On Mon, 2014-04-14 at 17:11 +0200, Igor Mammedov 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. Please also add description that the master CPU times out when an AP does not start initialization within 10 seconds. > Signed-off-by: Igor Mammedov <imammedo@xxxxxxxxxx> > --- > v2: > - ammend comment in cpu_init() > 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. > v4: > - move common code in cpu_init() for x32/x64 in shared > helper function wait_for_master_cpu() > - add WARN_ON(cpumask_test_and_set_cpu(cpu, cpu_initialized_mask)) > to wait_formaster_cpu() > --- > arch/x86/kernel/cpu/common.c | 27 +++++++----- > arch/x86/kernel/smpboot.c | 98 +++++++++++++----------------------------- > 2 files changed, 46 insertions(+), 79 deletions(-) > > diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c > index a135239..a4bcbac 100644 > --- a/arch/x86/kernel/cpu/common.c > +++ b/arch/x86/kernel/cpu/common.c > @@ -1221,6 +1221,17 @@ static void dbg_restore_debug_regs(void) > #define dbg_restore_debug_regs() > #endif /* ! CONFIG_KGDB */ > > +static void wait_for_master_cpu(int cpu) > +{ > + /* > + * 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(); > +} > + > /* > * cpu_init() initializes state that is per-CPU. Some data is already > * initialized (naturally) in the bootstrap process, such as the GDT > @@ -1236,16 +1247,17 @@ 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); > > @@ -1257,9 +1269,6 @@ 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); > @@ -1336,13 +1345,9 @@ 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 ae2fd97..44903ad 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 > @@ -750,8 +718,8 @@ 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(); > @@ -799,6 +767,14 @@ 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); I think smp_mb() should be added here to ensure that the target AP sees this change. > + > + /* > * Wake up a CPU in difference cases: > * - Use the method in the APIC driver if it's defined > * Otherwise, > @@ -810,55 +786,41 @@ 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(); > + } > + } When 10s passed, the master could set a new flag, ex. cpu_callout_error_mask, which wait_for_master_cpu() checks and call play_dead() when it is set. This avoids AP to spin forever when 10s becomes not long enough. But it does not have to be part of this patchset, though. > + if (!boot_error) { > /* > - * Wait 5s total for a response > + * Wait till AP completes initial initialization We should generally avoid such wait w/o a timeout condition, but since native_cpu_up() waits till cpu_online(cpu) anyway after this point, this seems OK... I wonder if we need touch_nmi_watchdog(), though. Thanks, -Toshi -- To unsubscribe from this list: send the line "unsubscribe linux-acpi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
