block: Mark bdrv_first_blk() and bdrv_is_root_node() GRAPH_RDLOCK

This adds GRAPH_RDLOCK annotations to declare that callers of
bdrv_first_blk() and bdrv_is_root_node() need to hold a reader lock
for the graph. These functions are the only functions in block-backend.c
that access the parent list of a node.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Message-ID: <20230929145157.45443-5-kwolf@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

7 files changed, 33 insertions, 7 deletions

diff --git a/block/block-backend.c b/block/block-backend.c
index efe2e7cbf8..39b5f90a11 100644
--- a/block/block-backend.c
+++ b/block/block-backend.c
@@ -780,11 +780,12 @@ BlockDriverState *blk_bs(BlockBackend *blk)
     return blk->root ? blk->root->bs : NULL;
 }
 
-static BlockBackend *bdrv_first_blk(BlockDriverState *bs)
+static BlockBackend * GRAPH_RDLOCK bdrv_first_blk(BlockDriverState *bs)
 {
     BdrvChild *child;
 
     GLOBAL_STATE_CODE();
+    assert_bdrv_graph_readable();
 
     QLIST_FOREACH(child, &bs->parents, next_parent) {
         if (child->klass == &child_root) {
@@ -812,6 +813,8 @@ bool bdrv_is_root_node(BlockDriverState *bs)
     BdrvChild *c;
 
     GLOBAL_STATE_CODE();
+    assert_bdrv_graph_readable();
+
     QLIST_FOREACH(c, &bs->parents, next_parent) {
         if (c->klass != &child_root) {
             return false;
@@ -2259,6 +2262,7 @@ void blk_activate(BlockBackend *blk, Error **errp)
     if (qemu_in_coroutine()) {
         bdrv_co_activate(bs, errp);
     } else {
+        GRAPH_RDLOCK_GUARD_MAINLOOP();
         bdrv_activate(bs, errp);
     }
 }
diff --git a/block/export/export.c b/block/export/export.c
index 10316b43c5..a8f274e526 100644
--- a/block/export/export.c
+++ b/block/export/export.c
@@ -83,6 +83,8 @@ BlockExport *blk_exp_add(BlockExportOptions *export, Error **errp)
     uint64_t perm;
     int ret;
 
+    GLOBAL_STATE_CODE();
+
     if (!id_wellformed(export->id)) {
         error_setg(errp, "Invalid block export id");
         return NULL;
@@ -145,7 +147,9 @@ BlockExport *blk_exp_add(BlockExportOptions *export, Error **errp)
      * access since the export could be available before migration handover.
      * ctx was acquired in the caller.
      */
+    bdrv_graph_rdlock_main_loop();
     bdrv_activate(bs, NULL);
+    bdrv_graph_rdunlock_main_loop();
 
     perm = BLK_PERM_CONSISTENT_READ;
     if (export->writable) {
diff --git a/block/io.c b/block/io.c
index 9e170929a7..5821a4d1f5 100644
--- a/block/io.c
+++ b/block/io.c
@@ -2330,6 +2330,7 @@ int bdrv_flush_all(void)
     int result = 0;
 
     GLOBAL_STATE_CODE();
+    GRAPH_RDLOCK_GUARD_MAINLOOP();
 
     /*
      * bdrv queue is managed by record/replay,
diff --git a/block/monitor/block-hmp-cmds.c b/block/monitor/block-hmp-cmds.c
index ca2599de44..6b7d7dd072 100644
--- a/block/monitor/block-hmp-cmds.c
+++ b/block/monitor/block-hmp-cmds.c
@@ -896,6 +896,8 @@ void hmp_info_snapshots(Monitor *mon, const QDict *qdict)
     SnapshotEntry *snapshot_entry;
     Error *err = NULL;
 
+    GRAPH_RDLOCK_GUARD_MAINLOOP();
+
     bs = bdrv_all_find_vmstate_bs(NULL, false, NULL, &err);
     if (!bs) {
         error_report_err(err);
diff --git a/block/qapi-sysemu.c b/block/qapi-sysemu.c
index ef07151892..e885a64c32 100644
--- a/block/qapi-sysemu.c
+++ b/block/qapi-sysemu.c
@@ -279,6 +279,8 @@ static void blockdev_insert_medium(const char *device, const char *id,
     BlockBackend *blk;
     BlockDriverState *bs;
 
+    GRAPH_RDLOCK_GUARD_MAINLOOP();
+
     blk = qmp_get_blk(device, id, errp);
     if (!blk) {
         return;
diff --git a/block/replication.c b/block/replication.c
index 4ad3dd5115..107445d0ce 100644
--- a/block/replication.c
+++ b/block/replication.c
@@ -458,6 +458,8 @@ static void replication_start(ReplicationState *rs, ReplicationMode mode,
     Error *local_err = NULL;
     BackupPerf perf = { .use_copy_range = true, .max_workers = 1 };
 
+    GLOBAL_STATE_CODE();
+
     aio_context = bdrv_get_aio_context(bs);
     aio_context_acquire(aio_context);
     s = bs->opaque;
@@ -504,12 +506,15 @@ static void replication_start(ReplicationState *rs, ReplicationMode mode,
             return;
         }
 
