[Qemu-devel] [PATCH 04/14] job: Use AIO_WAIT_WHILE() in job_finish_sync()

[Kevin Wolf <kwolf@redhat.com>]

job_finish_sync() needs to release the AioContext lock of the job before
calling aio_poll(). Otherwise, callbacks called by aio_poll() would
possibly take the lock a second time and run into a deadlock with a
nested AIO_WAIT_WHILE() call.

Also, job_drain() without aio_poll() isn't necessarily enough to make
progress on a job, it could depend on bottom halves to be executed.

Combine both open-coded while loops into a single AIO_WAIT_WHILE() call
that solves both of these problems.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
---
 job.c | 14 ++++++--------
 1 file changed, 6 insertions(+), 8 deletions(-)

diff --git a/job.c b/job.c
index 9ad0b7476a..8480eda188 100644
--- a/job.c
+++ b/job.c
@@ -29,6 +29,7 @@
 #include "qemu/job.h"
 #include "qemu/id.h"
 #include "qemu/main-loop.h"
+#include "block/aio-wait.h"
 #include "trace-root.h"
 #include "qapi/qapi-events-job.h"
 
@@ -998,6 +999,7 @@ void job_defer_to_main_loop(Job *job, JobDeferToMainLoopFn *fn, void *opaque)
 int job_finish_sync(Job *job, void (*finish)(Job *, Error **errp), Error **errp)
 {
     Error *local_err = NULL;
+    AioWait dummy_wait = {};
     int ret;
 
     job_ref(job);
@@ -1010,14 +1012,10 @@ int job_finish_sync(Job *job, void (*finish)(Job *, Error **errp), Error **errp)
         job_unref(job);
         return -EBUSY;
     }
-    /* job_drain calls job_enter, and it should be enough to induce progress
-     * until the job completes or moves to the main thread. */
-    while (!job->deferred_to_main_loop && !job_is_completed(job)) {
-        job_drain(job);
-    }
-    while (!job_is_completed(job)) {
-        aio_poll(qemu_get_aio_context(), true);
-    }
+
+    AIO_WAIT_WHILE(&dummy_wait, job->aio_context,
+                   (job_drain(job), !job_is_completed(job)));
+
     ret = (job_is_cancelled(job) && job->ret == 0) ? -ECANCELED : job->ret;
     job_unref(job);
     return ret;
-- 
2.13.6