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Message-ID: <20140702112639.1977facb@thinkpad>
Date: Wed, 2 Jul 2014 11:26:39 +0200
From: Igor Mammedov <imammedo@...hat.com>
To: linux-kernel@...r.kernel.org
Cc: mingo@...hat.com, hpa@...or.com
Subject: Re: [PATCH v7] x86: initialize secondary CPU only if master CPU
will wait for it
On Fri, 20 Jun 2014 14:23:11 +0200
Igor Mammedov <imammedo@...hat.com> wrote:
> Hang is observed on virtual machines during CPU hotplug,
> especially in big guests with many CPUs. (It reproducible
> more often if host is over-committed).
>
> It happens because master CPU gives up waiting on
> secondary CPU and allows it to run wild. As result
> AP causes locking or crashing system. For example
> as described here: https://lkml.org/lkml/2014/3/6/257
>
> If master CPU have sent STARTUP IPI successfully,
> and AP signalled to master CPU that it's ready
> to start initialization, make master CPU wait
> indefinitely till AP is onlined.
> To ensure that AP won't ever run wild, make it
> wait at early startup till master CPU confirms its
> intention to wait for AP. If AP doesn't respond in 10
> seconds, the master CPU will timeout and cancel
> AP onlining.
>
> Signed-off-by: Igor Mammedov <imammedo@...hat.com>
ping,
may be it's better to take in for the next merge window
> ---
> v7:
> - fix stuck boot with non SMP config
> - fix stuck paravirtual Xen SMP boot with more than 1VCPU
> and CPU hotplug
> v6:
> - no changes
> v5:
> - add smp_mb() after clearing cpu_initialized_mask in do_boot_cpu()
> - add 10 sec timeout description into commit message.
> v4:
> - move commont code in cpu_init() for x32/x64 in shared
> helper function wait_formaster_cpu()
> - add WARN_ON(cpumask_test_and_set_cpu(cpu, cpu_initialized_mask))
> to wait_formaster_cpu()
> v3:
> - leave timeouts in do_boot_cpu(), so that master CPU
> won't hang if AP doesn't respond, use cpu_initialized_mask
> as a way for AP to signal to master CPU that it's ready
> to start initialzation.
> v2:
> - ammend comment in cpu_init()
> ---
> arch/x86/kernel/cpu/common.c | 29 ++++++++-----
> arch/x86/kernel/smpboot.c | 99 +++++++++++++-----------------------------
> arch/x86/xen/smp.c | 2 +
> 3 files changed, 51 insertions(+), 79 deletions(-)
>
> diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
> index ef1b93f..0b94e57 100644
> --- a/arch/x86/kernel/cpu/common.c
> +++ b/arch/x86/kernel/cpu/common.c
> @@ -1258,6 +1258,19 @@ static void dbg_restore_debug_regs(void)
> #define dbg_restore_debug_regs()
> #endif /* ! CONFIG_KGDB */
>
> +static void wait_for_master_cpu(int cpu)
> +{
> +#ifdef CONFIG_SMP
> + /*
> + * wait for ACK from master CPU before continuing
> + * with AP initialization
> + */
> + WARN_ON(cpumask_test_and_set_cpu(cpu, cpu_initialized_mask));
> + while (!cpumask_test_cpu(cpu, cpu_callout_mask))
> + cpu_relax();
> +#endif
> +}
> +
> /*
> * cpu_init() initializes state that is per-CPU. Some data is already
> * initialized (naturally) in the bootstrap process, such as the GDT
> @@ -1273,16 +1286,17 @@ void cpu_init(void)
> struct task_struct *me;
> struct tss_struct *t;
> unsigned long v;
> - int cpu;
> + int cpu = stack_smp_processor_id();
> int i;
>
> + wait_for_master_cpu(cpu);
> +
> /*
> * Load microcode on this cpu if a valid microcode is available.
> * This is early microcode loading procedure.
> */
> load_ucode_ap();
>
> - cpu = stack_smp_processor_id();
> t = &per_cpu(init_tss, cpu);
> oist = &per_cpu(orig_ist, cpu);
>
> @@ -1294,9 +1308,6 @@ void cpu_init(void)
>
> me = current;
>
> - if (cpumask_test_and_set_cpu(cpu, cpu_initialized_mask))
> - panic("CPU#%d already initialized!\n", cpu);
> -
> pr_debug("Initializing CPU#%d\n", cpu);
>
> clear_in_cr4(X86_CR4_VME|X86_CR4_PVI|X86_CR4_TSD|X86_CR4_DE);
> @@ -1373,13 +1384,9 @@ void cpu_init(void)
> struct tss_struct *t = &per_cpu(init_tss, cpu);
> struct thread_struct *thread = &curr->thread;
>
> - show_ucode_info_early();
> + wait_for_master_cpu(cpu);
>
> - if (cpumask_test_and_set_cpu(cpu, cpu_initialized_mask)) {
> - printk(KERN_WARNING "CPU#%d already initialized!\n", cpu);
> - for (;;)
> - local_irq_enable();
> - }
> + show_ucode_info_early();
>
> printk(KERN_INFO "Initializing CPU#%d\n", cpu);
>
> diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c
> index 5492798..a1472b7 100644
> --- a/arch/x86/kernel/smpboot.c
> +++ b/arch/x86/kernel/smpboot.c
> @@ -111,7 +111,6 @@ atomic_t init_deasserted;
> static void smp_callin(void)
> {
> int cpuid, phys_id;
> - unsigned long timeout;
>
> /*
> * If waken up by an INIT in an 82489DX configuration
> @@ -130,37 +129,6 @@ static void smp_callin(void)
> * (This works even if the APIC is not enabled.)
