Re: [Qemu-devel] [PATCH v2 3/4] exec: Notify cpu_register_map_client caller if the bounce buffer is available

[Paolo Bonzini <pbonzini@redhat.com>]

On 13/03/2015 02:38, Fam Zheng wrote:
> The caller's workflow is like
> 
>     if (!address_space_map()) {
>         ...
>         cpu_register_map_client();
>     }
> 
> If bounce buffer became available after address_space_map() but before
> cpu_register_map_client(), the caller could miss it and has to wait for the
> next bounce buffer uesr to release, which may never happen in the worse case.
> 
> Just notify the caller with the passed callback in cpu_register_map_client().
> 
> Signed-off-by: Fam Zheng <famz@redhat.com>
> ---
>  exec.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/exec.c b/exec.c
> index 93ccd5a..82781e4 100644
> --- a/exec.c
> +++ b/exec.c
> @@ -2502,6 +2502,9 @@ void *cpu_register_map_client(void *opaque, void (*callback)(void *opaque))
>      client->opaque = opaque;
>      client->callback = callback;
>      QSLIST_INSERT_HEAD_ATOMIC(&map_client_list, client, link);
> +    if (!atomic_read(&bounce.in_use)) {
> +        callback(opaque);

This should call cpu_notify_map_clients instead, otherwise you get two
calls.

Paolo

> +    }
>      return client;
>  }
>  
>