Question about block graph lock limitation with generated co-wrappers

[Fiona Ebner]

Hi,
we have a custom block driver downstream, which currently calls
bdrv_get_info() (for its file child) in the bdrv_refresh_limits()
callback. However, with graph locking, this doesn't work anymore.
AFAICT, the reason is the following:

The block driver has a backing file option.
During initialization, in bdrv_set_backing_hd(), the graph lock is
acquired exclusively.
Then the bdrv_refresh_limits() callback is invoked.
Now bdrv_get_info() is called, which is a generated co-wrapper.
The bdrv_co_get_info_entry() function tries to acquire the graph lock
for reading, sees that has_writer is true and so the coroutine will be
put to wait, leading to a deadlock.

For my specific case, I can move the bdrv_get_info() call to bdrv_open()
as a workaround. But I wanted to ask if there is a way to make generated
co-wrappers inside an exclusively locked section work? And if not, could
we introduce/extend the annotations, so the compiler can catch this kind
of issue, i.e. calling a generated co-wrapper while in an exclusively
locked section?

Best Regards,
Fiona