copy-before-write: Fix open with child in iothread

The AioContext lock must not be held for bdrv_open_child(), but it is
necessary for the following operations, in particular those using nested
event loops in coroutine wrappers.

Temporarily dropping the main AioContext lock is not necessary because
we know we run in the main thread.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Message-Id: <20230525124713.401149-9-kwolf@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

diff --git a/block/copy-before-write.c b/block/copy-before-write.c
index 646d8227a4616edb896b010ee3687f19df9ce37d..b866e42271d0c7553b6951da12b7d6d88f21de4a 100644 (file)
--- a/block/copy-before-write.c
+++ b/block/copy-before-write.c
@@ -412,6 +412,7 @@ static int cbw_open(BlockDriverState *bs, QDict *options, int flags,
     int64_t cluster_size;
     g_autoptr(BlockdevOptions) full_opts = NULL;
     BlockdevOptionsCbw *opts;
+    AioContext *ctx;
     int ret;
 
     full_opts = cbw_parse_options(options, errp);
@@ -432,11 +433,15 @@ static int cbw_open(BlockDriverState *bs, QDict *options, int flags,
         return -EINVAL;
     }
 
+    ctx = bdrv_get_aio_context(bs);
+    aio_context_acquire(ctx);
+
     if (opts->bitmap) {
         bitmap = block_dirty_bitmap_lookup(opts->bitmap->node,
                                            opts->bitmap->name, NULL, errp);
         if (!bitmap) {
-            return -EINVAL;
+            ret = -EINVAL;
+            goto out;
         }
     }
     s->on_cbw_error = opts->has_on_cbw_error ? opts->on_cbw_error :
@@ -454,21 +459,24 @@ static int cbw_open(BlockDriverState *bs, QDict *options, int flags,
     s->bcs = block_copy_state_new(bs->file, s->target, bitmap, errp);
     if (!s->bcs) {
         error_prepend(errp, "Cannot create block-copy-state: ");
-        return -EINVAL;
+        ret = -EINVAL;
+        goto out;
     }
 
     cluster_size = block_copy_cluster_size(s->bcs);
 
     s->done_bitmap = bdrv_create_dirty_bitmap(bs, cluster_size, NULL, errp);
     if (!s->done_bitmap) {
-        return -EINVAL;
+        ret = -EINVAL;
+        goto out;
     }
     bdrv_disable_dirty_bitmap(s->done_bitmap);
 
     /* s->access_bitmap starts equal to bcs bitmap */
     s->access_bitmap = bdrv_create_dirty_bitmap(bs, cluster_size, NULL, errp);
     if (!s->access_bitmap) {
-        return -EINVAL;
+        ret = -EINVAL;
+        goto out;
     }
     bdrv_disable_dirty_bitmap(s->access_bitmap);
     bdrv_dirty_bitmap_merge_internal(s->access_bitmap,
@@ -478,7 +486,10 @@ static int cbw_open(BlockDriverState *bs, QDict *options, int flags,
     qemu_co_mutex_init(&s->lock);
     QLIST_INIT(&s->frozen_read_reqs);
 
-    return 0;
+    ret = 0;
+out:
+    aio_context_release(ctx);
+    return ret;
 }
 
 static void cbw_close(BlockDriverState *bs)