Re: [PATCH v3 09/24] block: move drain outside of bdrv_try_change_aio_context()

[Kevin Wolf <kwolf@redhat.com>]

Am 26.05.2025 um 15:21 hat Fiona Ebner geschrieben:
> This is part of resolving the deadlock mentioned in commit "block:
> move draining out of bdrv_change_aio_context() and mark GRAPH_RDLOCK".
> 
> Convert the function to a _locked() version that has to be called with
> the graph lock held and add a convenience wrapper that has to be
> called with the graph unlocked, which drains and takes the lock
> itself. Since bdrv_try_change_aio_context() is global state code, the
> wrapper is too.
> 
> Callers are adapted to use the appropriate variant, depending on
> whether the caller already holds the lock. In the
> test_set_aio_context() unit test, prior drains can be removed, because
> draining already happens inside the new wrapper.
> 
> Note that bdrv_attach_child_common_abort(), bdrv_attach_child_common()
> and bdrv_root_unref_child() hold the graph lock and are not actually
> allowed to drain either. This will be addressed in the following
> commits.
> 
> Functions like qmp_blockdev_mirror() query the nodes to act on before
> draining and locking. In theory, draining could invalidate those nodes.
> This kind of issue is not addressed by these commits.
> 
> Signed-off-by: Fiona Ebner <f.ebner@proxmox.com>

Reviewed-by: Kevin Wolf <kwolf@redhat.com>