Re: [PATCH 0/7] block/nbd: decouple reconnect from drain

[Eric Blake <eblake@redhat.com>]

On 3/15/21 1:06 AM, Roman Kagan wrote:
> The reconnection logic doesn't need to stop while in a drained section.
> Moreover it has to be active during the drained section, as the requests
> that were caught in-flight with the connection to the server broken can
> only usefully get drained if the connection is restored.  Otherwise such
> requests can only either stall resulting in a deadlock (before
> 8c517de24a), or be aborted defeating the purpose of the reconnection
> machinery (after 8c517de24a).
> 
> This series aims to just stop messing with the drained section in the
> reconnection code.
> 
> While doing so it undoes the effect of 5ad81b4946 ("nbd: Restrict
> connection_co reentrance"); as I've missed the point of that commit I'd
> appreciate more scrutiny in this area.

Soft freeze is today.  I'm leaning towards declaring this series as a
bug fix (and so give it some more soak time to get right, but still okay
for -rc1) rather than a feature addition (and therefore would need to be
in a pull request today).  Speak up now if this characterization is off
base.

> 
> Roman Kagan (7):
>   block/nbd: avoid touching freed connect_thread
>   block/nbd: use uniformly nbd_client_connecting_wait
>   block/nbd: assert attach/detach runs in the proper context
>   block/nbd: transfer reconnection stuff across aio_context switch
>   block/nbd: better document a case in nbd_co_establish_connection
>   block/nbd: decouple reconnect from drain
>   block/nbd: stop manipulating in_flight counter
> 
>  block/nbd.c  | 191 +++++++++++++++++++++++----------------------------
>  nbd/client.c |   2 -
>  2 files changed, 86 insertions(+), 107 deletions(-)
> 

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3226
Virtualization:  qemu.org | libvirt.org