aio: Fix return value of aio_poll()

aio_poll() must return true if any work is still pending, even if it
didn't make progress, so that bdrv_drain_all() doesn't stop waiting too
early. The possibility of stopping early occasionally lead to a failed
assertion in bdrv_drain_all(), when some in-flight request was missed
and the function didn't really drain all requests.

In order to make that change, the return value as specified in the
function comment must change for blocking = false; fortunately, the
return value of blocking = false callers is only used in test cases, so
this change shouldn't cause any trouble.

Cc: qemu-stable@nongnu.org
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
(cherry picked from commit 2ea9b58f0bc62445b7ace2381b4c4db7d5597e19)

Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com>

diff --git a/aio-posix.c b/aio-posix.c
index 05cc84e121283edc6c9135ee5fcbacadb471985b..13d4572f338c0606f85c690c3c2cacc91b052957 100644 (file)
--- a/aio-posix.c
+++ b/aio-posix.c
@@ -264,5 +264,6 @@ bool aio_poll(AioContext *ctx, bool blocking)
         }
     }
 
-    return progress;
+    assert(progress || busy);
+    return true;
 }

diff --git a/aio-win32.c b/aio-win32.c
index cec4646635b7dd2900d408ac2975a8b78be20612..7886e9829f975671d22066dd07769078e09e4b88 100644 (file)
--- a/aio-win32.c
+++ b/aio-win32.c
@@ -214,5 +214,6 @@ bool aio_poll(AioContext *ctx, bool blocking)
         events[ret - WAIT_OBJECT_0] = events[--count];
     }
 
-    return progress;
+    assert(progress || busy);
+    return true;
 }

diff --git a/qemu-aio.h b/qemu-aio.h
index 3889fe97a4b35f8fba246ffb662a6e781950c8bf..2b6bdbc701e228417d37f8d511912801e65ef713 100644 (file)
--- a/qemu-aio.h
+++ b/qemu-aio.h
@@ -177,16 +177,14 @@ bool aio_pending(AioContext *ctx);
  * aio as a result of executing I/O completion or bh callbacks.
  *
  * If there is no pending AIO operation or completion (bottom half),
- * return false.  If there are pending bottom halves, return true.
+ * return false.  If there are pending AIO operations of bottom halves,
+ * return true.
  *
  * If there are no pending bottom halves, but there are pending AIO
  * operations, it may not be possible to make any progress without
  * blocking.  If @blocking is true, this function will wait until one
  * or more AIO events have completed, to ensure something has moved
  * before returning.
- *
- * If @blocking is false, this function will also return false if the
- * function cannot make any progress without blocking.
  */
 bool aio_poll(AioContext *ctx, bool blocking);
 

diff --git a/tests/test-aio.c b/tests/test-aio.c
index f53c9087072f795e07af6fea850f2f968c06d239..096a6e8e6955458d01b10bb4ab85f578f1a7e5a1 100644 (file)
--- a/tests/test-aio.c
+++ b/tests/test-aio.c
@@ -315,13 +315,13 @@ static void test_wait_event_notifier_noflush(void)
     event_notifier_set(&data.e);
     g_assert(aio_poll(ctx, false));
     g_assert_cmpint(data.n, ==, 1);
-    g_assert(!aio_poll(ctx, false));
+    g_assert(aio_poll(ctx, false));
     g_assert_cmpint(data.n, ==, 1);
 
     event_notifier_set(&data.e);
     g_assert(aio_poll(ctx, false));
     g_assert_cmpint(data.n, ==, 2);
-    g_assert(!aio_poll(ctx, false));
+    g_assert(aio_poll(ctx, false));
     g_assert_cmpint(data.n, ==, 2);
 
     event_notifier_set(&dummy.e);