block: Mark bdrv_root_unref_child() GRAPH_WRLOCK

Instead of taking the writer lock internally, require callers to already
hold it when calling bdrv_root_unref_child(). These callers will
typically already hold the graph lock once the locking work is
completed, which means that they can't call functions that take it
internally.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Reviewed-by: Emanuele Giuseppe Esposito <eesposit@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Message-ID: <20230911094620.45040-20-kwolf@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

4 files changed, 9 insertions, 4 deletions

diff --git a/block.c b/block.c
index 8e589bb2e4..9ea8333a28 100644
--- a/block.c
+++ b/block.c
@@ -3268,7 +3268,6 @@ void bdrv_root_unref_child(BdrvChild *child)
     BlockDriverState *child_bs = child->bs;
 
     GLOBAL_STATE_CODE();
-    bdrv_graph_wrlock(NULL);
     bdrv_replace_child_noperm(child, NULL);
     bdrv_child_free(child);
 
@@ -3288,8 +3287,7 @@ void bdrv_root_unref_child(BdrvChild *child)
                                     NULL);
     }
 
-    bdrv_graph_wrunlock();
-    bdrv_unref(child_bs);
+    bdrv_schedule_unref(child_bs);
 }
 
 typedef struct BdrvSetInheritsFrom {
@@ -3366,8 +3364,10 @@ void bdrv_unref_child(BlockDriverState *parent, BdrvChild *child)
         return;
     }
 
+    bdrv_graph_wrlock(NULL);
     bdrv_unset_inherits_from(parent, child, NULL);
     bdrv_root_unref_child(child);
+    bdrv_graph_wrunlock();
 }
 
 
diff --git a/block/block-backend.c b/block/block-backend.c
index 8d0282a5d9..c2636f4351 100644
--- a/block/block-backend.c
+++ b/block/block-backend.c
@@ -915,7 +915,10 @@ void blk_remove_bs(BlockBackend *blk)
     blk_drain(blk);
     root = blk->root;
     blk->root = NULL;
+
+    bdrv_graph_wrlock(NULL);
     bdrv_root_unref_child(root);
+    bdrv_graph_wrunlock();
 }
 
 /*
diff --git a/blockjob.c b/blockjob.c
index 25fe8e625d..58c5d64539 100644
--- a/blockjob.c
+++ b/blockjob.c
@@ -198,6 +198,7 @@ void block_job_remove_all_bdrv(BlockJob *job)
      * one to make sure that such a concurrent access does not attempt
      * to process an already freed BdrvChild.
      */
+    bdrv_graph_wrlock(NULL);
     while (job->nodes) {
         GSList *l = job->nodes;
         BdrvChild *c = l->data;
@@ -209,6 +210,7 @@ void block_job_remove_all_bdrv(BlockJob *job)
 
         g_slist_free_1(l);
     }
+    bdrv_graph_wrunlock();
 }
 
 bool block_job_has_bdrv(BlockJob *job, BlockDriverState *bs)
diff --git a/include/block/block_int-global-state.h b/include/block/block_int-global-state.h
index e2304db58b..074b677838 100644
--- a/include/block/block_int-global-state.h
+++ b/include/block/block_int-global-state.h
@@ -202,7 +202,7 @@ BdrvChild *bdrv_root_attach_child(BlockDriverState *child_bs,
                                   BdrvChildRole child_role,
                                   uint64_t perm, uint64_t shared_perm,
                                   void *opaque, Error **errp);
-void bdrv_root_unref_child(BdrvChild *child);
+void GRAPH_WRLOCK bdrv_root_unref_child(BdrvChild *child);
 
 void GRAPH_RDLOCK bdrv_get_cumulative_perm(BlockDriverState *bs, uint64_t *perm,
                                            uint64_t *shared_perm);