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    SubjectRe: [RFC][PATCH] pstore: Skip spinlock when just one cpu is online
    On Fri, Dec 07, 2012 at 11:43:03PM +0000, Seiji Aguchi wrote:
    > > Can all these things really happen (did you run into this problem on a real system?). Or is this just a theoretical problem. Ugly (but
    > > practical) hacks might be OK to solve real problems.
    >
    > It is a theoretical problem right now.
    > But it is a timing issue and there is a possibility to happen actually.
    >
    > > But do we really want them to fix problems that actually never happen?
    >
    > If we find a problem (even if it is theoretical), we can't say "It actually never happen.".
    >
    > I have some reasons to submit this patch before reproducing actually.
    >
    > 1)
    > It is too late if we fix a problem after it actually happened in case where we apply Linux, including pstore,
    > to mission critical systems, because the failure of those systems has a great impact on a whole society.
    > Customers in this area ask us to fix a problem as soon as possible.
    > On the other hand, this kind of timing issue is hard to reproduce.
    > So, our support service engineers often work all night to reproduce it.
    > It is a nightmare for us.
    >
    > If we can fix it with a small patch in adance, it is really helpful for us.

    As I said in my email I just sent, it may not help you without testing it.
    As there are probably other problems in that un-tested theoretical
    scenario.

    >
    > 2)
    > In the long term, I plan to add a kmsg_dump to a kexec path because kdump may fail in the real world.
    > In that case, we need another troubleshooting material like pstore to detect a root cause of failure.

    But you are assuming that kmsg_dump is perfect and it isn't, in which case
    by putting kmsg_dump in the kdump path, you actually may be blocking kdump
    from working.

    That is the biggest hold up for those guys from including it I believe.

    Cheers,
    Don


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