commit 9102f2ebdb71809af1c5ee4a4a255927e3dabca4
author Kevin Wolf <kwolf@redhat.com> Thu May 25 14:47:09 2023 +0200
committer Kevin Wolf <kwolf@redhat.com> Tue May 30 17:29:35 2023 +0200
tree f504a4d7d1055e6f7c1aaeee9e04a284b15f7b77
parent 6e0121593288252d9e62448578368678eea3446c

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>

block/copy-before-write.c

diff --git a/block/copy-before-write.c b/block/copy-before-write.c
index 646d822..b866e42 100644
--- a/block/copy-before-write.c
+++ b/block/copy-before-write.c
@@ -412,6 +412,7 @@
     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 @@
         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 @@
     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 @@
     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)