block: Protect bs->backing with graph_lock

Almost all functions that access bs->backing already take the graph
lock now. Add locking to the remaining users and finally annotate the
struct field itself as protected by the graph lock.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Message-ID: <20231027155333.420094-18-kwolf@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

9 files changed, 70 insertions, 27 deletions

diff --git a/block.c b/block.c
index cac517ab8b..ed0afdffbd 100644
--- a/block.c
+++ b/block.c
@@ -3560,10 +3560,14 @@ out:
 int bdrv_set_backing_hd(BlockDriverState *bs, BlockDriverState *backing_hd,
                         Error **errp)
 {
-    BlockDriverState *drain_bs = bs->backing ? bs->backing->bs : bs;
+    BlockDriverState *drain_bs;
     int ret;
     GLOBAL_STATE_CODE();
 
+    bdrv_graph_rdlock_main_loop();
+    drain_bs = bs->backing ? bs->backing->bs : bs;
+    bdrv_graph_rdunlock_main_loop();
+
     bdrv_ref(drain_bs);
     bdrv_drained_begin(drain_bs);
     bdrv_graph_wrlock(backing_hd);
@@ -3602,6 +3606,7 @@ int bdrv_open_backing_file(BlockDriverState *bs, QDict *parent_options,
     Error *local_err = NULL;
 
     GLOBAL_STATE_CODE();
+    GRAPH_RDLOCK_GUARD_MAINLOOP();
 
     if (bs->backing != NULL) {
         goto free_exit;
@@ -3643,10 +3648,7 @@ int bdrv_open_backing_file(BlockDriverState *bs, QDict *parent_options,
             implicit_backing = !strcmp(bs->auto_backing_file, bs->backing_file);
         }
 
-        bdrv_graph_rdlock_main_loop();
         backing_filename = bdrv_get_full_backing_filename(bs, &local_err);
-        bdrv_graph_rdunlock_main_loop();
-
         if (local_err) {
             ret = -EINVAL;
             error_propagate(errp, local_err);
@@ -3677,9 +3679,7 @@ int bdrv_open_backing_file(BlockDriverState *bs, QDict *parent_options,
     }
 
     if (implicit_backing) {
-        bdrv_graph_rdlock_main_loop();
         bdrv_refresh_filename(backing_hd);
-        bdrv_graph_rdunlock_main_loop();
         pstrcpy(bs->auto_backing_file, sizeof(bs->auto_backing_file),
                 backing_hd->filename);
     }
@@ -4750,8 +4750,8 @@ bdrv_reopen_parse_file_or_backing(BDRVReopenState *reopen_state,
 {
     BlockDriverState *bs = reopen_state->bs;
     BlockDriverState *new_child_bs;
-    BlockDriverState *old_child_bs = is_backing ? child_bs(bs->backing) :
-                                                  child_bs(bs->file);
+    BlockDriverState *old_child_bs;
+
     const char *child_name = is_backing ? "backing" : "file";
     QObject *value;
     const char *str;
@@ -4797,6 +4797,7 @@ bdrv_reopen_parse_file_or_backing(BDRVReopenState *reopen_state,
         g_assert_not_reached();
     }
 
+    old_child_bs = is_backing ? child_bs(bs->backing) : child_bs(bs->file);
     if (old_child_bs == new_child_bs) {
         ret = 0;
         goto out_rdlock;
@@ -5008,13 +5009,16 @@ bdrv_reopen_prepare(BDRVReopenState *reopen_state, BlockReopenQueue *queue,
      * file or if the image file has a backing file name as part of
      * its metadata. Otherwise the 'backing' option can be omitted.
      */
+    bdrv_graph_rdlock_main_loop();
     if (drv->supports_backing && reopen_state->backing_missing &&
         (reopen_state->bs->backing || reopen_state->bs->backing_file[0])) {
         error_setg(errp, "backing is missing for '%s'",
                    reopen_state->bs->node_name);
+        bdrv_graph_rdunlock_main_loop();
         ret = -EINVAL;
         goto error;
     }
+    bdrv_graph_rdunlock_main_loop();
 
