Re: [Qemu-devel] [PATCH 1.3] aio: avoid livelock behavior for Win32

[Anthony Liguori <aliguori@us.ibm.com>]

Paolo Bonzini <pbonzini@redhat.com> writes:

> The repeated calls to WaitForMultipleObjects may cause a livelock in aio_poll,
> where no progress is made on bottom halves.  This patch matches the behavior
> of the POSIX code.
>
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> ---
>         Found by the new unit tests.

Applied. Thanks.

Regards,

Anthony Liguori

>
>  aio-win32.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
>
> diff --git a/aio-win32.c b/aio-win32.c
> index a84eb71..cec4646 100644
> --- a/aio-win32.c
> +++ b/aio-win32.c
> @@ -173,7 +173,7 @@ bool aio_poll(AioContext *ctx, bool blocking)
>      }
>  
>      /* wait until next event */
> -    for (;;) {
> +    while (count > 0) {
>          int timeout = blocking ? INFINITE : 0;
>          int ret = WaitForMultipleObjects(count, events, FALSE, timeout);
>  
> @@ -209,6 +209,9 @@ bool aio_poll(AioContext *ctx, bool blocking)
>                  g_free(tmp);
>              }
>          }
> +
> +        /* Try again, but only call each handler once.  */
> +        events[ret - WAIT_OBJECT_0] = events[--count];
>      }
>  
>      return progress;
> -- 
> 1.8.0