block: Mark drain related functions GRAPH_RDLOCK

Draining recursively traverses the graph, therefore we need to make sure
that also such accesses to the graph are protected by the graph rdlock.

There are 3 different drain callers to consider:
1. drain in the main loop: no issue at all, rdlock is nop.
2. drain in an iothread: rdlock only works in main loop or coroutines,
   so disallow it.
3. drain in a coroutine (regardless of AioContext): the drain mechanism
   takes care of scheduling a BH in the bs->aio_context that will
   then take care of perform the actual draining. This is wrong,
   because as pointed in (2) if bs->aio_context is an iothread then
   rdlock won't work. Therefore change bdrv_co_yield_to_drain to
   schedule the BH in the main loop.

Caller (2) also implies that we need to modify test-bdrv-drain.c to
disallow draining in the iothreads.

For some places, we know that they will hold the lock, but we don't have
the GRAPH_RDLOCK annotations yet. In this case, add assume_graph_lock()
with a FIXME comment. These places will be removed once everything is
properly annotated.

Signed-off-by: Emanuele Giuseppe Esposito <eesposit@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Message-ID: <20230929145157.45443-6-kwolf@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

1 files changed, 2 insertions, 2 deletions

diff --git a/tests/unit/test-bdrv-drain.c b/tests/unit/test-bdrv-drain.c
index bdd3757615..d734829778 100644
--- a/tests/unit/test-bdrv-drain.c
+++ b/tests/unit/test-bdrv-drain.c
@@ -1196,7 +1196,7 @@ static void coroutine_mixed_fn detach_by_parent_aio_cb(void *opaque, int ret)
     }
 }
 
-static void detach_by_driver_cb_drained_begin(BdrvChild *child)
+static void GRAPH_RDLOCK detach_by_driver_cb_drained_begin(BdrvChild *child)
 {
     struct detach_by_parent_data *data = &detach_by_parent_data;
 
@@ -1233,7 +1233,7 @@ static BdrvChildClass detach_by_driver_cb_class;
  *     state is messed up, but if it is only polled in the single
  *     BDRV_POLL_WHILE() at the end of the drain, this should work fine.
  */
-static void test_detach_indirect(bool by_parent_cb)
+static void TSA_NO_TSA test_detach_indirect(bool by_parent_cb)
 {
     BlockBackend *blk;
     BlockDriverState *parent_a, *parent_b, *a, *b, *c;