Commit d04f41e3 authored by Ingo Molnar's avatar Ingo Molnar Committed by Linus Torvalds
Browse files

[PATCH] CPU hotplug: call check_tsc_sync_source() with irqs off 



check_tsc_sync_source() depends on being called with irqs disabled (it
checks whether the TSC is coherent across two specific CPUs). This is
incidentally true during bootup, but not during cpu hotplug __cpu_up().
This got found via smp_processor_id() debugging.

disable irqs explicitly and remove the unconditional enabling of
interrupts. Add touch_nmi_watchdog() to the cpu_online_map busy loop.

this bug is present both on i386 and on x86_64.

Reported-by: default avatarMichal Piotrowski <michal.k.k.piotrowski@gmail.com>
Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 08e15e81

arch/i386/kernel/smpboot.c

+10 −6
Original line number Diff line number Diff line
@@ -45,6 +45,7 @@ 
#include <linux/notifier.h>

#include <linux/cpu.h>

#include <linux/percpu.h>

#include <linux/nmi.h>



#include <linux/delay.h>

#include <linux/mc146818rtc.h>
@@ -1278,6 +1279,7 @@ void __cpu_die(unsigned int cpu) 


int __cpuinit __cpu_up(unsigned int cpu)

{

	unsigned long flags;

#ifdef CONFIG_HOTPLUG_CPU

	int ret = 0;
@@ -1297,23 +1299,25 @@ int __cpuinit __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;

	}



	local_irq_enable();



	per_cpu(cpu_state, cpu) = CPU_UP_PREPARE;

	/* Unleash the CPU! */

	cpu_set(cpu, smp_commenced_mask);



	/*

	 * Check TSC synchronization with the AP:

	 * 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_isset(cpu, cpu_online_map))

	while (!cpu_isset(cpu, cpu_online_map)) {

		cpu_relax();

		touch_nmi_watchdog();

	}



#ifdef CONFIG_X86_GENERICARCH

	if (num_online_cpus() > 8 && genapic == &apic_default)

arch/x86_64/kernel/smpboot.c

+4 −1
Original line number Diff line number Diff line
@@ -923,8 +923,9 @@ void __init smp_prepare_boot_cpu(void) 
 */

int __cpuinit __cpu_up(unsigned int cpu)

{

	int err;

	int apicid = cpu_present_to_apicid(cpu);

	unsigned long flags;

	int err;



	WARN_ON(irqs_disabled());
@@ -958,7 +959,9 @@ int __cpuinit __cpu_up(unsigned int cpu) 
	/*

  	 * Make sure and check TSC sync:

 	 */

	local_irq_save(flags);

	check_tsc_sync_source(cpu);

	local_irq_restore(flags);



	while (!cpu_isset(cpu, cpu_online_map))

		cpu_relax();

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