     /*
      * Allow changing the 'backing' option. The new value can be
@@ -5204,10 +5208,11 @@ static void bdrv_close(BlockDriverState *bs)
     QLIST_FOREACH_SAFE(child, &bs->children, next, next) {
         bdrv_unref_child(bs, child);
     }
-    bdrv_graph_wrunlock();
 
     assert(!bs->backing);
     assert(!bs->file);
+    bdrv_graph_wrunlock();
+
     g_free(bs->opaque);
     bs->opaque = NULL;
     qatomic_set(&bs->copy_on_read, 0);
@@ -5531,7 +5536,9 @@ int bdrv_append(BlockDriverState *bs_new, BlockDriverState *bs_top,
 
     GLOBAL_STATE_CODE();
 
+    bdrv_graph_rdlock_main_loop();
     assert(!bs_new->backing);
+    bdrv_graph_rdunlock_main_loop();
 
     old_context = bdrv_get_aio_context(bs_top);
     bdrv_drained_begin(bs_top);
@@ -8115,7 +8122,7 @@ static bool append_strong_runtime_options(QDict *d, BlockDriverState *bs)
 /* Note: This function may return false positives; it may return true
  * even if opening the backing file specified by bs's image header
  * would result in exactly bs->backing. */
-static bool bdrv_backing_overridden(BlockDriverState *bs)
+static bool GRAPH_RDLOCK bdrv_backing_overridden(BlockDriverState *bs)
 {
     GLOBAL_STATE_CODE();
     if (bs->backing) {
diff --git a/block/commit.c b/block/commit.c
index 30bc082edc..eb3dc01f45 100644
--- a/block/commit.c
+++ b/block/commit.c
@@ -95,7 +95,10 @@ static void commit_abort(Job *job)
      * XXX Can (or should) we somehow keep 'consistent read' blocked even
      * after the failed/cancelled commit job is gone? If we already wrote
      * something to base, the intermediate images aren't valid any more. */
+    bdrv_graph_rdlock_main_loop();
     commit_top_backing_bs = s->commit_top_bs->backing->bs;
+    bdrv_graph_rdunlock_main_loop();
+
     bdrv_drained_begin(commit_top_backing_bs);
     bdrv_graph_wrlock(commit_top_backing_bs);
     bdrv_replace_node(s->commit_top_bs, commit_top_backing_bs, &error_abort);
@@ -219,7 +222,7 @@ bdrv_commit_top_preadv(BlockDriverState *bs, int64_t offset, int64_t bytes,
     return bdrv_co_preadv(bs->backing, offset, bytes, qiov, flags);
 }
 
-static void bdrv_commit_top_refresh_filename(BlockDriverState *bs)
+static GRAPH_RDLOCK void bdrv_commit_top_refresh_filename(BlockDriverState *bs)
 {
     pstrcpy(bs->exact_filename, sizeof(bs->exact_filename),
             bs->backing->bs->filename);
diff --git a/block/mirror.c b/block/mirror.c
index dfc1c416e8..2096fade90 100644
--- a/block/mirror.c
+++ b/block/mirror.c
@@ -479,7 +479,7 @@ static unsigned mirror_perform(MirrorBlockJob *s, int64_t offset,
     return bytes_handled;
 }
 
-static void coroutine_fn mirror_iteration(MirrorBlockJob *s)
+static void coroutine_fn GRAPH_RDLOCK mirror_iteration(MirrorBlockJob *s)
 {
     BlockDriverState *source = s->mirror_top_bs->backing->bs;
     MirrorOp *pseudo_op;
@@ -839,14 +839,18 @@ static void coroutine_fn mirror_throttle(MirrorBlockJob *s)
     }
 }
 
-static int coroutine_fn mirror_dirty_init(MirrorBlockJob *s)
+static int coroutine_fn GRAPH_UNLOCKED mirror_dirty_init(MirrorBlockJob *s)
 {
     int64_t offset;
-    BlockDriverState *bs = s->mirror_top_bs->backing->bs;
+    BlockDriverState *bs;
     BlockDriverState *target_bs = blk_bs(s->target);
     int ret;
     int64_t count;
 
+    bdrv_graph_co_rdlock();
+    bs = s->mirror_top_bs->backing->bs;
+    bdrv_graph_co_rdunlock();
+
     if (s->zero_target) {
         if (!bdrv_can_write_zeroes_with_unmap(target_bs)) {
             bdrv_set_dirty_bitmap(s->dirty_bitmap, 0, s->bdev_length);
@@ -926,7 +930,7 @@ static int coroutine_fn mirror_flush(MirrorBlockJob *s)
 static int coroutine_fn mirror_run(Job *job, Error **errp)
 {
     MirrorBlockJob *s = container_of(job, MirrorBlockJob, common.job);
-    BlockDriverState *bs = s->mirror_top_bs->backing->bs;
+    BlockDriverState *bs;
     MirrorBDSOpaque *mirror_top_opaque = s->mirror_top_bs->opaque;
     BlockDriverState *target_bs = blk_bs(s->target);
     bool need_drain = true;
@@ -938,6 +942,10 @@ static int coroutine_fn mirror_run(Job *job, Error **errp)
                                  checking for a NULL string */
     int ret = 0;
 
