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x86/smpboot: Unbreak CPU0 hotplug

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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: Vitaly 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: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Vitaly Kuznetsov 2017-08-03 12:58:18 +02:00 committed by Ingo Molnar
parent e93c17301a
commit 10e66760fa
1 changed files with 17 additions and 13 deletions
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30
arch/x86/kernel/smpboot.c
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@ -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;
}
/**