8 files changed, 221 insertions, 29 deletions

diff --git a/arch/i386/Kconfig b/arch/i386/Kconfig
index d4ae5f9ceae6..b4cd11e58451 100644
--- a/arch/i386/Kconfig
+++ b/arch/i386/Kconfig
@@ -1250,6 +1250,15 @@ config SCx200
           This support is also available as a module.  If compiled as a
           module, it will be called scx200.
 
+config HOTPLUG_CPU
+        bool "Support for hot-pluggable CPUs (EXPERIMENTAL)"
+        depends on SMP && HOTPLUG && EXPERIMENTAL
+        ---help---
+          Say Y here to experiment with turning CPUs off and on.  CPUs
+          can be controlled through /sys/devices/system/cpu.
+
+          Say N.
+
 source "drivers/pcmcia/Kconfig"
 
 source "drivers/pci/hotplug/Kconfig"
diff --git a/arch/i386/kernel/apic.c b/arch/i386/kernel/apic.c
index 8d993fa71754..a28a088f3e75 100644
--- a/arch/i386/kernel/apic.c
+++ b/arch/i386/kernel/apic.c
@@ -26,6 +26,7 @@
 #include <linux/mc146818rtc.h>
 #include <linux/kernel_stat.h>
 #include <linux/sysdev.h>
+#include <linux/cpu.h>
 
 #include <asm/atomic.h>
 #include <asm/smp.h>
@@ -1048,7 +1049,7 @@ void __init setup_secondary_APIC_clock(void)
         setup_APIC_timer(calibration_result);
 }
 
-void __init disable_APIC_timer(void)
+void __devinit disable_APIC_timer(void)
 {
         if (using_apic_timer) {
                 unsigned long v;
diff --git a/arch/i386/kernel/io_apic.c b/arch/i386/kernel/io_apic.c
index 08540bc4ba3e..3c2b3bdfc807 100644
--- a/arch/i386/kernel/io_apic.c
+++ b/arch/i386/kernel/io_apic.c
@@ -576,9 +576,11 @@ static int balanced_irq(void *unused)
                 try_to_freeze(PF_FREEZE);
                 if (time_after(jiffies,
                                 prev_balance_time+balanced_irq_interval)) {
+                        preempt_disable();
                         do_irq_balance();
                         prev_balance_time = jiffies;
                         time_remaining = balanced_irq_interval;
+                        preempt_enable();
                 }
         }
         return 0;
diff --git a/arch/i386/kernel/irq.c b/arch/i386/kernel/irq.c
index 73945a3c53c4..af115004aec5 100644
--- a/arch/i386/kernel/irq.c
+++ b/arch/i386/kernel/irq.c
@@ -15,6 +15,9 @@
 #include <linux/seq_file.h>
 #include <linux/interrupt.h>
 #include <linux/kernel_stat.h>
+#include <linux/notifier.h>
+#include <linux/cpu.h>
+#include <linux/delay.h>
 
 DEFINE_PER_CPU(irq_cpustat_t, irq_stat) ____cacheline_maxaligned_in_smp;
 EXPORT_PER_CPU_SYMBOL(irq_stat);
@@ -210,9 +213,8 @@ int show_interrupts(struct seq_file *p, void *v)
 
         if (i == 0) {
                 seq_printf(p, "           ");
-                for (j=0; j<NR_CPUS; j++)
-                        if (cpu_online(j))
-                                seq_printf(p, "CPU%d       ",j);
+                for_each_cpu(j)
+                        seq_printf(p, "CPU%d       ",j);
                 seq_putc(p, '\n');
         }
 
