Re: [RFC v2] [x86]: abort secondary cpu bringup gracefully

[Igor Mammedov]

ping for reviewers.

Please review patch.

On 05/14/2012 01:09 PM, Igor Mammedov wrote:
> Forgot to cc v1 to tglx, so reposting fixed v2.
>
> Thomas,
>    is patch below what you've meant?
>
> Master cpu may timeout before cpu_callin_mask is set and decide to
> abort cpu boot but being onlined cpu will continue to boot, set
> cpu_active_mask and wait in check_tsc_sync_target() for master cpu
> to arrive, that will never happen because master cpu aborted boot
> proccess. Following attempt to online next cpu will hang in
> stop_machine because it will wait on comletion of stop_work on all
> cpus from cpu_active_mask and that will never happen because first
> failed cpu spins in check_tsc_sync_target().
>
> Introduce cpu_may_complete_boot_mask which will be set by master cpu
> if it goes via normal boot path and decides to continue cpu bring up.
> Being onlined cpu will continue to boot only if master cpu confirms
> via cpu_may_complete_boot_mask its intention not to abort cpu bring up.
> Otherwise being onlined cpu will gracefully die.
>
> Reason for moving setting cpu_callin_mask before is that one of
> CPU_STARTING notfiers sets cpu_active_mask before it is known for sure
> that cpu may continue to boot. And that may lead to soft lookups in
> stop_machine when next cpu is booted but failed one haven't completed
> cpu_*_mask cleaups yet.
>
> It's ok for being onlined cpu to set cpu_callin_mask before calling
> CPU_STARTING notifiers because master cpu may first wait on being
> booted cpu in check_tsc_sync_source() and after that it waits in
> native_cpu_up() till being booted cpu comes online and only when
> being booted cpu sets cpu_online_mask it will exit native_cpu_up()
> and then call CPU_ONLINE notifiers. So call sequence looks like this:
>
>      CPU1                            CPU2
>
>    wait till CPU2 sets
>    cpu_callin_mask
>   -------------------------------------------------
>                                      set cpu_callin_mask
>                                      wait till CPU1 sets
>                                      cpu_may_complete_boot_mask
>   -------------------------------------------------
>    got ack from CPU2 via
>    cpu_callin_mask
>
>    set cpu_may_complete_boot_mask
>    exit do_boot_cpu and return into
>    native_cpu_up()
>
>    in native_cpu_up() CPU1 may spin first in
>    check_tsc_sync_source()
>    and then wait till CPU2 will set
>    cpu_online_mask:
>
>          while (!cpu_online(cpu)) {
>                  cpu_relax();
>                  touch_nmi_watchdog();
>          }
>   -------------------------------------------------
>                                       got ack from CPU1 via
>                                       cpu_may_complete_boot_mask
>
>                                       call CPU_STARTING notifiers
>                                       ...
>                                       call check_tsc_sync_target()
>                                       set cpu_online_mask
>   -------------------------------------------------
>    got ack from CPU2 that it
>    is online, return from native_cpu_up()
>
>    call CPU_ONLINE notifiers
>   ----
>
> In addition if being onlined cpu timed-out waiting on cpu_callout_mask,
> it should not panic but rather die.
>
> v2:
>    - added missing remove_siblinginfo() on 'die' error path.
>    - added explanation why it's ok to set cpu_callin_mask before calling
>      CPU_STARTING notifiers
>
> Signed-off-by: Igor Mammedov<imammedo@xxxxxxxxxx>
> ---
>   arch/x86/include/asm/cpumask.h |    1 +
>   arch/x86/kernel/cpu/common.c   |    2 ++
