Re: [Qemu-devel] [PATCH v7 02/13] exec: Remove cpu from cpus list during cpu_exec_exit()

[Eduardo Habkost]

On Thu, Jan 28, 2016 at 11:19:44AM +0530, Bharata B Rao wrote:
> CPUState *cpu gets added to the cpus list during cpu_exec_init(). It
> should be removed from cpu_exec_exit().
> 
> cpu_exec_init() is called from generic CPU::instance_finalize and some
> archs like PowerPC call it from CPU unrealizefn. So ensure that we
> dequeue the cpu only once.
> 
> Now -1 value for cpu->cpu_index indicates that we have already dequeued
> the cpu for CONFIG_USER_ONLY case also.
> 
> Signed-off-by: Bharata B Rao <address@hidden>
> Reviewed-by: David Gibson <address@hidden>
> ---
>  exec.c | 10 ++++++++++
>  1 file changed, 10 insertions(+)
> 
> diff --git a/exec.c b/exec.c
> index 7115403..c8da9d4 100644
> --- a/exec.c
> +++ b/exec.c
> @@ -596,6 +596,7 @@ void cpu_exec_exit(CPUState *cpu)
>          return;
>      }
>  
> +    QTAILQ_REMOVE(&cpus, cpu, node);
>      bitmap_clear(cpu_index_map, cpu->cpu_index, 1);
>      cpu->cpu_index = -1;
>  }
> @@ -614,6 +615,15 @@ static int cpu_get_free_index(Error **errp)
>  
>  void cpu_exec_exit(CPUState *cpu)
>  {
> +    cpu_list_lock();
> +    if (cpu->cpu_index == -1) {
> +        cpu_list_unlock();
> +        return;
> +    }
> +
> +    QTAILQ_REMOVE(&cpus, cpu, node);
> +    cpu->cpu_index = -1;
> +    cpu_list_unlock();

With this, the only differences between the two cpu_exec_exit()
implementations are:

* cpu_list_lock()/cpu_list_unlock() functions.
  * We can add !CONFIG_USER_ONLY stubs for them.
* The bitmap_clear() call.
  * It can be abstracted away in a cpu_release_index() function,
    just like we already have a CONFIG_USER_ONLY version of
    cpu_get_free_index().
    * I was going to suggest using cpu_index_map on
      CONFIG_USER_ONLY too, but I assume we don't want to limit
      the number of threads in *-user to MAX_CPUMASK_BITS.

This way we won't need to duplicate cpu_exec_exit() code.

-- 
Eduardo