Patchwork [1.3] aio: avoid livelock behavior for Win32

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Submitter Paolo Bonzini
Date Nov. 23, 2012, 2:59 p.m.
Message ID <1353682783-25624-1-git-send-email-pbonzini@redhat.com>
Download mbox | patch
Permalink /patch/201336/
State New
Headers show

Comments

Paolo Bonzini - Nov. 23, 2012, 2:59 p.m.
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.

 aio-win32.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)
Anthony Liguori - Nov. 26, 2012, 9:49 p.m.
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

Patch

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;