Re: [PATCH v2 01/14] smp: Create a new function to shutdown nonboot cpus

Russell King - ARM Linux admin
2020-01-21T17:04:51Z

On Mon, Nov 25, 2019 at 11:27:41AM +0000, Qais Yousef wrote:
> This function will be used later in machine_shutdown() for some archs.
>
> Signed-off-by: Qais Yousef <qais.yousef@arm.com>
> CC: Thomas Gleixner <tglx@linutronix.de>
> CC: Josh Poimboeuf <jpoimboe@redhat.com>
> CC: "Peter Zijlstra (Intel)" <peterz@infradead.org>
> CC: Jiri Kosina <jkosina@suse.cz>
> CC: Nicholas Piggin <npiggin@gmail.com>
> CC: Daniel Lezcano <daniel.lezcano@linaro.org>
> CC: Ingo Molnar <mingo@kernel.org>
> CC: Eiichi Tsukata <devel@etsukata.com>
> CC: Zhenzhong Duan <zhenzhong.duan@oracle.com>
> CC: Nadav Amit <namit@vmware.com>
> CC: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> CC: "Rafael J. Wysocki" <rafael.j.wysocki@intel.com>
> CC: Tony Luck <tony.luck@intel.com>
> CC: Fenghua Yu <fenghua.yu@intel.com>
> CC: Russell King <linux@armlinux.org.uk>
> CC: Catalin Marinas <catalin.marinas@arm.com>
> CC: Will Deacon <will@kernel.org>
> CC: linux-arm-kernel@lists.infradead.org
> CC: linux-ia64@vger.kernel.org
> CC: linux-kernel@vger.kernel.org
> ---
> include/linux/cpu.h | 2 ++
> kernel/cpu.c | 17 +++++++++++++++++
> 2 files changed, 19 insertions(+)
>
> diff --git a/include/linux/cpu.h b/include/linux/cpu.h
> index bc6c879bd110..8229932fb053 100644
> --- a/include/linux/cpu.h
> +++ b/include/linux/cpu.h
> @@ -118,6 +118,7 @@ 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);
> +extern void smp_shutdown_nonboot_cpus(unsigned int primary_cpu);
>
> #else /* CONFIG_HOTPLUG_CPU */
>
> @@ -129,6 +130,7 @@ 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 e2cad3ee2ead..94055a0d989e 100644
> --- a/kernel/cpu.c
> +++ b/kernel/cpu.c
> @@ -1058,6 +1058,23 @@ int cpu_down(unsigned int cpu)
> }
> EXPORT_SYMBOL(cpu_down);
>
> +void smp_shutdown_nonboot_cpus(unsigned int primary_cpu)
> +{
> + unsigned int cpu;
> +
> + if (!cpu_online(primary_cpu)) {
> + pr_info("Attempting to shutdodwn nonboot cpus while boot cpu is offline!\n");
> + cpu_online(primary_cpu);
> + }
> +
> + for_each_present_cpu(cpu) {
> + if (cpu == primary_cpu)
> + continue;
> + if (cpu_online(cpu))
> + cpu_down(cpu);
> + }

How does this avoid racing with userspace attempting to restart CPUs
that have already been taken down by this function?

--
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