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    SubjectRe: Kernel 3.4.X NFS server regression
    On 06/11/2012 05:11 PM, Jeff Layton wrote:

    > On Mon, 11 Jun 2012 17:05:28 +0300
    > Boaz Harrosh <bharrosh@panasas.com> wrote:
    >
    >> On 06/11/2012 04:51 PM, Jeff Layton wrote:
    >>
    >>>
    >>> That was considered here, but the problem with the usermode helper is
    >>> that you can't pass anything back to the kernel but a simple status
    >>> code (and that's assuming that you wait for it to exit). In the near
    >>> future, we'll need to pass back more info to the kernel for this, so
    >>> the usermode helper callout wasn't suitable.
    >>>
    >>
    >>
    >> I have answered that in my mail. Repeated here again. Well you made
    >> a simple mistake. Because it is *easy* to pass back any number and
    >> size of information from user-mode.
    >>
    >> You just setup a sysfs entry points where the answers are written
    >> back to. It's an easy trick to setup a thread safe, way with a
    >> cookie but 90% of the time you don't have to. Say you set up
    >> a structure of per-client (identified uniquely) then user mode
    >> answers back per client, concurrency will not do any harm, since
    >> you answer to the same question the same answer. ans so on. Each
    >> problem it's own.
    >>
    >> If you want we can talk about this, it would be easy for me to setup
    >> a toll free conference number we can all use.
    >
    > That helpful advice would have been welcome about 3-4 months ago when I
    > first proposed this in detail. At that point you're working with
    > multiple upcall/downcall mechanisms, which was something I was keen to
    > avoid.
    >
    > I'm not opposed to moving in that direction, but it basically means
    > you're going to rip out everything I've got here so far and replace it.
    >
    > If you're willing to do that work, I'll be happy to work with you on
    > it, but I don't have the time or inclination to do that on my own right
    > now.
    >


    No such luck. sorry. I wish I could, but coming from a competing server
    company, you can imagine the priority of that ever happening.
    (Even though I use the Linux-Server everyday for my development and
    am putting lots of efforts into still, mainly in pnfs)

    Hopefully re-examining the code, it could all be salvaged just the
    same, only lots of code thrown a way.

    But mean-while please address my concern below:
    Boaz Harrosh wrote:

    > One more thing, the most important one. We have already fixed that in the
    > past and I was hoping the lesson was learned. Apparently it was not, and
    > we are doomed to do this mistake for ever!!
    >
    > What ever crap fails times out and crashes, in the recovery code, we don't
    > give a dam. It should never affect any Server-client communication.
    >
    > When the grace periods ends the clients gates opens period. *Any* error
    > return from state recovery code must be carefully ignored and normal
    > operations resumed. At most on error, we move into a mode where any
    > recovery request from client is accepted, since we don't have any better
    > data to verify it.
    >
    > Please comb recovery code to make sure any catastrophe is safely ignored.
    > We already did that before and it used to work.


    We should make sure that any state recovery code does not interfere with
    regular operations. and fails gracefully / shuts up.

    We used to have that, apparently it re-broke. Clients should always be granted
    access, after grace period. And Server should be made sure not to fail in any
    situation.

    I would look into it but I'm not uptodate anymore, I wish you or Bruce could.

    Thanks for your work so far, sorry to be bearer of bad news
    Boaz


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