| Message ID | 1397488277-14865-6-git-send-email-imammedo@redhat.com (mailing list archive) |
|---|---|
| State | Not Applicable, archived |
| Headers | show |
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@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. > + > + /* > * 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@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On Thu, 01 May 2014 17:11:56 -0600 Toshi Kani <toshi.kani@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 <imammedo@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-acpi" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On Fri, 2014-05-02 at 10:21 +0200, Igor Mammedov wrote: > On Thu, 01 May 2014 17:11:56 -0600 > Toshi Kani <toshi.kani@hp.com> wrote: : > > 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. I agree that there are too many cpu_* masks. IMHO, these cpu rendezvous masks, initialized/callout/callin, should be combined into a per-cpu flag. There is not much point of being individual masks. Anyway, I do not think cpu_initialized_mask can be reused here. > It would be better to make it separate patch on top of this series, > to reduce delay of bugfixes in this series. Agreed. > > > > > + 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. Agreed. Thanks, -Toshi -- To unsubscribe from this list: send the line "unsubscribe linux-acpi" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On Fri, 02 May 2014 08:52:22 -0600 Toshi Kani <toshi.kani@hp.com> wrote: > On Fri, 2014-05-02 at 10:21 +0200, Igor Mammedov wrote: > > On Thu, 01 May 2014 17:11:56 -0600 > > Toshi Kani <toshi.kani@hp.com> wrote: > : > > > 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. > > I agree that there are too many cpu_* masks. IMHO, these cpu rendezvous > masks, initialized/callout/callin, should be combined into a per-cpu > flag. There is not much point of being individual masks. > > Anyway, I do not think cpu_initialized_mask can be reused here. I'll look if we could use percpu here when writing patch to halt timed-out AP. > > > It would be better to make it separate patch on top of this series, > > to reduce delay of bugfixes in this series. > > Agreed. > > > > > > > > + 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. > > Agreed. > > Thanks, > -Toshi >
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); + + /* * 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(); + } + } + 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 */
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. Signed-off-by: Igor Mammedov <imammedo@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(-)