@@ -225,9 +227,8 @@ int show_interrupts(struct seq_file *p, void *v)
 #ifndef CONFIG_SMP
                 seq_printf(p, "%10u ", kstat_irqs(i));
 #else
-                for (j = 0; j < NR_CPUS; j++)
-                        if (cpu_online(j))
-                                seq_printf(p, "%10u ", kstat_cpu(j).irqs[i]);
+                for_each_cpu(j)
+                        seq_printf(p, "%10u ", kstat_cpu(j).irqs[i]);
 #endif
                 seq_printf(p, " %14s", irq_desc[i].handler->typename);
                 seq_printf(p, "  %s", action->name);
@@ -240,16 +241,14 @@ skip:
                 spin_unlock_irqrestore(&irq_desc[i].lock, flags);
         } else if (i == NR_IRQS) {
                 seq_printf(p, "NMI: ");
-                for (j = 0; j < NR_CPUS; j++)
-                        if (cpu_online(j))
-                                seq_printf(p, "%10u ", nmi_count(j));
+                for_each_cpu(j)
+                        seq_printf(p, "%10u ", nmi_count(j));
                 seq_putc(p, '\n');
 #ifdef CONFIG_X86_LOCAL_APIC
                 seq_printf(p, "LOC: ");
-                for (j = 0; j < NR_CPUS; j++)
-                        if (cpu_online(j))
-                                seq_printf(p, "%10u ",
-                                        per_cpu(irq_stat,j).apic_timer_irqs);
+                for_each_cpu(j)
+                        seq_printf(p, "%10u ",
+                                per_cpu(irq_stat,j).apic_timer_irqs);
                 seq_putc(p, '\n');
 #endif
                 seq_printf(p, "ERR: %10u\n", atomic_read(&irq_err_count));
@@ -259,3 +258,45 @@ skip:
         }
         return 0;
 }
+
+#ifdef CONFIG_HOTPLUG_CPU
+#include <mach_apic.h>
+
+void fixup_irqs(cpumask_t map)
+{
+        unsigned int irq;
+        static int warned;
+
+        for (irq = 0; irq < NR_IRQS; irq++) {
+                cpumask_t mask;
+                if (irq == 2)
+                        continue;
+
+                cpus_and(mask, irq_affinity[irq], map);
+                if (any_online_cpu(mask) == NR_CPUS) {
+                        printk("Breaking affinity for irq %i\n", irq);
+                        mask = map;
+                }
+                if (irq_desc[irq].handler->set_affinity)
+                        irq_desc[irq].handler->set_affinity(irq, mask);
+                else if (irq_desc[irq].action && !(warned++))
+                        printk("Cannot set affinity for irq %i\n", irq);
+        }
+
+#if 0
+        barrier();
+        /* Ingo Molnar says: "after the IO-APIC masks have been redirected
+           [note the nop - the interrupt-enable boundary on x86 is two
+           instructions from sti] - to flush out pending hardirqs and
+           IPIs. After this point nothing is supposed to reach this CPU." */
+        __asm__ __volatile__("sti; nop; cli");
+        barrier();
+#else
+        /* That doesn't seem sufficient.  Give it 1ms. */
+        local_irq_enable();
+        mdelay(1);
+        local_irq_disable();
+#endif
+}
+#endif
+
diff --git a/arch/i386/kernel/process.c b/arch/i386/kernel/process.c
index aea2ce1145df..c1b11e8df60b 100644
--- a/arch/i386/kernel/process.c
+++ b/arch/i386/kernel/process.c
@@ -13,6 +13,7 @@
 
 #include <stdarg.h>
 
+#include <linux/cpu.h>
 #include <linux/errno.h>
 #include <linux/sched.h>
 #include <linux/fs.h>
@@ -55,6 +56,9 @@
 #include <linux/irq.h>
 #include <linux/err.h>
 
+#include <asm/tlbflush.h>
+#include <asm/cpu.h>
+
 asmlinkage void ret_from_fork(void) __asm__("ret_from_fork");
 
 static int hlt_counter;
@@ -143,14 +147,44 @@ static void poll_idle (void)
         }
 }
 
+#ifdef CONFIG_HOTPLUG_CPU
+#include <asm/nmi.h>
+/* We don't actually take CPU down, just spin without interrupts. */
+static inline void play_dead(void)
+{
+        /* Ack it */
+        __get_cpu_var(cpu_state) = CPU_DEAD;
+
+        /* We shouldn't have to disable interrupts while dead, but
+         * some interrupts just don't seem to go away, and this makes
+         * it "work" for testing purposes. */
+        /* Death loop */
+        while (__get_cpu_var(cpu_state) != CPU_UP_PREPARE)
+                cpu_relax();
+
+        local_irq_disable();
+        __flush_tlb_all();
+        cpu_set(smp_processor_id(), cpu_online_map);
+        enable_APIC_timer();
+        local_irq_enable();
+}
+#else
+static inline void play_dead(void)
+{
+        BUG();
+}
+#endif /* CONFIG_HOTPLUG_CPU */
+
 /*
  * The idle thread. There's no useful work to be
  * done, so just try to conserve power and have a
  * low exit latency (ie sit in a loop waiting for
  * somebody to say that they'd like to reschedule)
  */
-void cpu_idle (void)
+void cpu_idle(void)
 {
+        int cpu = raw_smp_processor_id();
+
         /* endless idle loop with no priority at all */
         while (1) {
                 while (!need_resched()) {
@@ -165,6 +199,9 @@ void cpu_idle (void)
                         if (!idle)
                                 idle = default_idle;
 
