Re: [PATCH tip/core/rcu 02/20] x86: Use common outgoing-CPU-notification code

["Paul E. McKenney" <paulmck@linux.vnet.ibm.com>]

On Thu, Mar 05, 2015 at 04:17:59PM -0500, Boris Ostrovsky wrote:
> On 03/04/2015 10:25 AM, Paul E. McKenney wrote:
> >On Wed, Mar 04, 2015 at 09:55:11AM -0500, Boris Ostrovsky wrote:
> 
> >>The simple solution is to stop calling native_cpu_die() above but
> >>I'd like to use common code in native_cpu_die(). I'll see if I can
> >>carve it out without too much damage to x86.
> >
> >Very good, thank you!  I look forward to seeing your patch.
> 
> How about something like this, on top of your original 02/20 patch
> (this is copy-paste but hopefully it can be applied):

Unfortunately, no joy.  :-(

I was able to fix a couple of whitespace problems, but it still didn't
like this hunk: "@@ -766,12 +778,6 @@".

Could you please send the patch as an attachment, post it on the web
somewhere, or otherwise get me a clean copy it it?

							Thanx, Paul

>  arch/x86/include/asm/smp.h |    1 +
>  arch/x86/kernel/smpboot.c  |   12 +++++++++++-
>  arch/x86/xen/smp.c         |   34 ++++++++++++++++++++--------------
>  3 files changed, 32 insertions(+), 15 deletions(-)
> 
> diff --git a/arch/x86/include/asm/smp.h b/arch/x86/include/asm/smp.h
> index 8cd27e0..a5cb4f6 100644
> --- a/arch/x86/include/asm/smp.h
> +++ b/arch/x86/include/asm/smp.h
> @@ -155,6 +155,7 @@ void native_smp_prepare_cpus(unsigned int max_cpus);
>  void native_smp_cpus_done(unsigned int max_cpus);
>  int native_cpu_up(unsigned int cpunum, struct task_struct *tidle);
>  int native_cpu_disable(void);
> +int common_cpu_die(unsigned int cpu);
>  void native_cpu_die(unsigned int cpu);
>  void native_play_dead(void);
>  void play_dead_common(void);
> diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c
> index ff24fbd..c8fa349 100644
> --- a/arch/x86/kernel/smpboot.c
> +++ b/arch/x86/kernel/smpboot.c
> @@ -1345,8 +1345,10 @@ int native_cpu_disable(void)
>  	return 0;
>  }
> 
> -void native_cpu_die(unsigned int cpu)
> +int common_cpu_die(unsigned int cpu)
>  {
> +	int ret = 0;
> +
>  	/* We don't do anything here: idle task is faking death itself. */
> 
>  	/* They ack this in play_dead() by setting CPU_DEAD */
> @@ -1355,7 +1357,15 @@ void native_cpu_die(unsigned int cpu)
>  			pr_info("CPU %u is now offline\n", cpu);
>  	} else {
>  		pr_err("CPU %u didn't die...\n", cpu);
> +		ret = -1;
>  	}
> +
> +	return ret;
> +}
> +
> +void native_cpu_die(unsigned int cpu)
> +{
> +	common_cpu_die(cpu);
>  }
> 
>  void play_dead_common(void)
> diff --git a/arch/x86/xen/smp.c b/arch/x86/xen/smp.c
> index e2c7389..1c5e760 100644
> --- a/arch/x86/xen/smp.c
> +++ b/arch/x86/xen/smp.c
> @@ -455,7 +455,10 @@ static int xen_cpu_up(unsigned int cpu, struct
> task_struct *idle)
>  	xen_setup_timer(cpu);
>  	xen_init_lock_cpu(cpu);
> 
> -	/* Xen outgoing CPUs need help cleaning up, so -EBUSY is an error. */
> +	/*
> +	 * PV VCPUs are always successfully taken down (see 'while' loop
> +	 * in xen_cpu_die()), so -EBUSY is an error.
> +	 */
>  	rc = cpu_check_up_prepare(cpu);
>  	if (rc)
>  		return rc;
> @@ -508,12 +511,11 @@ static void xen_cpu_die(unsigned int cpu)
>  		schedule_timeout(HZ/10);
>  	}
> 
> -	(void)cpu_wait_death(cpu, 5);
> -	/* FIXME: Are the below calls really safe in case of timeout? */
> -
> -	xen_smp_intr_free(cpu);
> -	xen_uninit_lock_cpu(cpu);
> -	xen_teardown_timer(cpu);
> +	if (common_cpu_die(cpu) == 0) {
> +		xen_smp_intr_free(cpu);
> +		xen_uninit_lock_cpu(cpu);
> +		xen_teardown_timer(cpu);
> +	}
>  }
> 
>  static void xen_play_dead(void) /* used only with HOTPLUG_CPU */
> @@ -745,6 +747,16 @@ static void __init
> xen_hvm_smp_prepare_cpus(unsigned int max_cpus)
>  static int xen_hvm_cpu_up(unsigned int cpu, struct task_struct *tidle)
>  {
>  	int rc;
> +
> +	/*
> +	 * This can happen if CPU was offlined earlier and
> +	 * offlining timed out in common_cpu_die().
> +	 */
> +	if (cpu_report_state(cpu) == CPU_DEAD_FROZEN) {
> +		xen_smp_intr_free(cpu);
> +		xen_uninit_lock_cpu(cpu);
> +	}
> +
>  	/*
>  	 * xen_smp_intr_init() needs to run before native_cpu_up()
>  	 * so that IPI vectors are set up on the booting CPU before
> @@ -766,12 +778,6 @@ static int xen_hvm_cpu_up(unsigned int cpu,
> struct task_struct *tidle)
>  	return rc;
>  }
> 
> -static void xen_hvm_cpu_die(unsigned int cpu)
> -{
> -	xen_cpu_die(cpu);
> -	native_cpu_die(cpu);
> -}
> -
>  void __init xen_hvm_smp_init(void)
>  {
>  	if (!xen_have_vector_callback)
> @@ -779,7 +785,7 @@ void __init xen_hvm_smp_init(void)
>  	smp_ops.smp_prepare_cpus = xen_hvm_smp_prepare_cpus;
>  	smp_ops.smp_send_reschedule = xen_smp_send_reschedule;
>  	smp_ops.cpu_up = xen_hvm_cpu_up;
> -	smp_ops.cpu_die = xen_hvm_cpu_die;
> +	smp_ops.cpu_die = xen_cpu_die;
>  	smp_ops.send_call_func_ipi = xen_smp_send_call_function_ipi;
>  	smp_ops.send_call_func_single_ipi =
> xen_smp_send_call_function_single_ipi;
>  	smp_ops.smp_prepare_boot_cpu = xen_smp_prepare_boot_cpu;
> -- 
> 1.7.7.6
> 
>