> */
> phys_id = read_apic_id();
> - if (cpumask_test_cpu(cpuid, cpu_callin_mask)) {
> - panic("%s: phys CPU#%d, CPU#%d already present??\n", __func__,
> - phys_id, cpuid);
> - }
> - pr_debug("CPU#%d (phys ID: %d) waiting for CALLOUT\n", cpuid, phys_id);
> -
> - /*
> - * STARTUP IPIs are fragile beasts as they might sometimes
> - * trigger some glue motherboard logic. Complete APIC bus
> - * silence for 1 second, this overestimates the time the
> - * boot CPU is spending to send the up to 2 STARTUP IPIs
> - * by a factor of two. This should be enough.
> - */
> -
> - /*
> - * Waiting 2s total for startup (udelay is not yet working)
> - */
> - timeout = jiffies + 2*HZ;
> - while (time_before(jiffies, timeout)) {
> - /*
> - * Has the boot CPU finished it's STARTUP sequence?
> - */
> - if (cpumask_test_cpu(cpuid, cpu_callout_mask))
> - break;
> - cpu_relax();
> - }
> -
> - if (!time_before(jiffies, timeout)) {
> - panic("%s: CPU%d started up but did not get a callout!\n",
> - __func__, cpuid);
> - }
>
> /*
> * the boot CPU has finished the init stage and is spinning
> @@ -757,8 +725,8 @@ 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 timeout;
> int cpu0_nmi_registered = 0;
> + unsigned long timeout;
>
> /* Just in case we booted with a single CPU. */
> alternatives_enable_smp();
> @@ -806,6 +774,15 @@ static int do_boot_cpu(int apicid, int cpu, struct task_struct *idle)
> }
>
> /*
> + * AP might wait on cpu_callout_mask in cpu_init() with
> + * cpu_initialized_mask set if previous attempt to online
> + * it timed-out. Clear cpu_initialized_mask so that after
> + * INIT/SIPI it could start with a clean state.
> + */
> + cpumask_clear_cpu(cpu, cpu_initialized_mask);
> + smp_mb();
> +
> + /*
> * Wake up a CPU in difference cases:
> * - Use the method in the APIC driver if it's defined
> * Otherwise,
> @@ -817,55 +794,41 @@ 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) {
> /*
> - * allow APs to start initializing.
> + * Wait 10s total for a response from AP
> */
> - pr_debug("Before Callout %d\n", cpu);
> - cpumask_set_cpu(cpu, cpu_callout_mask);
> - pr_debug("After Callout %d\n", cpu);
> + 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;
> + }
> + udelay(100);
> + schedule();
> + }
> + }
>
> + if (!boot_error) {
> /*
> - * Wait 5s total for a response
> + * Wait till AP completes initial initialization
> */
> - for (timeout = 0; timeout < 50000; timeout++) {
> - if (cpumask_test_cpu(cpu, cpu_callin_mask))
> - break; /* It has booted */
> - udelay(100);
> + 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.
> */
> + udelay(100);
> schedule();
> }
> -
> - if (cpumask_test_cpu(cpu, cpu_callin_mask)) {
> - print_cpu_msr(&cpu_data(cpu));
> - pr_debug("CPU%d: has booted.\n", cpu);
> - } else {
> - boot_error = 1;
> - if (*trampoline_status == 0xA5A5A5A5)
> - /* trampoline started but...? */
> - pr_err("CPU%d: Stuck ??\n", cpu);
> - else
> - /* trampoline code not run */
> - pr_err("CPU%d: Not responding\n", cpu);
> - if (apic->inquire_remote_apic)
> - apic->inquire_remote_apic(apicid);
> - }
> - }
> -
> - if (boot_error) {
> - /* Try to put things back the way they were before ... */
> - numa_remove_cpu(cpu); /* was set by numa_add_cpu */
> -
> - /* was set by do_boot_cpu() */
> - cpumask_clear_cpu(cpu, cpu_callout_mask);
> -
> - /* was set by cpu_init() */
> - cpumask_clear_cpu(cpu, cpu_initialized_mask);
> }
>
> /* mark "stuck" area as not stuck */
> diff --git a/arch/x86/xen/smp.c b/arch/x86/xen/smp.c
> index 7005974..3631e71 100644
> --- a/arch/x86/xen/smp.c
> +++ b/arch/x86/xen/smp.c
> @@ -360,6 +360,8 @@ cpu_initialize_context(unsigned int cpu, struct task_struct *idle)
> struct desc_struct *gdt;
> unsigned long gdt_mfn;
>
> + /* used to tell cpu_init() that it can proceed with initialization */
> + cpumask_set_cpu(cpu, cpu_callout_mask);
> if (cpumask_test_and_set_cpu(cpu, xen_cpu_initialized_map))
> return 0;
>
> --
> 1.7.1
>
> --
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>
--
Regards,
Igor
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