+    bdrv_graph_co_rdlock();
+    bs = bdrv_filter_bs(s->mirror_top_bs);
+    bdrv_graph_co_rdunlock();
+
     if (job_is_cancelled(&s->common.job)) {
         goto immediate_exit;
     }
@@ -1070,7 +1078,9 @@ static int coroutine_fn mirror_run(Job *job, Error **errp)
                 mirror_wait_for_free_in_flight_slot(s);
                 continue;
             } else if (cnt != 0) {
+                bdrv_graph_co_rdlock();
                 mirror_iteration(s);
+                bdrv_graph_co_rdunlock();
             }
         }
 
@@ -1640,7 +1650,7 @@ bdrv_mirror_top_pdiscard(BlockDriverState *bs, int64_t offset, int64_t bytes)
                                     offset, bytes, NULL, 0);
 }
 
-static void bdrv_mirror_top_refresh_filename(BlockDriverState *bs)
+static void GRAPH_RDLOCK bdrv_mirror_top_refresh_filename(BlockDriverState *bs)
 {
     if (bs->backing == NULL) {
         /* we can be here after failed bdrv_attach_child in
diff --git a/block/qed.c b/block/qed.c
index 45ae320290..686ad711f7 100644
--- a/block/qed.c
+++ b/block/qed.c
@@ -1138,7 +1138,7 @@ out:
 /**
  * Check if the QED_F_NEED_CHECK bit should be set during allocating write
  */
-static bool qed_should_set_need_check(BDRVQEDState *s)
+static bool GRAPH_RDLOCK qed_should_set_need_check(BDRVQEDState *s)
 {
     /* The flush before L2 update path ensures consistency */
     if (s->bs->backing) {
diff --git a/block/replication.c b/block/replication.c
index d522c7396f..49ecc608b2 100644
--- a/block/replication.c
+++ b/block/replication.c
@@ -363,6 +363,9 @@ static void reopen_backing_file(BlockDriverState *bs, bool writable,
     BdrvChild *hidden_disk, *secondary_disk;
     BlockReopenQueue *reopen_queue = NULL;
 
+    GLOBAL_STATE_CODE();
+    GRAPH_RDLOCK_GUARD_MAINLOOP();
+
     /*
      * s->hidden_disk and s->secondary_disk may not be set yet, as they will
      * only be set after the children are writable.
@@ -496,9 +499,11 @@ static void replication_start(ReplicationState *rs, ReplicationMode mode,
     case REPLICATION_MODE_PRIMARY:
         break;
     case REPLICATION_MODE_SECONDARY:
+        bdrv_graph_rdlock_main_loop();
         active_disk = bs->file;
         if (!active_disk || !active_disk->bs || !active_disk->bs->backing) {
             error_setg(errp, "Active disk doesn't have backing file");
+            bdrv_graph_rdunlock_main_loop();
             aio_context_release(aio_context);
             return;
         }
@@ -506,11 +511,11 @@ static void replication_start(ReplicationState *rs, ReplicationMode mode,
         hidden_disk = active_disk->bs->backing;
         if (!hidden_disk->bs || !hidden_disk->bs->backing) {
             error_setg(errp, "Hidden disk doesn't have backing file");
+            bdrv_graph_rdunlock_main_loop();
             aio_context_release(aio_context);
             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");
diff --git a/block/vmdk.c b/block/vmdk.c
index 91ed7a8d93..5c789bb65b 100644
--- a/block/vmdk.c
+++ b/block/vmdk.c
@@ -380,7 +380,7 @@ out:
     return ret;
 }
 
-static int coroutine_fn vmdk_is_cid_valid(BlockDriverState *bs)
+static int coroutine_fn GRAPH_RDLOCK vmdk_is_cid_valid(BlockDriverState *bs)
 {
     BDRVVmdkState *s = bs->opaque;
     uint32_t cur_pcid;
@@ -3044,8 +3044,9 @@ vmdk_co_get_info(BlockDriverState *bs, BlockDriverInfo *bdi)
     return 0;
 }
 