+        bdrv_graph_rdlock_main_loop();
         secondary_disk = hidden_disk->bs->backing;
         if (!secondary_disk->bs || !bdrv_has_blk(secondary_disk->bs)) {
             error_setg(errp, "The secondary disk doesn't have block backend");
+            bdrv_graph_rdunlock_main_loop();
             aio_context_release(aio_context);
             return;
         }
+        bdrv_graph_rdunlock_main_loop();
 
         /* verify the length */
         active_length = bdrv_getlength(active_disk->bs);
@@ -566,8 +571,6 @@ static void replication_start(ReplicationState *rs, ReplicationMode mode,
             return;
         }
 
-        bdrv_graph_wrunlock();
-
         /* start backup job now */
         error_setg(&s->blocker,
                    "Block device is in use by internal backup job");
@@ -576,6 +579,7 @@ static void replication_start(ReplicationState *rs, ReplicationMode mode,
         if (!top_bs || !bdrv_is_root_node(top_bs) ||
             !check_top_bs(top_bs, bs)) {
             error_setg(errp, "No top_bs or it is invalid");
+            bdrv_graph_wrunlock();
             reopen_backing_file(bs, false, NULL);
             aio_context_release(aio_context);
             return;
@@ -583,6 +587,8 @@ static void replication_start(ReplicationState *rs, ReplicationMode mode,
         bdrv_op_block_all(top_bs, s->blocker);
         bdrv_op_unblock(top_bs, BLOCK_OP_TYPE_DATAPLANE, s->blocker);
 
+        bdrv_graph_wrunlock();
+
         s->backup_job = backup_job_create(
                                 NULL, s->secondary_disk->bs, s->hidden_disk->bs,
                                 0, MIRROR_SYNC_MODE_NONE, NULL, 0, false, NULL,
diff --git a/block/snapshot.c b/block/snapshot.c
index b86b5b24ad..633391e8a9 100644
--- a/block/snapshot.c
+++ b/block/snapshot.c
@@ -462,9 +462,9 @@ int bdrv_snapshot_load_tmp_by_id_or_name(BlockDriverState *bs,
 }
 
 
-static int bdrv_all_get_snapshot_devices(bool has_devices, strList *devices,
-                                         GList **all_bdrvs,
-                                         Error **errp)
+static int GRAPH_RDLOCK
+bdrv_all_get_snapshot_devices(bool has_devices, strList *devices,
+                              GList **all_bdrvs, Error **errp)
 {
     g_autoptr(GList) bdrvs = NULL;
 
@@ -496,7 +496,7 @@ static int bdrv_all_get_snapshot_devices(bool has_devices, strList *devices,
 }
 
 
-static bool bdrv_all_snapshots_includes_bs(BlockDriverState *bs)
+static bool GRAPH_RDLOCK bdrv_all_snapshots_includes_bs(BlockDriverState *bs)
 {
     if (!bdrv_is_inserted(bs) || bdrv_is_read_only(bs)) {
         return false;
@@ -518,6 +518,7 @@ bool bdrv_all_can_snapshot(bool has_devices, strList *devices,
     GList *iterbdrvs;
 
     GLOBAL_STATE_CODE();
+    GRAPH_RDLOCK_GUARD_MAINLOOP();
 
     if (bdrv_all_get_snapshot_devices(has_devices, devices, &bdrvs, errp) < 0) {
         return false;
@@ -554,6 +555,7 @@ int bdrv_all_delete_snapshot(const char *name,
     GList *iterbdrvs;
 
     GLOBAL_STATE_CODE();
+    GRAPH_RDLOCK_GUARD_MAINLOOP();
 
     if (bdrv_all_get_snapshot_devices(has_devices, devices, &bdrvs, errp) < 0) {
         return -1;
@@ -595,6 +597,7 @@ int bdrv_all_goto_snapshot(const char *name,
     GList *iterbdrvs;
 
     GLOBAL_STATE_CODE();
+    GRAPH_RDLOCK_GUARD_MAINLOOP();
 
     if (bdrv_all_get_snapshot_devices(has_devices, devices, &bdrvs, errp) < 0) {
         return -1;
@@ -631,6 +634,7 @@ int bdrv_all_has_snapshot(const char *name,
     GList *iterbdrvs;
 
     GLOBAL_STATE_CODE();
+    GRAPH_RDLOCK_GUARD_MAINLOOP();
 
     if (bdrv_all_get_snapshot_devices(has_devices, devices, &bdrvs, errp) < 0) {
         return -1;
@@ -673,7 +677,9 @@ int bdrv_all_create_snapshot(QEMUSnapshotInfo *sn,
 {
     g_autoptr(GList) bdrvs = NULL;
     GList *iterbdrvs;
+
     GLOBAL_STATE_CODE();
+    GRAPH_RDLOCK_GUARD_MAINLOOP();
 
     if (bdrv_all_get_snapshot_devices(has_devices, devices, &bdrvs, errp) < 0) {
         return -1;
@@ -715,6 +721,7 @@ BlockDriverState *bdrv_all_find_vmstate_bs(const char *vmstate_bs,
     GList *iterbdrvs;
 
     GLOBAL_STATE_CODE();
+    GRAPH_RDLOCK_GUARD_MAINLOOP();
 
     if (bdrv_all_get_snapshot_devices(has_devices, devices, &bdrvs, errp) < 0) {
         return NULL;