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Commit 10e66760 authored by Vitaly Kuznetsov's avatar Vitaly Kuznetsov Committed by Ingo Molnar
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x86/smpboot: Unbreak CPU0 hotplug 



A hang on CPU0 onlining after a preceding offlining is observed. Trace
shows that CPU0 is stuck in check_tsc_sync_target() waiting for source
CPU to run check_tsc_sync_source() but this never happens. Source CPU,
in its turn, is stuck on synchronize_sched() which is called from
native_cpu_up() -> do_boot_cpu() -> unregister_nmi_handler().

So it's a classic ABBA deadlock, due to the use of synchronize_sched() in
unregister_nmi_handler().

Fix the bug by moving unregister_nmi_handler() from do_boot_cpu() to
native_cpu_up() after cpu onlining is done.

Signed-off-by: default avatarVitaly Kuznetsov <vkuznets@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20170803105818.9934-1-vkuznets@redhat.com


Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
parent e93c1730

arch/x86/kernel/smpboot.c

+17 −13
Original line number Diff line number Diff line
@@ -971,7 +971,8 @@ void common_cpu_up(unsigned int cpu, struct task_struct *idle) 
 * Returns zero if CPU booted OK, else error code from

 * ->wakeup_secondary_cpu.

 */

static int do_boot_cpu(int apicid, int cpu, struct task_struct *idle)

static int do_boot_cpu(int apicid, int cpu, struct task_struct *idle,

		       int *cpu0_nmi_registered)

{

	volatile u32 *trampoline_status =

		(volatile u32 *) __va(real_mode_header->trampoline_status);
@@ -979,7 +980,6 @@ static int do_boot_cpu(int apicid, int cpu, struct task_struct *idle) 
	unsigned long start_ip = real_mode_header->trampoline_start;



	unsigned long boot_error = 0;

	int cpu0_nmi_registered = 0;

	unsigned long timeout;



	idle->thread.sp = (unsigned long)task_pt_regs(idle);
@@ -1035,7 +1035,7 @@ static int do_boot_cpu(int apicid, int cpu, struct task_struct *idle) 
		boot_error = apic->wakeup_secondary_cpu(apicid, start_ip);

	else

		boot_error = wakeup_cpu_via_init_nmi(cpu, start_ip, apicid,

						     &cpu0_nmi_registered);

						     cpu0_nmi_registered);



	if (!boot_error) {

		/*
@@ -1080,12 +1080,6 @@ static int do_boot_cpu(int apicid, int cpu, struct task_struct *idle) 
		 */

		smpboot_restore_warm_reset_vector();

	}

	/*

	 * Clean up the nmi handler. Do this after the callin and callout sync

	 * to avoid impact of possible long unregister time.

	 */

	if (cpu0_nmi_registered)

		unregister_nmi_handler(NMI_LOCAL, "wake_cpu0");



	return boot_error;

}
@@ -1093,8 +1087,9 @@ static int do_boot_cpu(int apicid, int cpu, struct task_struct *idle) 
int native_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;

	int err, ret = 0;



	WARN_ON(irqs_disabled());
@@ -1131,10 +1126,11 @@ int native_cpu_up(unsigned int cpu, struct task_struct *tidle) 


	common_cpu_up(cpu, tidle);



	err = do_boot_cpu(apicid, cpu, tidle);

	err = do_boot_cpu(apicid, cpu, tidle, &cpu0_nmi_registered);

	if (err) {

		pr_err("do_boot_cpu failed(%d) to wakeup CPU#%u\n", err, cpu);

		return -EIO;

		ret = -EIO;

		goto unreg_nmi;

	}



	/*
@@ -1150,7 +1146,15 @@ int native_cpu_up(unsigned int cpu, struct task_struct *tidle) 
		touch_nmi_watchdog();

	}



	return 0;

unreg_nmi:

	/*

	 * Clean up the nmi handler. Do this after the callin and callout sync

	 * to avoid impact of possible long unregister time.

	 */

	if (cpu0_nmi_registered)

		unregister_nmi_handler(NMI_LOCAL, "wake_cpu0");



	return ret;

}



/**