Re: [Qemu-devel] [PATCH v6 06/11] cpu: Add a sync version of cpu_remove()

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

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On Fri, Jan 08, 2016 at 12:25:14PM +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>
> Reviewed-by: David Gibson <david@gibson.dropbear.id.au>
> ---
>  cpus.c            | 12 ++++++++++++
>  include/qom/cpu.h |  8 ++++++++
>  2 files changed, 20 insertions(+)
> 
> diff --git a/cpus.c b/cpus.c
> index 12374af..c829bd6 100644
> --- a/cpus.c
> +++ b/cpus.c
> @@ -1067,6 +1067,8 @@ 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);

I know I reviewed this earlier, but I suspect this needs to be
qemu_cond_broadcast.  qemu_cpu_cond is global, so there could (at
least in theory) be multiple things waiting on it, and we don't know
which one is waiting on *this* cpu, rather than another one (or on any
other condition handled by this qemu_cpu_cond).

>              qemu_mutex_unlock_iothread();
>              return NULL;
>          }
> @@ -1171,6 +1173,8 @@ 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;
>          }
>      }
> @@ -1336,6 +1340,14 @@ void cpu_remove(CPUState *cpu)
>      qemu_cpu_kick(cpu);
>  }
>  
> +void cpu_remove_sync(CPUState *cpu)
> +{
> +    cpu_remove(cpu);
> +    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 67e05b0..7fc6696 100644
> --- a/include/qom/cpu.h
> +++ b/include/qom/cpu.h
> @@ -705,6 +705,14 @@ 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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