block: Mark bdrv_unref_child() GRAPH_WRLOCK

Instead of taking the writer lock internally, require callers to already
hold it when calling bdrv_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: <20230911094620.45040-21-kwolf@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

block.c

@@ -1701,7 +1701,9 @@ bdrv_open_driver(BlockDriverState *bs, BlockDriver *drv, const char *node_name,
 open_failed:
     bs->drv = NULL;
     if (bs->file != NULL) {
+        bdrv_graph_wrlock(NULL);
         bdrv_unref_child(bs, bs->file);
+        bdrv_graph_wrunlock();
         assert(!bs->file);
     }
     g_free(bs->opaque);
@@ -3331,8 +3333,9 @@ static void bdrv_set_inherits_from(BlockDriverState *bs,
  * @root that point to @root, where necessary.
  * @tran is allowed to be NULL. In this case no rollback is possible
  */
-static void bdrv_unset_inherits_from(BlockDriverState *root, BdrvChild *child,
-                                     Transaction *tran)
+static void GRAPH_WRLOCK
+bdrv_unset_inherits_from(BlockDriverState *root, BdrvChild *child,
+                         Transaction *tran)
 {
     BdrvChild *c;
 
@@ -3364,10 +3367,8 @@ 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();
 }
 
 
@@ -5164,9 +5165,11 @@ static void bdrv_close(BlockDriverState *bs)
         bs->drv = NULL;
     }
 
+    bdrv_graph_wrlock(NULL);
     QLIST_FOREACH_SAFE(child, &bs->children, next, next) {
         bdrv_unref_child(bs, child);
     }
+    bdrv_graph_wrunlock();
 
     assert(!bs->backing);
     assert(!bs->file);

block/blklogwrites.c

@@ -251,7 +251,9 @@ static int blk_log_writes_open(BlockDriverState *bs, QDict *options, int flags,
     ret = 0;
 fail_log:
     if (ret < 0) {
+        bdrv_graph_wrlock(NULL);
         bdrv_unref_child(bs, s->log_file);
+        bdrv_graph_wrunlock();
         s->log_file = NULL;
     }
 fail:
@@ -263,8 +265,10 @@ static void blk_log_writes_close(BlockDriverState *bs)
 {
     BDRVBlkLogWritesState *s = bs->opaque;
 
+    bdrv_graph_wrlock(NULL);
     bdrv_unref_child(bs, s->log_file);
     s->log_file = NULL;
+    bdrv_graph_wrunlock();
 }
 
 static int64_t coroutine_fn GRAPH_RDLOCK

block/blkverify.c

@@ -151,8 +151,10 @@ static void blkverify_close(BlockDriverState *bs)
 {
     BDRVBlkverifyState *s = bs->opaque;
 
+    bdrv_graph_wrlock(NULL);
     bdrv_unref_child(bs, s->test_file);
     s->test_file = NULL;
+    bdrv_graph_wrunlock();
 }
 
 static int64_t coroutine_fn GRAPH_RDLOCK

block/qcow2.c

@@ -1880,7 +1880,7 @@ qcow2_do_open(BlockDriverState *bs, QDict *options, int flags,
     g_free(s->image_data_file);
     if (open_data_file && has_data_file(bs)) {
         bdrv_graph_co_rdunlock();
-        bdrv_unref_child(bs, s->data_file);
+        bdrv_co_unref_child(bs, s->data_file);
         bdrv_graph_co_rdlock();
         s->data_file = NULL;
     }
@@ -2790,7 +2790,9 @@ static void qcow2_do_close(BlockDriverState *bs, bool close_data_file)
     g_free(s->image_backing_format);
 
     if (close_data_file && has_data_file(bs)) {
+        bdrv_graph_wrlock(NULL);
         bdrv_unref_child(bs, s->data_file);
+        bdrv_graph_wrunlock();
         s->data_file = NULL;
     }
 

block/quorum.c

@@ -1037,12 +1037,14 @@ static int quorum_open(BlockDriverState *bs, QDict *options, int flags,
 
 close_exit:
     /* cleanup on error */
+    bdrv_graph_wrlock(NULL);
     for (i = 0; i < s->num_children; i++) {
         if (!opened[i]) {
             continue;
         }
         bdrv_unref_child(bs, s->children[i]);
     }
+    bdrv_graph_wrunlock();
     g_free(s->children);
     g_free(opened);
 exit:
@@ -1055,9 +1057,11 @@ static void quorum_close(BlockDriverState *bs)
     BDRVQuorumState *s = bs->opaque;
     int i;
 
+    bdrv_graph_wrlock(NULL);
     for (i = 0; i < s->num_children; i++) {
         bdrv_unref_child(bs, s->children[i]);
     }
+    bdrv_graph_wrunlock();
 
     g_free(s->children);
 }
@@ -1147,7 +1151,9 @@ static void quorum_del_child(BlockDriverState *bs, BdrvChild *child,
     memmove(&s->children[i], &s->children[i + 1],
             (s->num_children - i - 1) * sizeof(BdrvChild *));
     s->children = g_renew(BdrvChild *, s->children, --s->num_children);
+    bdrv_graph_wrlock(NULL);
     bdrv_unref_child(bs, child);
+    bdrv_graph_wrunlock();
 
     quorum_refresh_flags(bs);
     bdrv_drained_end(bs);

block/replication.c

@@ -672,10 +672,13 @@ static void replication_done(void *opaque, int ret)
     if (ret == 0) {
         s->stage = BLOCK_REPLICATION_DONE;
 
