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    SubjectRe: [RFC][PATCH 0/9] Network receive deadlock prevention for NBD
    Evgeniy Polyakov wrote:
    > On Sun, Aug 13, 2006 at 01:16:15PM -0700, Daniel Phillips ( wrote:
    >>Indeed. The rest of the corner cases like netfilter, layered protocol and
    >>so on need to be handled, however they do not need to be handled right now
    >>in order to make remote storage on a lan work properly. The sane thing for
    >>the immediate future is to flag each socket as safe for remote block IO or
    >>not, then gradually widen the scope of what is safe. We need to set up an
    >>opt in strategy for network block IO that views such network subsystems as
    >>ipfilter as not safe by default, until somebody puts in the work to make
    >>them safe.
    > Just for clarification - it will be completely impossible to login using
    > openssh or some other priveledge separation protocol to the machine due
    > to the nature of unix sockets. So you will be unable to manage your
    > storage system just because it is in OOM - it is not what is expected
    > from reliable system.

    The system is not OOM, it is in reclaim, a transient condition that will be
    resolved in normal course by IO progress. However you raise an excellent
    point: if there is any remote management that we absolutely require to be
    available while remote IO is interrupted - manual failover for example -
    then we must supply a means of carrying out such remote administration, that
    is guaranteed not to deadlock on a normal mode memory request. This ends up
    as a new network stack feature I think, and probably a theoretical one for
    the time being since we don't actually know of any such mandatory login
    that must be carried out while remote disk IO is suspended.

    >>But really, if you expect to run reliable block IO to Zanzibar over an ssh
    >>tunnel through a firewall, then you might also consider taking up bungie
    >>jumping with the cord tied to your neck.
    > Just pure openssh for control connection (admin should be able to
    > login).

    And the admin will be able to, but in the cluster stack itself we don't
    bless such stupidity as emailing an admin to ask for a login in order to
    break a tie over which node should take charge of DLM recovery.


    Da niel
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