Re: Network Stack Locking

From: Harti Brandt (harti_at_freebsd.org)
Date: 05/24/04

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    Date: Mon, 24 May 2004 11:08:13 +0200 (MET DST)
To: Robert Watson <rwatson@freebsd.org>

    On Thu, 20 May 2004, Robert Watson wrote:

    RW>- ATM -- Harti? :-)

    Sure. At least netnatm, netgraph/atm and the various drivers. At one
    point I want to get rid of netatm, so I don't want to put effort into
    netatm (just keep it working and compliling).

    netgraph/atm should be clean to the point as netgraph in general is clean
    (with regards to locking). The drivers (en, [pfh]atm) also are locked,
    but I'll probably do another iteration when I get my working environment
    back (I'm currently moving from Berlin to Munich).

    RW>- Network device drivers -- some have locking, some have correct locking,
    RW> some have potential interactions with other pieces of the system (such
    RW> as the USB stack). Note that for a driver to work correctly with a
    RW> Giant-free system, it must be safe to invoke ifp->if_start() without
    RW> holding Giant, and for if_start() to be aware that it cannot
    RW> acquire Giant without generating a lock order issue. It's OK for
    RW> if_input() to be called with Giant, although undesirable generally.
    RW> Some drivers also have locking that is commented out by default due to
    RW> use of recursive locks, but I'm not sure this is necessarily sufficient
    RW> problem not to just turn on the locking.

    Is there anybody working on the interaction between the network drivers
    and the module loader (race condition between the interrupt handler and
    xxx_detach())?

    harti
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