_nonboot_cpus(). Let smp_shutdown_nonboot_cpus()
> deduce the rebooting CPU by smp_processor_id(), instead of passing the
> parameter primary_cpu to it.
> 
> As a result, all call sites look consistent.
> 
> Signed-off-by: Pingfan Liu <kernelfans@gmail.com>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Cc: Geert Uytterhoeven <geert@linux-m68k.org>
> Cc: Peter Zijlstra <peterz@infradead.org>
> Cc: Kees Cook <keescook@chromium.org>
> Cc: Jens Axboe <axboe@kernel.dk>
> To: linux-ia64@vger.kernel.org
> Cc: Russell King <linux@armlinux.org.uk>
> Cc: Guenter Roeck <linux@roeck-us.net>
> Cc: Arnd Bergmann <arnd@arndb.de>
> Cc: Wolfram Sang <wsa+renesas@sang-engineering.com>
> Cc: Lee Jones <lee.jones@linaro.org>
> Cc: Catalin Marinas <catalin.marinas@arm.com>
> Cc: Will Deacon <will@kernel.org>
> Cc: Mark Rutland <mark.rutland@arm.com>
> Cc: Peter Collingbourne <pcc@google.com>
> Cc: Marc Zyngier <maz@kernel.org>
> To: linux-arm-kernel@lists.infradead.org
> Cc: linux-kernel@vger.kernel.org

For arm64:

Acked-by: Catalin Marinas <catalin.marinas@arm.com>