-static void vmdk_gather_child_options(BlockDriverState *bs, QDict *target,
-                                      bool backing_overridden)
+static void GRAPH_RDLOCK
+vmdk_gather_child_options(BlockDriverState *bs, QDict *target,
+                          bool backing_overridden)
 {
     /* No children but file and backing can be explicitly specified (TODO) */
     qdict_put(target, "file",
diff --git a/include/block/block_int-common.h b/include/block/block_int-common.h
index c0db862de7..ed6066929a 100644
--- a/include/block/block_int-common.h
+++ b/include/block/block_int-common.h
@@ -1178,7 +1178,7 @@ struct BlockDriverState {
      * are connected with BdrvChildRole.
      */
     QLIST_HEAD(, BdrvChild GRAPH_RDLOCK_PTR) children;
-    BdrvChild *backing;
+    BdrvChild * GRAPH_RDLOCK_PTR backing;
     BdrvChild *file;
 
     QLIST_HEAD(, BdrvChild GRAPH_RDLOCK_PTR) parents;
diff --git a/tests/unit/test-bdrv-drain.c b/tests/unit/test-bdrv-drain.c
index b16f831c23..ba4e42b197 100644
--- a/tests/unit/test-bdrv-drain.c
+++ b/tests/unit/test-bdrv-drain.c
@@ -218,8 +218,14 @@ static void do_drain_end_unlocked(enum drain_type drain_type, BlockDriverState *
     }
 }
 
-static void test_drv_cb_common(BlockBackend *blk, enum drain_type drain_type,
-                               bool recursive)
+/*
+ * Locking the block graph would be a bit cumbersome here because this function
+ * is called both in coroutine and non-coroutine context. We know this is a test
+ * and nothing else is running, so don't bother with TSA.
+ */
+static void coroutine_mixed_fn TSA_NO_TSA
+test_drv_cb_common(BlockBackend *blk, enum drain_type drain_type,
+                   bool recursive)
 {
     BlockDriverState *bs = blk_bs(blk);
     BlockDriverState *backing = bs->backing->bs;
@@ -307,8 +313,14 @@ static void test_drv_cb_co_drain(void)
     blk_unref(blk);
 }
 
-static void test_quiesce_common(BlockBackend *blk, enum drain_type drain_type,
-                                bool recursive)
+/*
+ * Locking the block graph would be a bit cumbersome here because this function
+ * is called both in coroutine and non-coroutine context. We know this is a test
+ * and nothing else is running, so don't bother with TSA.
+ */
+static void coroutine_mixed_fn TSA_NO_TSA
+test_quiesce_common(BlockBackend *blk, enum drain_type drain_type,
+                    bool recursive)
 {
     BlockDriverState *bs = blk_bs(blk);
     BlockDriverState *backing = bs->backing->bs;
@@ -1868,6 +1880,8 @@ static void bdrv_replace_test_drain_end(BlockDriverState *bs)
 {
     BDRVReplaceTestState *s = bs->opaque;
 
+    GRAPH_RDLOCK_GUARD_MAINLOOP();
+
     if (!s->setup_completed) {
         return;
     }
diff --git a/tests/unit/test-bdrv-graph-mod.c b/tests/unit/test-bdrv-graph-mod.c
index 22d4cd83f6..878544dbd5 100644
--- a/tests/unit/test-bdrv-graph-mod.c
+++ b/tests/unit/test-bdrv-graph-mod.c
@@ -206,15 +206,18 @@ static void test_should_update_child(void)
 
     bdrv_set_backing_hd(target, bs, &error_abort);
 
-    g_assert(target->backing->bs == bs);
     bdrv_graph_wrlock(NULL);
+    g_assert(target->backing->bs == bs);
     bdrv_attach_child(filter, target, "target", &child_of_bds,
                       BDRV_CHILD_DATA, &error_abort);
     bdrv_graph_wrunlock();
     aio_context_acquire(qemu_get_aio_context());
     bdrv_append(filter, bs, &error_abort);
     aio_context_release(qemu_get_aio_context());
+
+    bdrv_graph_rdlock_main_loop();
     g_assert(target->backing->bs == bs);
+    bdrv_graph_rdunlock_main_loop();
 
     bdrv_unref(filter);
     bdrv_unref(bs);