Re: [Qemu-devel] [RFC PATCH v4 04/11] cpus: Add a sync version of cpu_remove()

[David Gibson <david@gibson.dropbear.id.au>]

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On Thu, Aug 06, 2015 at 10:57:10AM +0530, Bharata B Rao wrote:
> This sync API will be used by the CPU hotplug code to wait for the CPU to
> completely get removed before flagging the failure to the device_add
> command.
> 
> Sync version of this call is needed to correctly recover from CPU
> realization failures when ->plug() handler fails.
> 
> Signed-off-by: Bharata B Rao <bharata@linux.vnet.ibm.com>
> ---
>  cpus.c            | 14 ++++++++++++++
>  include/qom/cpu.h |  8 ++++++++
>  2 files changed, 22 insertions(+)
> 
> diff --git a/cpus.c b/cpus.c
> index 73ae2e7..9d9644e 100644
> --- a/cpus.c
> +++ b/cpus.c
> @@ -999,6 +999,8 @@ static void *qemu_kvm_cpu_thread_fn(void *arg)
>          qemu_kvm_wait_io_event(cpu);
>          if (cpu->exit && !cpu_can_run(cpu)) {
>              qemu_kvm_destroy_vcpu(cpu);
> +            cpu->created = false;
> +            qemu_cond_signal(&qemu_cpu_cond);
>              qemu_mutex_unlock(&qemu_global_mutex);
>              return NULL;
>          }
> @@ -1104,6 +1106,8 @@ static void *qemu_tcg_cpu_thread_fn(void *arg)
>          }
>          if (remove_cpu) {
>              qemu_tcg_destroy_vcpu(remove_cpu);
> +            cpu->created = false;
> +            qemu_cond_signal(&qemu_cpu_cond);
>              remove_cpu = NULL;
>          }
>      }
> @@ -1283,6 +1287,16 @@ void cpu_remove(CPUState *cpu)
>      qemu_cpu_kick(cpu);
>  }
>  
> +void cpu_remove_sync(CPUState *cpu)
> +{
> +    cpu->stop = true;
> +    cpu->exit = true;
> +    qemu_cpu_kick(cpu);

It would be nicer for this to call the async cpu_remove() above, to
ensure they stay in sync.

> +    while (cpu->created) {
> +        qemu_cond_wait(&qemu_cpu_cond, &qemu_global_mutex);
> +    }
> +}
> +
>  /* For temporary buffers for forming a name */
>  #define VCPU_THREAD_NAME_SIZE 16
>  
> diff --git a/include/qom/cpu.h b/include/qom/cpu.h
> index 136d9fe..65c6852 100644
> --- a/include/qom/cpu.h
> +++ b/include/qom/cpu.h
> @@ -655,6 +655,14 @@ void cpu_resume(CPUState *cpu);
>   */
>  void cpu_remove(CPUState *cpu);
>  
> + /**
> + * cpu_remove_sync:
> + * @cpu: The CPU to remove.
> + *
> + * Requests the CPU to be removed and waits till it is removed.
> + */
> +void cpu_remove_sync(CPUState *cpu);
> +
>  /**
>   * qemu_init_vcpu:
>   * @cpu: The vCPU to initialize.

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson

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