Re: [PATCH v5 29/45] x86/xen: Use get/put_online_cpus_atomic() toprevent CPU offline

[Konrad Rzeszutek Wilk]

On Tue, Jan 22, 2013 at 01:10:51PM +0530, Srivatsa S. Bhat wrote:
> Once stop_machine() is gone from the CPU offline path, we won't be able to
> depend on preempt_disable() or local_irq_disable() to prevent CPUs from
> going offline from under us.
> 
> Use the get/put_online_cpus_atomic() APIs to prevent CPUs from going offline,
> while invoking from atomic context.
> 
> Cc: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>

Weird. I see this in the patch but I don't see it in the header? Did you
explicitly suppress the CC part?


Anyhow, the patch looks sane enough, thought I need to to run it through
a test framework just to be on a sure side.

> Cc: Jeremy Fitzhardinge <jeremy@xxxxxxxx>
> Cc: "H. Peter Anvin" <hpa@xxxxxxxxx>
> Cc: x86@xxxxxxxxxx
> Cc: xen-devel@xxxxxxxxxxxxxxxxxxx
> Cc: virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx
> Signed-off-by: Srivatsa S. Bhat <srivatsa.bhat@xxxxxxxxxxxxxxxxxx>
> ---
> 
>  arch/x86/xen/mmu.c |   11 +++++++++--
>  arch/x86/xen/smp.c |    9 +++++++++
>  2 files changed, 18 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/x86/xen/mmu.c b/arch/x86/xen/mmu.c
> index 01de35c..6a95a15 100644
> --- a/arch/x86/xen/mmu.c
> +++ b/arch/x86/xen/mmu.c
> @@ -39,6 +39,7 @@
>   * Jeremy Fitzhardinge <jeremy@xxxxxxxxxxxxx>, XenSource Inc, 2007
>   */
>  #include <linux/sched.h>
> +#include <linux/cpu.h>
>  #include <linux/highmem.h>
>  #include <linux/debugfs.h>
>  #include <linux/bug.h>
> @@ -1163,9 +1164,13 @@ static void xen_drop_mm_ref(struct mm_struct *mm)
>   */
>  static void xen_exit_mmap(struct mm_struct *mm)
>  {
> -	get_cpu();		/* make sure we don't move around */
> +	/*
> +	 * Make sure we don't move around, and prevent CPUs from going
> +	 * offline.
> +	 */
> +	get_online_cpus_atomic();
>  	xen_drop_mm_ref(mm);
> -	put_cpu();
> +	put_online_cpus_atomic();
>  
>  	spin_lock(&mm->page_table_lock);
>  
> @@ -1371,6 +1376,7 @@ static void xen_flush_tlb_others(const struct cpumask *cpus,
>  	args->op.arg2.vcpumask = to_cpumask(args->mask);
>  
>  	/* Remove us, and any offline CPUS. */
> +	get_online_cpus_atomic();
>  	cpumask_and(to_cpumask(args->mask), cpus, cpu_online_mask);
>  	cpumask_clear_cpu(smp_processor_id(), to_cpumask(args->mask));
>  
> @@ -1383,6 +1389,7 @@ static void xen_flush_tlb_others(const struct cpumask *cpus,
>  	MULTI_mmuext_op(mcs.mc, &args->op, 1, NULL, DOMID_SELF);
>  
>  	xen_mc_issue(PARAVIRT_LAZY_MMU);
> +	put_online_cpus_atomic();
>  }
>  
>  static unsigned long xen_read_cr3(void)
> diff --git a/arch/x86/xen/smp.c b/arch/x86/xen/smp.c
> index 4f7d259..7d753ae 100644
> --- a/arch/x86/xen/smp.c
> +++ b/arch/x86/xen/smp.c
> @@ -16,6 +16,7 @@
>  #include <linux/err.h>
>  #include <linux/slab.h>
>  #include <linux/smp.h>
> +#include <linux/cpu.h>
>  #include <linux/irq_work.h>
>  
>  #include <asm/paravirt.h>
> @@ -487,8 +488,10 @@ static void __xen_send_IPI_mask(const struct cpumask *mask,
>  {
>  	unsigned cpu;
>  
> +	get_online_cpus_atomic();
>  	for_each_cpu_and(cpu, mask, cpu_online_mask)
>  		xen_send_IPI_one(cpu, vector);
> +	put_online_cpus_atomic();
>  }
>  
>  static void xen_smp_send_call_function_ipi(const struct cpumask *mask)
> @@ -551,8 +554,10 @@ void xen_send_IPI_all(int vector)
>  {
>  	int xen_vector = xen_map_vector(vector);
>  
> +	get_online_cpus_atomic();
>  	if (xen_vector >= 0)
>  		__xen_send_IPI_mask(cpu_online_mask, xen_vector);
> +	put_online_cpus_atomic();
>  }
>  
>  void xen_send_IPI_self(int vector)
> @@ -572,20 +577,24 @@ void xen_send_IPI_mask_allbutself(const struct cpumask *mask,
>  	if (!(num_online_cpus() > 1))
>  		return;
>  
> +	get_online_cpus_atomic();
>  	for_each_cpu_and(cpu, mask, cpu_online_mask) {
>  		if (this_cpu == cpu)
>  			continue;
>  
>  		xen_smp_send_call_function_single_ipi(cpu);
>  	}
> +	put_online_cpus_atomic();
>  }
>  
>  void xen_send_IPI_allbutself(int vector)
>  {
>  	int xen_vector = xen_map_vector(vector);
>  
> +	get_online_cpus_atomic();
>  	if (xen_vector >= 0)
>  		xen_send_IPI_mask_allbutself(cpu_online_mask, xen_vector);
> +	put_online_cpus_atomic();
>  }
>  
>  static irqreturn_t xen_call_function_interrupt(int irq, void *dev_id)
> 
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