On Tue, May 19, 2020 at 06:11:38PM +0100, Stefan Hajnoczi wrote:
> QEMU block drivers are supposed to support aio_poll() from I/O
> completion callback functions. This means completion processing must be
> re-entrant.
> 
> The standard approach is to schedule a BH during completion processing
> and cancel it at the end of processing. If aio_poll() is invoked by a
> callback function then the BH will run. The BH continues the suspended
> completion processing.
> 
> All of this means that request A's cb() can synchronously wait for
> request B to complete. Previously the nvme block driver would hang
> because it didn't process completions from nested aio_poll().
> 
> Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
> ---
>  block/nvme.c       | 67 ++++++++++++++++++++++++++++++++++++++++------
>  block/trace-events |  2 +-
>  2 files changed, 60 insertions(+), 9 deletions(-)

Reviewed-by: Sergio Lopez <slp@redhat.com>