block: Mark bdrv_co_io_(un)plug() and callers GRAPH_RDLOCK

This adds GRAPH_RDLOCK annotations to declare that callers of
bdrv_co_io_plug() and bdrv_co_io_unplug() need to hold a reader lock for
the graph.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Message-Id: <20230203152202.49054-18-kwolf@redhat.com>
Reviewed-by: Emanuele Giuseppe Esposito <eesposit@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

block/block-backend.c

@@ -2328,6 +2328,7 @@ void coroutine_fn blk_co_io_plug(BlockBackend *blk)
 {
     BlockDriverState *bs = blk_bs(blk);
     IO_CODE();
+    GRAPH_RDLOCK_GUARD();
 
     if (bs) {
         bdrv_co_io_plug(bs);
@@ -2338,6 +2339,7 @@ void coroutine_fn blk_co_io_unplug(BlockBackend *blk)
 {
     BlockDriverState *bs = blk_bs(blk);
     IO_CODE();
+    GRAPH_RDLOCK_GUARD();
 
     if (bs) {
         bdrv_co_io_unplug(bs);

block/io.c

@@ -3153,6 +3153,7 @@ void coroutine_fn bdrv_co_io_plug(BlockDriverState *bs)
 {
     BdrvChild *child;
     IO_CODE();
+    assert_bdrv_graph_readable();
 
     QLIST_FOREACH(child, &bs->children, next) {
         bdrv_co_io_plug(child->bs);
@@ -3170,6 +3171,7 @@ void coroutine_fn bdrv_co_io_unplug(BlockDriverState *bs)
 {
     BdrvChild *child;
     IO_CODE();
+    assert_bdrv_graph_readable();
 
     assert(bs->io_plugged);
     if (qatomic_fetch_dec(&bs->io_plugged) == 1) {

include/block/block-io.h

@@ -233,8 +233,8 @@ void coroutine_fn bdrv_co_leave(BlockDriverState *bs, AioContext *old_ctx);
 
 AioContext *child_of_bds_get_parent_aio_context(BdrvChild *c);
 
-void coroutine_fn bdrv_co_io_plug(BlockDriverState *bs);
-void coroutine_fn bdrv_co_io_unplug(BlockDriverState *bs);
+void coroutine_fn GRAPH_RDLOCK bdrv_co_io_plug(BlockDriverState *bs);
+void coroutine_fn GRAPH_RDLOCK bdrv_co_io_unplug(BlockDriverState *bs);
 
 bool coroutine_fn bdrv_co_can_store_new_dirty_bitmap(BlockDriverState *bs,
                                                      const char *name,

include/block/block_int-common.h

@@ -735,8 +735,9 @@ struct BlockDriver {
                                              BlkdebugEvent event);
 
     /* io queue for linux-aio */
-    void coroutine_fn (*bdrv_co_io_plug)(BlockDriverState *bs);
-    void coroutine_fn (*bdrv_co_io_unplug)(BlockDriverState *bs);
+    void coroutine_fn GRAPH_RDLOCK_PTR (*bdrv_co_io_plug)(BlockDriverState *bs);
+    void coroutine_fn GRAPH_RDLOCK_PTR (*bdrv_co_io_unplug)(
+        BlockDriverState *bs);
 
     /**
      * bdrv_drain_begin is called if implemented in the beginning of a