+                        if (cpu_is_offline(cpu))
+                                play_dead();
+
                         __get_cpu_var(irq_stat).idle_timestamp = jiffies;
                         idle();
                 }
diff --git a/arch/i386/kernel/smp.c b/arch/i386/kernel/smp.c
index 68be7d0c7238..35f521612b20 100644
--- a/arch/i386/kernel/smp.c
+++ b/arch/i386/kernel/smp.c
@@ -19,6 +19,7 @@
 #include <linux/mc146818rtc.h>
 #include <linux/cache.h>
 #include <linux/interrupt.h>
+#include <linux/cpu.h>
 #include <linux/module.h>
 
 #include <asm/mtrr.h>
@@ -164,7 +165,7 @@ void send_IPI_mask_bitmask(cpumask_t cpumask, int vector)
         unsigned long flags;
 
         local_irq_save(flags);
-                
+        WARN_ON(mask & ~cpus_addr(cpu_online_map)[0]);
         /*
          * Wait for idle.
          */
@@ -346,21 +347,21 @@ out:
 static void flush_tlb_others(cpumask_t cpumask, struct mm_struct *mm,
                                                 unsigned long va)
 {
-        cpumask_t tmp;
         /*
          * A couple of (to be removed) sanity checks:
          *
-         * - we do not send IPIs to not-yet booted CPUs.
          * - current CPU must not be in mask
          * - mask must exist :)
          */
         BUG_ON(cpus_empty(cpumask));
-
-        cpus_and(tmp, cpumask, cpu_online_map);
-        BUG_ON(!cpus_equal(cpumask, tmp));
         BUG_ON(cpu_isset(smp_processor_id(), cpumask));
         BUG_ON(!mm);
 
+        /* If a CPU which we ran on has gone down, OK. */
+        cpus_and(cpumask, cpumask, cpu_online_map);
+        if (cpus_empty(cpumask))
+                return;
+
         /*
          * i'm not happy about this global shared spinlock in the
          * MM hot path, but we'll see how contended it is.
@@ -476,6 +477,7 @@ void flush_tlb_all(void)
  */
 void smp_send_reschedule(int cpu)
 {
+        WARN_ON(cpu_is_offline(cpu));
         send_IPI_mask(cpumask_of_cpu(cpu), RESCHEDULE_VECTOR);
 }
 
@@ -516,10 +518,15 @@ int smp_call_function (void (*func) (void *info), void *info, int nonatomic,
  */
 {
         struct call_data_struct data;
-        int cpus = num_online_cpus()-1;
+        int cpus;
 
-        if (!cpus)
+        /* Holding any lock stops cpus from going down. */
+        spin_lock(&call_lock);
+        cpus = num_online_cpus() - 1;
+        if (!cpus) {
+                spin_unlock(&call_lock);
                 return 0;
+        }
 
         /* Can deadlock when called with interrupts disabled */
         WARN_ON(irqs_disabled());
@@ -531,7 +538,6 @@ int smp_call_function (void (*func) (void *info), void *info, int nonatomic,
         if (wait)
                 atomic_set(&data.finished, 0);
 
-        spin_lock(&call_lock);
         call_data = &data;
         mb();
         
diff --git a/arch/i386/kernel/smpboot.c b/arch/i386/kernel/smpboot.c
index c20d96d5c15c..ad74a46e9ef0 100644
--- a/arch/i386/kernel/smpboot.c
+++ b/arch/i386/kernel/smpboot.c
@@ -44,6 +44,9 @@
 #include <linux/smp_lock.h>
 #include <linux/irq.h>
 #include <linux/bootmem.h>
+#include <linux/notifier.h>
+#include <linux/cpu.h>
+#include <linux/percpu.h>
 
 #include <linux/delay.h>
 #include <linux/mc146818rtc.h>
@@ -96,6 +99,9 @@ static int trampoline_exec;
 
 static void map_cpu_to_logical_apicid(void);
 
+/* State of each CPU. */
+DEFINE_PER_CPU(int, cpu_state) = { 0 };
+
 /*
  * Currently trivial. Write the real->protected mode
  * bootstrap into the page concerned. The caller
@@ -1119,6 +1125,9 @@ static void __init smp_boot_cpus(unsigned int max_cpus)
    who understands all this stuff should rewrite it properly. --RR 15/Jul/02 */
 void __init smp_prepare_cpus(unsigned int max_cpus)
 {
+        smp_commenced_mask = cpumask_of_cpu(0);
+        cpu_callin_map = cpumask_of_cpu(0);
+        mb();
         smp_boot_cpus(max_cpus);
 }
 
