Instead of taking the writer lock internally, require callers to already
hold it when calling bdrv_root_attach_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>
Message-ID: <20231027155333.420094-5-kwolf@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
---
 include/block/block_int-global-state.h | 13 +++++++------
 block.c                                |  5 +----
 block/block-backend.c                  |  2 ++
 blockjob.c                             |  2 ++
 4 files changed, 12 insertions(+), 10 deletions(-)

diff --git a/include/block/block_int-global-state.h b/include/block/block_int-global-state.h
index 074b677838..afce6c4416 100644
--- a/include/block/block_int-global-state.h
+++ b/include/block/block_int-global-state.h
@@ -196,12 +196,13 @@ BlockJob *backup_job_create(const char *job_id, BlockDriverState *bs,
                             BlockCompletionFunc *cb, void *opaque,
                             JobTxn *txn, Error **errp);
 
-BdrvChild *bdrv_root_attach_child(BlockDriverState *child_bs,
-                                  const char *child_name,
-                                  const BdrvChildClass *child_class,
-                                  BdrvChildRole child_role,
-                                  uint64_t perm, uint64_t shared_perm,
-                                  void *opaque, Error **errp);
+BdrvChild * GRAPH_WRLOCK
+bdrv_root_attach_child(BlockDriverState *child_bs, const char *child_name,
+                       const BdrvChildClass *child_class,
+                       BdrvChildRole child_role,
+                       uint64_t perm, uint64_t shared_perm,
+                       void *opaque, Error **errp);
+
 void GRAPH_WRLOCK bdrv_root_unref_child(BdrvChild *child);
 
 void GRAPH_RDLOCK bdrv_get_cumulative_perm(BlockDriverState *bs, uint64_t *perm,
diff --git a/block.c b/block.c
index d85738b7dc..5f92eb4950 100644
--- a/block.c
+++ b/block.c
@@ -3214,8 +3214,6 @@ BdrvChild *bdrv_root_attach_child(BlockDriverState *child_bs,
 
     GLOBAL_STATE_CODE();
 
-    bdrv_graph_wrlock(child_bs);
-
     child = bdrv_attach_child_common(child_bs, child_name, child_class,
                                    child_role, perm, shared_perm, opaque,
                                    tran, errp);
@@ -3228,9 +3226,8 @@ BdrvChild *bdrv_root_attach_child(BlockDriverState *child_bs,
 
 out:
     tran_finalize(tran, ret);
-    bdrv_graph_wrunlock();
 
-    bdrv_unref(child_bs);
+    bdrv_schedule_unref(child_bs);
 
     return ret < 0 ? NULL : child;
 }
diff --git a/block/block-backend.c b/block/block-backend.c
index 53cf3bb8b8..075a0dfa95 100644
--- a/block/block-backend.c
+++ b/block/block-backend.c
@@ -931,10 +931,12 @@ int blk_insert_bs(BlockBackend *blk, BlockDriverState *bs, Error **errp)
     ThrottleGroupMember *tgm = &blk->public.throttle_group_member;
     GLOBAL_STATE_CODE();
     bdrv_ref(bs);
+    bdrv_graph_wrlock(bs);
     blk->root = bdrv_root_attach_child(bs, "root", &child_root,
                                        BDRV_CHILD_FILTERED | BDRV_CHILD_PRIMARY,
                                        blk->perm, blk->shared_perm,
                                        blk, errp);
+    bdrv_graph_wrunlock();
     if (blk->root == NULL) {
         return -EPERM;
     }
diff --git a/blockjob.c b/blockjob.c
index 5b24de356d..7920f6e500 100644
--- a/blockjob.c
+++ b/blockjob.c
@@ -248,8 +248,10 @@ int block_job_add_bdrv(BlockJob *job, const char *name, BlockDriverState *bs,
         }
         aio_context_acquire(ctx);
     }
+    bdrv_graph_wrlock(bs);
     c = bdrv_root_attach_child(bs, name, &child_job, 0, perm, shared_perm, job,
                                errp);
+    bdrv_graph_wrunlock();
     if (need_context_ops) {
         aio_context_release(ctx);
         if (job->job.aio_context != qemu_get_aio_context()) {
-- 
2.41.0