Re: Tracking down LORs

From: Roman Kurakin (rik_at_cronyx.ru)
Date: 08/20/04

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    Date: Fri, 20 Aug 2004 22:29:50 +0400
To: John Baldwin <jhb@FreeBSD.org>

    John Baldwin wrote:

    >On Friday 20 August 2004 04:08 am, Roman Kurakin wrote:
    >
    >
    >>Robert Watson wrote:
    >>
    >>
    >>>On Fri, 20 Aug 2004, Roman Kurakin wrote:
    >>>
    >>>
    >>>> Currently I am trying to track down a couple of LORS in my code.
    >>>>But it seems that I do not undestand smth or all things id realy so bad.
    >>>>
    >>>>
    >>>I find it's very helpful to add lock orders to the hard-coded lock order
    >>>table in subr_witness.c. Without hard-coded entries, WITNESS will
    >>>dynamically build an order based on observed lock use. This is generally
    >>>fine, but once in a while the "wrong" order will be used before the
    >>>"right" order, so the lock order warning will print for the "right" order,
    >>>leaving less useful debugging information. The table allows the
    >>>definition of partial orders, so you can specify relationships between
    >>>subsets of mutexes of interest. WITNESS will flesh out remaining orders
    >>>through dynamic discovery.
    >>>
    >>>
    >>I'll try to go this way, since I am in dead end.
    >>
    >>
    >
    >Note that some lock orders as also inferred via transitivity.
    >
    >For example, let's say you have three locks a, b, and c. One thread locks a
    >then b, so witness saves that order. A second thread locks b then c, so
    >witness saves that order. If a third thread tries to lock c then a, an LOR
    >will result. This is similar to how > is transitive, i.e. if a > b and b >
    >c, then a > c.
    >
    >
    It looks like I have smth like that. But I am get stuck with boot loader
    problem for now :-(
    I switched to that problem since that machine was the only that could
    work fast enough
    and has ISA slots.
    Than I get back to LOR problem and solve it, I guess I'll have to write
    some FAQ that
    will help to track down LORs.

    Thanks to all for replies! Now I have some ideas to move on.

    rik

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