Re: [PATCH 3/4] block/nbd: fix reconnect-delay

[Eric Blake]

On 9/3/20 2:03 PM, Vladimir Sementsov-Ogievskiy wrote:
> reconnect-delay has a design flaw: we handle it in the same loop where
> we do connection attempt. So, reconnect-delay may be exceeded by
> unpredictable time of connection attempt.
>
> Let's instead use separate timer.
>
> How to reproduce the bug:

> This will make the connect() call of qemu-io at node2 take a long time.
>
> And you'll see that read command in qemu-io will hang for a long time,
> more than 15 seconds specified by reconnect-delay parameter. It's the
> bug.
>
> 8. Don't forget to drop iptables rule on node1:
>
>     sudo iptables -D INPUT -p tcp --dport 10809 -j DROP
>
> Important note: Step [5] is necessary to reproduce _this_ bug. If we
> miss step [5], the read command (step 6) will hang for a long time and
> this commit doesn't help, because there will be not long connect() to
> unreachable host, but long sendmsg() to unreachable host, which should
> be fixed by enabling and adjusting keep-alive on the socket, which is a
> thing for further patch set.
>
> Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
> ---
>   block/nbd.c | 59 +++++++++++++++++++++++++++++++++++++++++++++--------
>   1 file changed, 50 insertions(+), 9 deletions(-)

Reviewed-by: Eric Blake <eblake@redhat.com>

--
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3226
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