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, 3 insertions, 3 deletions

diff --git a/block.c b/block.c
index 701f77fe2f..6cc4115510 100644
--- a/block.c
+++ b/block.c
@@ -1192,19 +1192,19 @@ static char *bdrv_child_get_parent_desc(BdrvChild *c)
     return g_strdup_printf("node '%s'", bdrv_get_node_name(parent));
 }
 
-static void bdrv_child_cb_drained_begin(BdrvChild *child)
+static void GRAPH_RDLOCK bdrv_child_cb_drained_begin(BdrvChild *child)
 {
     BlockDriverState *bs = child->opaque;
     bdrv_do_drained_begin_quiesce(bs, NULL);
 }
 
-static bool bdrv_child_cb_drained_poll(BdrvChild *child)
+static bool GRAPH_RDLOCK bdrv_child_cb_drained_poll(BdrvChild *child)
 {
     BlockDriverState *bs = child->opaque;
     return bdrv_drain_poll(bs, NULL, false);
 }
 
-static void bdrv_child_cb_drained_end(BdrvChild *child)
+static void GRAPH_RDLOCK bdrv_child_cb_drained_end(BdrvChild *child)
 {
     BlockDriverState *bs = child->opaque;
     bdrv_drained_end(bs);