do_drive_backup() acquires the AioContext lock of the corresponding
BlockDriverState. This is not a problem when it's called from
qmp_drive_backup(), but drive_backup_prepare() also acquires the lock
before calling it.

Additionally, Max Reitz pointed out that bdrv_try_set_aio_context() is
called at do_backup_common() with the new context held, and the old
context not held, while it expects it to be the other way
around. This is also the case for other uses of that function on
blockdev.c.

This patch series fixes all occurrences of bdrv_try_set_aio_context()
to honor the context requirements. It also changes
drive_backup_prepare() to release the context before calling
do_drive_backup().

---
Changelog

v2:
 - Honor bdrv_try_set_aio_context() context acquisition requirements
   (thanks Max Reitz).
 - Release the context at drive_backup_prepare() instead of avoiding
   re-acquiring it at do_drive_baclup(). (thanks Max Reitz)
 - Convert a single patch into a two-patch series.
---

Sergio Lopez (2):
  blockdev: release the AioContext at drive_backup_prepare
  blockdev: honor bdrv_try_set_aio_context() context requirements

 blockdev.c | 127 ++++++++++++++++++++++++++++++++---------------------
 1 file changed, 76 insertions(+), 51 deletions(-)

-- 
2.21.0