Re: [Qemu-ppc] [RFC PATCH v4 01/11] exec: Remove cpu from cpus list during cpu_exec_exit()

[David Gibson]

On Thu, Aug 06, 2015 at 10:57:07AM +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.
> 
> Instead of introducing a new field CPUState.queued, I could have used
> CPUState.cpu_index to check if the cpu is already dequeued from the list.
> Since that doesn't work for CONFIG_USER_ONLY, I had to add a new field.
> 
> Signed-off-by: Bharata B Rao <address@hidden>

This seems reasonable to me, but I'm wondering how x86 cpu hotplug /
unplug is working without it.

> ---
>  exec.c            | 11 +++++++++++
>  include/qom/cpu.h |  1 +
>  2 files changed, 12 insertions(+)
> 
> diff --git a/exec.c b/exec.c
> index 0a4a0c5..b196d68 100644
> --- a/exec.c
> +++ b/exec.c
> @@ -550,6 +550,10 @@ void cpu_exec_exit(CPUState *cpu)
>          return;
>      }
>  
> +    if (cpu->queued) {
> +        QTAILQ_REMOVE(&cpus, cpu, node);
> +        cpu->queued = false;
> +    }
>      bitmap_clear(cpu_index_map, cpu->cpu_index, 1);
>      cpu->cpu_index = -1;
>  }
> @@ -568,6 +572,12 @@ static int cpu_get_free_index(Error **errp)
>  
>  void cpu_exec_exit(CPUState *cpu)
>  {
> +    cpu_list_lock();
> +    if (cpu->queued) {
> +        QTAILQ_REMOVE(&cpus, cpu, node);
> +        cpu->queued = false;
> +    }
> +    cpu_list_unlock();
>  }
>  #endif
>  
> @@ -595,6 +605,7 @@ void cpu_exec_init(CPUState *cpu, Error **errp)
>          return;
>      }
>      QTAILQ_INSERT_TAIL(&cpus, cpu, node);
> +    cpu->queued = true;
>  #if defined(CONFIG_USER_ONLY)
>      cpu_list_unlock();
>  #endif
> diff --git a/include/qom/cpu.h b/include/qom/cpu.h
> index 20aabc9..a00e3a8 100644
> --- a/include/qom/cpu.h
> +++ b/include/qom/cpu.h
> @@ -284,6 +284,7 @@ struct CPUState {
>      int gdb_num_regs;
>      int gdb_num_g_regs;
>      QTAILQ_ENTRY(CPUState) node;
> +    bool queued;
>  
>      /* ice debug support */
>      QTAILQ_HEAD(breakpoints_head, CPUBreakpoint) breakpoints;

-- 
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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