Re: [Qemu-devel] [PATCH v3 2/4] exec: Protect map_client_list with mutex

[Paolo Bonzini <pbonzini@redhat.com>]

On 16/03/2015 06:31, Fam Zheng wrote:
> So that accesses from multiple threads are safe.
> 
> Signed-off-by: Fam Zheng <famz@redhat.com>
> ---
>  exec.c | 24 +++++++++++++++---------
>  1 file changed, 15 insertions(+), 9 deletions(-)
> 
> diff --git a/exec.c b/exec.c
> index 4080044..3e54580 100644
> --- a/exec.c
> +++ b/exec.c
> @@ -429,15 +429,6 @@ address_space_translate_for_iotlb(CPUState *cpu, hwaddr addr,
>  }
>  #endif
>  
> -void cpu_exec_init_all(void)
> -{
> -#if !defined(CONFIG_USER_ONLY)
> -    qemu_mutex_init(&ram_list.mutex);
> -    memory_map_init();
> -    io_mem_init();
> -#endif
> -}
> -
>  #if !defined(CONFIG_USER_ONLY)
>  
>  static int cpu_common_post_load(void *opaque, int version_id)
> @@ -2494,6 +2485,7 @@ typedef struct MapClient {
>      QLIST_ENTRY(MapClient) link;
>  } MapClient;
>  
> +QemuMutex map_client_list_lock;
>  static QLIST_HEAD(map_client_list, MapClient) map_client_list
>      = QLIST_HEAD_INITIALIZER(map_client_list);
>  
> @@ -2501,12 +2493,24 @@ void *cpu_register_map_client(void *opaque, void (*callback)(void *opaque))
>  {
>      MapClient *client = g_malloc(sizeof(*client));
>  
> +    qemu_mutex_lock(&map_client_list_lock);
>      client->opaque = opaque;
>      client->callback = callback;
>      QLIST_INSERT_HEAD(&map_client_list, client, link);
> +    qemu_mutex_unlock(&map_client_list_lock);
>      return client;
>  }
>  
> +void cpu_exec_init_all(void)
> +{
> +#if !defined(CONFIG_USER_ONLY)
> +    qemu_mutex_init(&ram_list.mutex);
> +    memory_map_init();
> +    io_mem_init();
> +#endif
> +    qemu_mutex_init(&map_client_list_lock);
> +}
> +

You are moving cpu_exec_init_all within an #ifndef CONFIG_USER_ONLY.
Does this patch compile for user-mode emulation?

The move itself is okay but only if you remove the two calls in
*-user/main.c (and possibly move the prototype to include/exec/exec-all.h).

>  static void cpu_unregister_map_client(void *_client)
>  {
>      MapClient *client = (MapClient *)_client;
> @@ -2519,11 +2523,13 @@ static void cpu_notify_map_clients(void)
>  {
>      MapClient *client;
>  
> +    qemu_mutex_lock(&map_client_list_lock);
>      while (!QLIST_EMPTY(&map_client_list)) {
>          client = QLIST_FIRST(&map_client_list);
>          client->callback(client->opaque);

A good rule of thumb is never hold a lock while calling "unknown" code.
 This will be fixed in patch 4, so it's okay.

Paolo

>          cpu_unregister_map_client(client);
>      }
> +    qemu_mutex_unlock(&map_client_list_lock);
>  }
>  
>  bool address_space_access_valid(AddressSpace *as, hwaddr addr, int len, bool is_write)
>