>   arch/x86/kernel/smpboot.c      |   39 ++++++++++++++++++++++++++++++++++++---
>   3 files changed, 39 insertions(+), 3 deletions(-)
>
> diff --git a/arch/x86/include/asm/cpumask.h b/arch/x86/include/asm/cpumask.h
> index 61c852f..eacd269 100644
> --- a/arch/x86/include/asm/cpumask.h
> +++ b/arch/x86/include/asm/cpumask.h
> @@ -7,6 +7,7 @@ extern cpumask_var_t cpu_callin_mask;
>   extern cpumask_var_t cpu_callout_mask;
>   extern cpumask_var_t cpu_initialized_mask;
>   extern cpumask_var_t cpu_sibling_setup_mask;
> +extern cpumask_var_t cpu_may_complete_boot_mask;
>
>   extern void setup_cpu_local_masks(void);
>
> diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
> index cf79302..50e91cb 100644
> --- a/arch/x86/kernel/cpu/common.c
> +++ b/arch/x86/kernel/cpu/common.c
> @@ -48,6 +48,7 @@
>   cpumask_var_t cpu_initialized_mask;
>   cpumask_var_t cpu_callout_mask;
>   cpumask_var_t cpu_callin_mask;
> +cpumask_var_t cpu_may_complete_boot_mask;
>
>   /* representing cpus for which sibling maps can be computed */
>   cpumask_var_t cpu_sibling_setup_mask;
> @@ -59,6 +60,7 @@ void __init setup_cpu_local_masks(void)
>   	alloc_bootmem_cpumask_var(&cpu_callin_mask);
>   	alloc_bootmem_cpumask_var(&cpu_callout_mask);
>   	alloc_bootmem_cpumask_var(&cpu_sibling_setup_mask);
> +	alloc_bootmem_cpumask_var(&cpu_may_complete_boot_mask);
>   }
>
>   static void __cpuinit default_init(struct cpuinfo_x86 *c)
> diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c
> index 6e1e406..b419e2e 100644
> --- a/arch/x86/kernel/smpboot.c
> +++ b/arch/x86/kernel/smpboot.c
> @@ -136,6 +136,10 @@ EXPORT_PER_CPU_SYMBOL(cpu_info);
>
>   atomic_t init_deasserted;
>
> +#ifdef CONFIG_HOTPLUG_CPU
> +static void remove_siblinginfo(int cpu);
> +#endif
> +
>   /*
>    * Report back to the Boot Processor.
>    * Running on AP.
> @@ -187,8 +191,9 @@ static void __cpuinit smp_callin(void)
>   	}
>
>   	if (!time_before(jiffies, timeout)) {
> -		panic("%s: CPU%d started up but did not get a callout!\n",
> +		pr_debug("%s: CPU%d started up but did not get a callout!\n",
>   		      __func__, cpuid);
> +		goto die;
>   	}
>
>   	/*
> @@ -232,12 +237,37 @@ static void __cpuinit smp_callin(void)
>   	set_cpu_sibling_map(raw_smp_processor_id());
>   	wmb();
>
> -	notify_cpu_starting(cpuid);
> -
>   	/*
>   	 * Allow the master to continue.
>   	 */
>   	cpumask_set_cpu(cpuid, cpu_callin_mask);
> +
> +	/*
> +	 * Wait for master to continue.
> +	 */
> +	for (timeout = 0; timeout<  50000; timeout++) {
> +		if (cpumask_test_cpu(cpuid, cpu_may_complete_boot_mask))
> +			break;
> +
> +		if (!cpumask_test_cpu(cpuid, cpu_callout_mask))
> +			break;
> +
> +		udelay(100);
> +	}
> +
> +	if (!cpumask_test_cpu(cpuid, cpu_may_complete_boot_mask))
> +		goto die;
> +
> +	notify_cpu_starting(cpuid);
> +	return;
> +
> +die:
> +	/* was set by cpu_init() */
> +	cpumask_clear_cpu(smp_processor_id(), cpu_initialized_mask);
> +	remove_siblinginfo(cpuid);
> +	cpumask_clear_cpu(smp_processor_id(), cpu_callin_mask);
> +	clear_local_APIC();
> +	play_dead();
>   }
>
>   /*
> @@ -774,6 +804,8 @@ do_rest:
>   		}
>
>   		if (cpumask_test_cpu(cpu, cpu_callin_mask)) {
> +			/* Signal AP that it may continue to boot */
> +			cpumask_set_cpu(cpu, cpu_may_complete_boot_mask);
>   			print_cpu_msr(&cpu_data(cpu));
>   			pr_debug("CPU%d: has booted.\n", cpu);
>   		} else {
> @@ -1250,6 +1282,7 @@ static void __ref remove_cpu_from_maps(int cpu)
>   	cpumask_clear_cpu(cpu, cpu_callin_mask);
>   	/* was set by cpu_init() */
>   	cpumask_clear_cpu(cpu, cpu_initialized_mask);
> +	cpumask_clear_cpu(cpu, cpu_may_complete_boot_mask);
>   	numa_remove_cpu(cpu);
>   }

--
-----
 Igor
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