[PULL 43/51] block: Fix locking in external_snapshot_prepare()

[Kevin Wolf]

bdrv_img_create() polls internally (when calling bdrv_create(), which is
a co_wrapper), so it can't be called while holding the lock of any
AioContext except the current one without causing deadlocks. Drop the
lock around the call in external_snapshot_prepare().

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Message-Id: <20221207131838.239125-11-kwolf@redhat.com>
Reviewed-by: Emanuele Giuseppe Esposito <eesposit@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
---
 block.c    | 4 ++++
 blockdev.c | 4 ++++
 2 files changed, 8 insertions(+)

diff --git a/block.c b/block.c
index 6191ac1f44..44d59362d6 100644
--- a/block.c
+++ b/block.c
@@ -6924,6 +6924,10 @@ bool bdrv_op_blocker_is_empty(BlockDriverState *bs)
     return true;
 }
 
+/*
+ * Must not be called while holding the lock of an AioContext other than the
+ * current one.
+ */
 void bdrv_img_create(const char *filename, const char *fmt,
                      const char *base_filename, const char *base_fmt,
                      char *options, uint64_t img_size, int flags, bool quiet,
diff --git a/blockdev.c b/blockdev.c
index 8ffb3d9537..011e48df7b 100644
--- a/blockdev.c
+++ b/blockdev.c
@@ -1524,10 +1524,14 @@ static void external_snapshot_prepare(BlkActionState 
*common,
                 goto out;
             }
             bdrv_refresh_filename(state->old_bs);
+
+            aio_context_release(aio_context);
             bdrv_img_create(new_image_file, format,
                             state->old_bs->filename,
                             state->old_bs->drv->format_name,
                             NULL, size, flags, false, &local_err);
+            aio_context_acquire(aio_context);
+
             if (local_err) {
                 error_propagate(errp, local_err);
                 goto out;
-- 
2.38.1