From mboxrd@z Thu Jan 1 00:00:00 1970 From: Russell King - ARM Linux admin Date: Tue, 21 Jan 2020 17:03:50 +0000 Subject: Re: [PATCH v2 01/14] smp: Create a new function to shutdown nonboot cpus Message-Id: <20200121170350.GC18808@shell.armlinux.org.uk> List-Id: References: <20191125112754.25223-1-qais.yousef@arm.com> <20191125112754.25223-2-qais.yousef@arm.com> In-Reply-To: <20191125112754.25223-2-qais.yousef@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: Qais Yousef Cc: Thomas Gleixner , Greg Kroah-Hartman , Josh Poimboeuf , "Peter Zijlstra (Intel)" , Jiri Kosina , Nicholas Piggin , Daniel Lezcano , Ingo Molnar , Eiichi Tsukata , Zhenzhong Duan , Nadav Amit , "Rafael J. Wysocki" , Tony Luck , Fenghua Yu , Catalin Marinas , Will Deacon , linux-arm-kernel@lists.infradead.org, linux-ia64@vger.kernel.org, linux-kernel@vger.kernel.org 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 > CC: Thomas Gleixner > CC: Josh Poimboeuf > CC: "Peter Zijlstra (Intel)" > CC: Jiri Kosina > CC: Nicholas Piggin > CC: Daniel Lezcano > CC: Ingo Molnar > CC: Eiichi Tsukata > CC: Zhenzhong Duan > CC: Nadav Amit > CC: Greg Kroah-Hartman > CC: "Rafael J. Wysocki" > CC: Tony Luck > CC: Fenghua Yu > CC: Russell King > CC: Catalin Marinas > CC: Will Deacon > 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? -- RMK's Patch system: https://www.armlinux.org.uk/developer/patches/ FTTC broadband for 0.8mile line in suburbia: sync at 12.1Mbps down 622kbps up According to speedtest.net: 11.9Mbps down 500kbps up