block: Mark bdrv_primary_child() and callers GRAPH_RDLOCK

This adds GRAPH_RDLOCK annotations to declare that callers of
bdrv_primary_child() need to hold a reader lock for the graph
because it accesses the children list of a node.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Message-ID: <20230929145157.45443-12-kwolf@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

3 files changed, 16 insertions, 3 deletions

diff --git a/block.c b/block.c
index 142e1d5e2b..6ce3e2ad7a 100644
--- a/block.c
+++ b/block.c
@@ -6692,7 +6692,8 @@ void coroutine_fn bdrv_co_debug_event(BlockDriverState *bs, BlkdebugEvent event)
     bs->drv->bdrv_co_debug_event(bs, event);
 }
 
-static BlockDriverState *bdrv_find_debug_node(BlockDriverState *bs)
+static BlockDriverState * GRAPH_RDLOCK
+bdrv_find_debug_node(BlockDriverState *bs)
 {
     GLOBAL_STATE_CODE();
     while (bs && bs->drv && !bs->drv->bdrv_debug_breakpoint) {
@@ -6711,6 +6712,8 @@ int bdrv_debug_breakpoint(BlockDriverState *bs, const char *event,
                           const char *tag)
 {
     GLOBAL_STATE_CODE();
+    GRAPH_RDLOCK_GUARD_MAINLOOP();
+
     bs = bdrv_find_debug_node(bs);
     if (bs) {
         return bs->drv->bdrv_debug_breakpoint(bs, event, tag);
@@ -6722,6 +6725,8 @@ int bdrv_debug_breakpoint(BlockDriverState *bs, const char *event,
 int bdrv_debug_remove_breakpoint(BlockDriverState *bs, const char *tag)
 {
     GLOBAL_STATE_CODE();
+    GRAPH_RDLOCK_GUARD_MAINLOOP();
+
     bs = bdrv_find_debug_node(bs);
     if (bs) {
         return bs->drv->bdrv_debug_remove_breakpoint(bs, tag);
@@ -6733,6 +6738,8 @@ int bdrv_debug_remove_breakpoint(BlockDriverState *bs, const char *tag)
 int bdrv_debug_resume(BlockDriverState *bs, const char *tag)
 {
     GLOBAL_STATE_CODE();
+    GRAPH_RDLOCK_GUARD_MAINLOOP();
+
     while (bs && (!bs->drv || !bs->drv->bdrv_debug_resume)) {
         bs = bdrv_primary_bs(bs);
     }
@@ -6747,6 +6754,8 @@ int bdrv_debug_resume(BlockDriverState *bs, const char *tag)
 bool bdrv_debug_is_suspended(BlockDriverState *bs, const char *tag)
 {
     GLOBAL_STATE_CODE();
+    GRAPH_RDLOCK_GUARD_MAINLOOP();
+
     while (bs && bs->drv && !bs->drv->bdrv_debug_is_suspended) {
         bs = bdrv_primary_bs(bs);
     }
diff --git a/block/snapshot.c b/block/snapshot.c
index 554065578b..ad2bf6e068 100644
--- a/block/snapshot.c
+++ b/block/snapshot.c
@@ -311,7 +311,10 @@ int bdrv_snapshot_goto(BlockDriverState *bs,
          * respective option (with the qdict_put_str() call above).
          * Assert that .bdrv_open() has attached the right BDS as primary child.
          */
+        bdrv_graph_rdlock_main_loop();
         assert(bdrv_primary_bs(bs) == fallback_bs);
+        bdrv_graph_rdunlock_main_loop();
+
         bdrv_unref(fallback_bs);
         return ret;
     }
diff --git a/include/block/block_int-io.h b/include/block/block_int-io.h
index eb0da7232e..2b6004ab93 100644
--- a/include/block/block_int-io.h
+++ b/include/block/block_int-io.h
@@ -133,7 +133,7 @@ bdrv_refresh_total_sectors(BlockDriverState *bs, int64_t hint);
 BdrvChild *bdrv_cow_child(BlockDriverState *bs);
 BdrvChild *bdrv_filter_child(BlockDriverState *bs);
 BdrvChild *bdrv_filter_or_cow_child(BlockDriverState *bs);
-BdrvChild *bdrv_primary_child(BlockDriverState *bs);
+BdrvChild * GRAPH_RDLOCK bdrv_primary_child(BlockDriverState *bs);
 BlockDriverState *bdrv_skip_filters(BlockDriverState *bs);
 BlockDriverState *bdrv_backing_chain_next(BlockDriverState *bs);
 
@@ -155,7 +155,8 @@ static inline BlockDriverState *bdrv_filter_or_cow_bs(BlockDriverState *bs)
     return child_bs(bdrv_filter_or_cow_child(bs));
 }
 
-static inline BlockDriverState *bdrv_primary_bs(BlockDriverState *bs)
+static inline BlockDriverState * GRAPH_RDLOCK
+bdrv_primary_bs(BlockDriverState *bs)
 {
     IO_CODE();
     return child_bs(bdrv_primary_child(bs));