block: Mark bdrv_apply_auto_read_only() and callers GRAPH_RDLOCK

This adds GRAPH_RDLOCK annotations to declare that callers of
bdrv_apply_auto_read_only() need to hold a reader lock for the graph
because it calls bdrv_can_set_read_only(), which indirectly accesses the
parents list of a node.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Message-ID: <20230929145157.45443-19-kwolf@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

block.c

@@ -320,8 +320,6 @@ int bdrv_apply_auto_read_only(BlockDriverState *bs, const char *errmsg,
     int ret = 0;
     IO_CODE();
 
-    assume_graph_lock(); /* FIXME */
-
     if (!(bs->open_flags & BDRV_O_RDWR)) {
         return 0;
     }
@@ -1908,7 +1906,9 @@ static int bdrv_open_common(BlockDriverState *bs, BlockBackend *file,
 
     if (use_bdrv_whitelist && !bdrv_is_whitelisted(drv, ro)) {
         if (!ro && bdrv_is_whitelisted(drv, true)) {
+            bdrv_graph_rdlock_main_loop();
             ret = bdrv_apply_auto_read_only(bs, NULL, NULL);
+            bdrv_graph_rdunlock_main_loop();
         } else {
             ret = -ENOTSUP;
         }

block/bochs.c

@@ -106,7 +106,9 @@ static int bochs_open(BlockDriverState *bs, QDict *options, int flags,
     int ret;
 
     /* No write support yet */
+    bdrv_graph_rdlock_main_loop();
     ret = bdrv_apply_auto_read_only(bs, NULL, errp);
+    bdrv_graph_rdunlock_main_loop();
     if (ret < 0) {
         return ret;
     }

block/cloop.c

@@ -67,7 +67,9 @@ static int cloop_open(BlockDriverState *bs, QDict *options, int flags,
     uint32_t offsets_size, max_compressed_block_size = 1, i;
     int ret;
 
+    bdrv_graph_rdlock_main_loop();
     ret = bdrv_apply_auto_read_only(bs, NULL, errp);
+    bdrv_graph_rdunlock_main_loop();
     if (ret < 0) {
         return ret;
     }

block/curl.c

@@ -696,8 +696,10 @@ static int curl_open(BlockDriverState *bs, QDict *options, int flags,
     const char *protocol_delimiter;
     int ret;
 
+    bdrv_graph_rdlock_main_loop();
     ret = bdrv_apply_auto_read_only(bs, "curl driver does not support writes",
                                     errp);
+    bdrv_graph_rdunlock_main_loop();
     if (ret < 0) {
         return ret;
     }

block/dmg.c

@@ -452,7 +452,9 @@ static int dmg_open(BlockDriverState *bs, QDict *options, int flags,
     int64_t offset;
     int ret;
 
+    bdrv_graph_rdlock_main_loop();
     ret = bdrv_apply_auto_read_only(bs, NULL, errp);
+    bdrv_graph_rdunlock_main_loop();
     if (ret < 0) {
         return ret;
     }

block/gluster.c

@@ -863,11 +863,13 @@ static int qemu_gluster_open(BlockDriverState *bs,  QDict *options,
     if (ret == -EACCES || ret == -EROFS) {
         /* Try to degrade to read-only, but if it doesn't work, still use the
          * normal error message. */
+        bdrv_graph_rdlock_main_loop();
         if (bdrv_apply_auto_read_only(bs, NULL, NULL) == 0) {
             open_flags = (open_flags & ~O_RDWR) | O_RDONLY;
             s->fd = glfs_open(s->glfs, gconf->path, open_flags);
             ret = s->fd ? 0 : -errno;
         }
+        bdrv_graph_rdunlock_main_loop();
     }
 
     s->supports_seek_data = qemu_gluster_test_seek(s->fd);

block/iscsi.c

@@ -1925,7 +1925,9 @@ static int iscsi_open(BlockDriverState *bs, QDict *options, int flags,
     /* Check the write protect flag of the LUN if we want to write */
     if (iscsilun->type == TYPE_DISK && (flags & BDRV_O_RDWR) &&
         iscsilun->write_protected) {
+        bdrv_graph_rdlock_main_loop();
         ret = bdrv_apply_auto_read_only(bs, "LUN is write protected", errp);
+        bdrv_graph_rdunlock_main_loop();
         if (ret < 0) {
             goto out;
         }

block/nbd.c

@@ -275,7 +275,8 @@ static bool nbd_client_will_reconnect(BDRVNBDState *s)
  * Return failure if the server's advertised options are incompatible with the
  * client's needs.
  */
-static int nbd_handle_updated_info(BlockDriverState *bs, Error **errp)
+static int coroutine_fn GRAPH_RDLOCK
+nbd_handle_updated_info(BlockDriverState *bs, Error **errp)
 {
     BDRVNBDState *s = (BDRVNBDState *)bs->opaque;
     int ret;

block/rbd.c

@@ -1168,7 +1168,9 @@ static int qemu_rbd_open(BlockDriverState *bs, QDict *options, int flags,
     /* If we are using an rbd snapshot, we must be r/o, otherwise
      * leave as-is */
     if (s->snap != NULL) {
+        bdrv_graph_rdlock_main_loop();
         r = bdrv_apply_auto_read_only(bs, "rbd snapshots are read-only", errp);
+        bdrv_graph_rdunlock_main_loop();
         if (r < 0) {
             goto failed_post_open;
         }

include/block/block-io.h

@@ -163,8 +163,10 @@ bdrv_is_allocated_above(BlockDriverState *bs, BlockDriverState *base,
 int coroutine_fn GRAPH_RDLOCK
 bdrv_co_is_zero_fast(BlockDriverState *bs, int64_t offset, int64_t bytes);
 
-int bdrv_apply_auto_read_only(BlockDriverState *bs, const char *errmsg,
-                              Error **errp);
+int GRAPH_RDLOCK
+bdrv_apply_auto_read_only(BlockDriverState *bs, const char *errmsg,
+                          Error **errp);
+
 bool bdrv_is_read_only(BlockDriverState *bs);
 bool bdrv_is_writable(BlockDriverState *bs);
 bool bdrv_is_sg(BlockDriverState *bs);