qcow2: Fix open with 'file' in iothread

qcow2_open() doesn't work correctly when opening the 'file' child moves
bs to an iothread, for several reasons:

- It uses BDRV_POLL_WHILE() to wait for the qcow2_open_entry()
  coroutine, which involves dropping the AioContext lock for bs when it
  is not in the main context - but we don't hold it, so this crashes.

- It runs the qcow2_open_entry() coroutine in the current thread instead
  of the new AioContext of bs.

- qcow2_open_entry() doesn't notify the main loop when it's done.

This patches fixes these issues around delegating work to a coroutine.
Temporarily dropping the main AioContext lock is not necessary because
we know we run in the main thread.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Message-Id: <20230525124713.401149-7-kwolf@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

1 files changed, 6 insertions, 2 deletions

diff --git a/block/qcow2.c b/block/qcow2.c
index b00b4e7..7f39483 100644
--- a/block/qcow2.c
+++ b/block/qcow2.c
@@ -1904,6 +1904,8 @@ static void coroutine_fn qcow2_open_entry(void *opaque)
     qoc->ret = qcow2_do_open(qoc->bs, qoc->options, qoc->flags, true,
                              qoc->errp);
     qemu_co_mutex_unlock(&s->lock);
+
+    aio_wait_kick();
 }
 
 static int qcow2_open(BlockDriverState *bs, QDict *options, int flags,
@@ -1929,8 +1931,10 @@ static int qcow2_open(BlockDriverState *bs, QDict *options, int flags,
 
     assert(!qemu_in_coroutine());
     assert(qemu_get_current_aio_context() == qemu_get_aio_context());
-    qemu_coroutine_enter(qemu_coroutine_create(qcow2_open_entry, &qoc));
-    BDRV_POLL_WHILE(bs, qoc.ret == -EINPROGRESS);
+
+    aio_co_enter(bdrv_get_aio_context(bs),
+                 qemu_coroutine_create(qcow2_open_entry, &qoc));
+    AIO_WAIT_WHILE_UNLOCKED(NULL, qoc.ret == -EINPROGRESS);
 
     return qoc.ret;
 }