[PATCH 4/6] x86/smpboot: Split up native_cpu_up into separate phases

[David Woodhouse]

There are four logical parts to what native_cpu_up() does.

First it actually wakes AP.

Second, it waits for the AP to make it as far as wait_for_master_cpu()
which sets that CPU's bit in cpu_initialized_mask, and sets the bit in
cpu_callout_mask to let the AP proceed through cpu_init().

Then, it waits for the AP to finish cpu_init() and get as far as the
smp_callin() call, which sets that CPU's bit in cpu_callin_mask.

Finally, it does the TSC synchronization and waits for the AP to actually
mark itself online in cpu_online_mask.

This commit should have no behavioural change, but merely splits those
phases out into separate functions so that future commits and make them
happen in parallel for all APs.

Signed-off-by: David Woodhouse <dwmw@xxxxxxxxxxxx>
---
 arch/x86/kernel/smpboot.c | 136 +++++++++++++++++++++++---------------
 1 file changed, 82 insertions(+), 54 deletions(-)

diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c
index bec0059d3d3d..649b8236309b 100644
--- a/arch/x86/kernel/smpboot.c
+++ b/arch/x86/kernel/smpboot.c
@@ -1039,9 +1039,7 @@ static int do_boot_cpu(int apicid, int cpu, struct task_struct *idle,
 {
 	/* start_ip had better be page-aligned! */
 	unsigned long start_ip = real_mode_header->trampoline_start;
-
 	unsigned long boot_error = 0;
-	unsigned long timeout;
 
 	idle->thread.sp = (unsigned long)task_pt_regs(idle);
 	early_gdt_descr.address = (unsigned long)get_cpu_gdt_rw(cpu);
@@ -1094,55 +1092,70 @@ static int do_boot_cpu(int apicid, int cpu, struct task_struct *idle,
 		boot_error = wakeup_cpu_via_init_nmi(cpu, start_ip, apicid,
 						     cpu0_nmi_registered);
 
-	if (!boot_error) {
-		/*
-		 * Wait 10s total for first sign of life from AP
-		 */
-		boot_error = -1;
-		timeout = jiffies + 10*HZ;
-		while (time_before(jiffies, timeout)) {
-			if (cpumask_test_cpu(cpu, cpu_initialized_mask)) {
-				/*
-				 * Tell AP to proceed with initialization
-				 */
-				cpumask_set_cpu(cpu, cpu_callout_mask);
-				boot_error = 0;
-				break;
-			}
-			schedule();
-		}
-	}
+	return boot_error;
+}
 
-	if (!boot_error) {
-		/*
-		 * Wait till AP completes initial initialization
-		 */
-		while (!cpumask_test_cpu(cpu, cpu_callin_mask)) {
-			/*
-			 * Allow other tasks to run while we wait for the
-			 * AP to come online. This also gives a chance
-			 * for the MTRR work(triggered by the AP coming online)
-			 * to be completed in the stop machine context.
-			 */
-			schedule();
-		}
+static int do_wait_cpu_cpumask(unsigned int cpu, const struct cpumask *mask)
+{
+	unsigned long timeout;
+
+	/*
+	 * Wait up to 10s for the CPU to report in.
+	 */
+	timeout = jiffies + 10*HZ;
+	while (time_before(jiffies, timeout)) {
+		if (cpumask_test_cpu(cpu, mask))
+			return 0;
+
+		schedule();
 	}
+	return -1;
+}
 
-	if (x86_platform.legacy.warm_reset) {
-		/*
-		 * Cleanup possible dangling ends...
-		 */
-		smpboot_restore_warm_reset_vector();
+static int do_wait_cpu_initialized(unsigned int cpu)
+{
+	/*
+	 * Wait for first sign of life from AP.
+	 */
+	if (do_wait_cpu_cpumask(cpu, cpu_initialized_mask))
+		return -1;
+
+	cpumask_set_cpu(cpu, cpu_callout_mask);
+	return 0;
+}
+
+static int do_wait_cpu_callin(unsigned int cpu)
+{
+	/*
+	 * Wait till AP completes initial initialization.
+	 */
+	return do_wait_cpu_cpumask(cpu, cpu_callin_mask);
+}
+
+static int do_wait_cpu_online(unsigned int cpu)
+{
+	unsigned long flags;
+
+	/*
+	 * Check TSC synchronization with the AP (keep irqs disabled
+	 * while doing so):
+	 */
+	local_irq_save(flags);
+	check_tsc_sync_source(cpu);
+	local_irq_restore(flags);
+
+	while (!cpu_online(cpu)) {
+		cpu_relax();
+		touch_nmi_watchdog();
 	}
 
-	return boot_error;
+	return 0;
 }
 
-int native_cpu_up(unsigned int cpu, struct task_struct *tidle)
+int do_cpu_up(unsigned int cpu, struct task_struct *tidle)
 {
 	int apicid = apic->cpu_present_to_apicid(cpu);
 	int cpu0_nmi_registered = 0;
-	unsigned long flags;
 	int err, ret = 0;
 
 	lockdep_assert_irqs_enabled();
@@ -1189,19 +1202,6 @@ int native_cpu_up(unsigned int cpu, struct task_struct *tidle)
 		goto unreg_nmi;
 	}
 
-	/*
-	 * Check TSC synchronization with the AP (keep irqs disabled
-	 * while doing so):
-	 */
-	local_irq_save(flags);
-	check_tsc_sync_source(cpu);
-	local_irq_restore(flags);
-
-	while (!cpu_online(cpu)) {
-		cpu_relax();
-		touch_nmi_watchdog();
-	}
-
 unreg_nmi:
 	/*
 	 * Clean up the nmi handler. Do this after the callin and callout sync
@@ -1213,6 +1213,34 @@ int native_cpu_up(unsigned int cpu, struct task_struct *tidle)
 	return ret;
 }
 
+int native_cpu_up(unsigned int cpu, struct task_struct *tidle)
+{
+	int ret;
+
+	ret = do_cpu_up(cpu, tidle);
+	if (ret)
+		return ret;
+
+	ret = do_wait_cpu_initialized(cpu);
+	if (ret)
+		return ret;
+
+	ret = do_wait_cpu_callin(cpu);
+	if (ret)
+		return ret;
+
+	ret = do_wait_cpu_online(cpu);
+
+	if (x86_platform.legacy.warm_reset) {
+		/*
+		 * Cleanup possible dangling ends...
+		 */
+		smpboot_restore_warm_reset_vector();
+	}
+
+	return ret;
+}
+
 /**
  * arch_disable_smp_support() - disables SMP support for x86 at runtime
  */
-- 
2.29.2