+        bdrv_graph_wrlock(NULL);
         bdrv_unref_child(bs, s->secondary_disk);
         s->secondary_disk = NULL;
         bdrv_unref_child(bs, s->hidden_disk);
         s->hidden_disk = NULL;
+        bdrv_graph_wrunlock();
+
         s->error = 0;
     } else {
         s->stage = BLOCK_REPLICATION_FAILOVER_FAILED;

block/snapshot.c

@@ -281,7 +281,9 @@ int bdrv_snapshot_goto(BlockDriverState *bs,
         }
 
         /* .bdrv_open() will re-attach it */
+        bdrv_graph_wrlock(NULL);
         bdrv_unref_child(bs, fallback);
+        bdrv_graph_wrunlock();
 
         ret = bdrv_snapshot_goto(fallback_bs, snapshot_id, errp);
         open_ret = drv->bdrv_open(bs, options, bs->open_flags, &local_err);

block/vmdk.c

@@ -272,6 +272,7 @@ static void vmdk_free_extents(BlockDriverState *bs)
     BDRVVmdkState *s = bs->opaque;
     VmdkExtent *e;
 
+    bdrv_graph_wrlock(NULL);
     for (i = 0; i < s->num_extents; i++) {
         e = &s->extents[i];
         g_free(e->l1_table);
@@ -282,6 +283,8 @@ static void vmdk_free_extents(BlockDriverState *bs)
             bdrv_unref_child(bs, e->file);
         }
     }
+    bdrv_graph_wrunlock();
+
     g_free(s->extents);
 }
 
@@ -1220,7 +1223,9 @@ static int vmdk_parse_extents(const char *desc, BlockDriverState *bs,
             ret = vmdk_add_extent(bs, extent_file, true, sectors,
                             0, 0, 0, 0, 0, &extent, errp);
             if (ret < 0) {
+                bdrv_graph_wrlock(NULL);
                 bdrv_unref_child(bs, extent_file);
+                bdrv_graph_wrunlock();
                 goto out;
             }
             extent->flat_start_offset = flat_offset << 9;
@@ -1235,20 +1240,26 @@ static int vmdk_parse_extents(const char *desc, BlockDriverState *bs,
             }
             g_free(buf);
             if (ret) {
+                bdrv_graph_wrlock(NULL);
                 bdrv_unref_child(bs, extent_file);
+                bdrv_graph_wrunlock();
                 goto out;
             }
             extent = &s->extents[s->num_extents - 1];
         } else if (!strcmp(type, "SESPARSE")) {
             ret = vmdk_open_se_sparse(bs, extent_file, bs->open_flags, errp);
             if (ret) {
+                bdrv_graph_wrlock(NULL);
                 bdrv_unref_child(bs, extent_file);
+                bdrv_graph_wrunlock();
                 goto out;
             }
             extent = &s->extents[s->num_extents - 1];
         } else {
             error_setg(errp, "Unsupported extent type '%s'", type);
+            bdrv_graph_wrlock(NULL);
             bdrv_unref_child(bs, extent_file);
+            bdrv_graph_wrunlock();
             ret = -ENOTSUP;
             goto out;
         }

include/block/block-global-state.h

@@ -225,7 +225,12 @@ void bdrv_ref(BlockDriverState *bs);
 void no_coroutine_fn bdrv_unref(BlockDriverState *bs);
 void coroutine_fn no_co_wrapper bdrv_co_unref(BlockDriverState *bs);
 void GRAPH_WRLOCK bdrv_schedule_unref(BlockDriverState *bs);
-void bdrv_unref_child(BlockDriverState *parent, BdrvChild *child);
+
+void GRAPH_WRLOCK
+bdrv_unref_child(BlockDriverState *parent, BdrvChild *child);
+
+void coroutine_fn no_co_wrapper_bdrv_wrlock
+bdrv_co_unref_child(BlockDriverState *parent, BdrvChild *child);
 
 BdrvChild * GRAPH_WRLOCK
 bdrv_attach_child(BlockDriverState *parent_bs,

tests/unit/test-bdrv-drain.c

@@ -967,9 +967,12 @@ typedef struct BDRVTestTopState {
 static void bdrv_test_top_close(BlockDriverState *bs)
 {
     BdrvChild *c, *next_c;
+
+    bdrv_graph_wrlock(NULL);
     QLIST_FOREACH_SAFE(c, &bs->children, next, next_c) {
         bdrv_unref_child(bs, c);
     }
+    bdrv_graph_wrunlock();
 }
 
 static int coroutine_fn GRAPH_RDLOCK
@@ -1024,7 +1027,7 @@ static void coroutine_fn test_co_delete_by_drain(void *opaque)
     } else {
         BdrvChild *c, *next_c;
         QLIST_FOREACH_SAFE(c, &bs->children, next, next_c) {
-            bdrv_unref_child(bs, c);
+            bdrv_co_unref_child(bs, c);
         }
     }
 
@@ -1162,10 +1165,11 @@ static void detach_indirect_bh(void *opaque)
     struct detach_by_parent_data *data = opaque;
 
     bdrv_dec_in_flight(data->child_b->bs);
+
+    bdrv_graph_wrlock(NULL);
     bdrv_unref_child(data->parent_b, data->child_b);
 
     bdrv_ref(data->c);
-    bdrv_graph_wrlock(NULL);
     data->child_c = bdrv_attach_child(data->parent_b, data->c, "PB-C",
                                       &child_of_bds, BDRV_CHILD_DATA,
                                       &error_abort);