@@ -1128,20 +1137,99 @@ void __devinit smp_prepare_boot_cpu(void)
         cpu_set(smp_processor_id(), cpu_callout_map);
 }
 
-int __devinit __cpu_up(unsigned int cpu)
+#ifdef CONFIG_HOTPLUG_CPU
+
+/* must be called with the cpucontrol mutex held */
+static int __devinit cpu_enable(unsigned int cpu)
 {
-        /* This only works at boot for x86.  See "rewrite" above. */
-        if (cpu_isset(cpu, smp_commenced_mask)) {
-                local_irq_enable();
-                return -ENOSYS;
+        /* get the target out of its holding state */
+        per_cpu(cpu_state, cpu) = CPU_UP_PREPARE;
+        wmb();
+
+        /* wait for the processor to ack it. timeout? */
+        while (!cpu_online(cpu))
+                cpu_relax();
+
+        fixup_irqs(cpu_online_map);
+        /* counter the disable in fixup_irqs() */
+        local_irq_enable();
+        return 0;
+}
+
+int __cpu_disable(void)
+{
+        cpumask_t map = cpu_online_map;
+        int cpu = smp_processor_id();
+
+        /*
+         * Perhaps use cpufreq to drop frequency, but that could go
+         * into generic code.
+         *
+         * We won't take down the boot processor on i386 due to some
+         * interrupts only being able to be serviced by the BSP.
+         * Especially so if we're not using an IOAPIC   -zwane
+         */
+        if (cpu == 0)
+                return -EBUSY;
+
+        /* We enable the timer again on the exit path of the death loop */
+        disable_APIC_timer();
+        /* Allow any queued timer interrupts to get serviced */
+        local_irq_enable();
+        mdelay(1);
+        local_irq_disable();
+
+        cpu_clear(cpu, map);
+        fixup_irqs(map);
+        /* It's now safe to remove this processor from the online map */
+        cpu_clear(cpu, cpu_online_map);
+        return 0;
+}
+
+void __cpu_die(unsigned int cpu)
+{
+        /* We don't do anything here: idle task is faking death itself. */
+        unsigned int i;
+
+        for (i = 0; i < 10; i++) {
+                /* They ack this in play_dead by setting CPU_DEAD */
+                if (per_cpu(cpu_state, cpu) == CPU_DEAD)
+                        return;
+                current->state = TASK_UNINTERRUPTIBLE;
+                schedule_timeout(HZ/10);
         }
+        printk(KERN_ERR "CPU %u didn't die...\n", cpu);
+}
+#else /* ... !CONFIG_HOTPLUG_CPU */
+int __cpu_disable(void)
+{
+        return -ENOSYS;
+}
 
+void __cpu_die(unsigned int cpu)
+{
+        /* We said "no" in __cpu_disable */
+        BUG();
+}
+#endif /* CONFIG_HOTPLUG_CPU */
+
+int __devinit __cpu_up(unsigned int cpu)
+{
         /* In case one didn't come up */
         if (!cpu_isset(cpu, cpu_callin_map)) {
+                printk(KERN_DEBUG "skipping cpu%d, didn't come online\n", cpu);
                 local_irq_enable();
                 return -EIO;
         }
 
+#ifdef CONFIG_HOTPLUG_CPU
+        /* Already up, and in cpu_quiescent now? */
+        if (cpu_isset(cpu, smp_commenced_mask)) {
+                cpu_enable(cpu);
+                return 0;
+        }
+#endif
+
         local_irq_enable();
         /* Unleash the CPU! */
         cpu_set(cpu, smp_commenced_mask);
diff --git a/arch/i386/kernel/traps.c b/arch/i386/kernel/traps.c
index e4d4e2162c7a..207ea8ba7169 100644
--- a/arch/i386/kernel/traps.c
+++ b/arch/i386/kernel/traps.c
@@ -625,6 +625,14 @@ fastcall void do_nmi(struct pt_regs * regs, long error_code)
         nmi_enter();
 
         cpu = smp_processor_id();
+
+#ifdef CONFIG_HOTPLUG_CPU
+        if (!cpu_online(cpu)) {
+                nmi_exit();
+                return;
+        }
+#endif
+
         ++nmi_count(cpu);
 
         if (!nmi_callback(regs, cpu))