[PATCH v2 03/10] util/async: aio_co_enter(): do aio_co_schedule in general case

[Vladimir Sementsov-Ogievskiy]

With the following patch we want to call aio_co_wake() from thread.
And it works bad.
Assume we have no iothreads.
Assume we have a coroutine A, which waits in the yield point for external
aio_co_wake(), and no progress can be done until it happen.
Main thread is in blocking aio_poll() (for example, in blk_read()).

Now, in a separate thread we do aio_co_wake(). It calls  aio_co_enter(),
which goes through last "else" branch and do aio_context_acquire(ctx).

Now we have a deadlock, as aio_poll() will not release the context lock
until some progress is done, and progress can't be done until
aio_co_wake() wake the coroutine A. And it can't because it wait for
aio_context_acquire().

Still, aio_co_schedule() works well in parallel with blocking
aio_poll(). So let's use it in generic case and drop
aio_context_acquire/aio_context_release branch from aio_co_enter().

Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
---
 util/async.c | 11 ++---------
 1 file changed, 2 insertions(+), 9 deletions(-)

diff --git a/util/async.c b/util/async.c
index 674dbefb7c..f05b883a39 100644
--- a/util/async.c
+++ b/util/async.c
@@ -614,19 +614,12 @@ void aio_co_wake(struct Coroutine *co)
 
 void aio_co_enter(AioContext *ctx, struct Coroutine *co)
 {
-    if (ctx != qemu_get_current_aio_context()) {
-        aio_co_schedule(ctx, co);
-        return;
-    }
-
-    if (qemu_in_coroutine()) {
+    if (ctx == qemu_get_current_aio_context() && qemu_in_coroutine()) {
         Coroutine *self = qemu_coroutine_self();
         assert(self != co);
         QSIMPLEQ_INSERT_TAIL(&self->co_queue_wakeup, co, co_queue_next);
     } else {
-        aio_context_acquire(ctx);
-        qemu_aio_coroutine_enter(ctx, co);
-        aio_context_release(ctx);
+        aio_co_schedule(ctx, co);
     }
 }
 
-- 
2.29.2