On Thu, 01 May 2014 17:11:56 -0600 Toshi Kani <toshi.k...@hp.com> wrote:
> 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. added > > > Signed-off-by: Igor Mammedov <imamm...@redhat.com> > > --- > > 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. ok > > > + > > + /* > > * 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. I'm reluctant to add another to already too many cpu_*_mask, maybe we could reuse cpu_initialized_mask by clearing it on timeout. This way AP spinning on cpu_callout_mask could notice it and halt itself. It would be better to make it separate patch on top of this series, to reduce delay of bugfixes in this series. > > > + 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 If we don't wait here and fall through into tight loop waiting on cpu_online(cpu) in native_cpu_up() or check_tsc_sync_source() then stop_task for syncing MTTRs initiated from AP won't have a chance to run on the master CPU. > seems OK... I wonder if we need touch_nmi_watchdog(), though. There wasn't any touch_nmi_watchdog() in the original code and I don't think we need it here since we are not just spinning on CPU but giving control back to kernel calling schedule(), which would allow watchdog_task to do the job if needed. > Thanks, > -Toshi > > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
