[PULL for-5.0 1/1] aio-posix: fix io_uring with external events

[Stefan Hajnoczi <stefanha@redhat.com>]

When external event sources are disabled fdmon-io_uring falls back to
fdmon-poll.  The ->need_wait() callback needs to watch for this so it
can return true when external event sources are disabled.

It is also necessary to call ->wait() when AioHandlers have changed
because io_uring is asynchronous and we must submit new sqes.

Both of these changes to ->need_wait() together fix tests/test-aio -p
/aio/external-client, which failed with:

  test-aio: tests/test-aio.c:404: test_aio_external_client: Assertion `aio_poll(ctx, false)' failed.

Reported-by: Julia Suvorova <jusual@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Stefano Garzarella <sgarzare@redhat.com>
Message-id: 20200319163559.117903-1-stefanha@redhat.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
---
 util/fdmon-io_uring.c | 13 ++++++++++++-
 1 file changed, 12 insertions(+), 1 deletion(-)

diff --git a/util/fdmon-io_uring.c b/util/fdmon-io_uring.c
index 893b79b622..7e143ef515 100644
--- a/util/fdmon-io_uring.c
+++ b/util/fdmon-io_uring.c
@@ -290,7 +290,18 @@ static int fdmon_io_uring_wait(AioContext *ctx, AioHandlerList *ready_list,
 
 static bool fdmon_io_uring_need_wait(AioContext *ctx)
 {
-    return io_uring_cq_ready(&ctx->fdmon_io_uring);
+    /* Have io_uring events completed? */
+    if (io_uring_cq_ready(&ctx->fdmon_io_uring)) {
+        return true;
+    }
+
+    /* Do we need to submit new io_uring sqes? */
+    if (!QSLIST_EMPTY_RCU(&ctx->submit_list)) {
+        return true;
+    }
+
+    /* Are we falling back to fdmon-poll? */
+    return atomic_read(&ctx->external_disable_cnt);
 }
 
 static const FDMonOps fdmon_io_uring_ops = {
-- 
2.24.1