CFR: bridge locking

From: Sam Leffler (sam_at_errno.com)
Date: 08/20/03

  • Next message: Sam Leffler: "CFR: ipfw locking" 
    Date: Wed, 20 Aug 2003 09:34:54 -0700
To: freebsd-net@freebsd.org, freebsd-arch@freebsd.org

    http://www.freebsd.org/~sam/bridge.patch

    This patch adds locking and also overhauls the bridge code some to do
    things like replace explicit numbers with #defines and cleanup the
    debugging code. I also restructured the forwarding code to avoid grabbing
    the ifnet lock if possible and optimized the common case of bridging two
    interfaces. There are a couple of LOR issues to be resolved before it can
    be committed. In particular the output path has a LOR that can deadlock.
    I'm making it available for review now in case folks have other comments.

    Beware that buried in these changes are a renaming of the bridge MIB
    variables to be under a net.link.ether.bridge. node. Those changes will
    not be carried over into the committed code unless folks are interested
    (since it'll break lots of rc scripts).

    Note that drivers that operate Giant-free with bridging need to release
    their "driver lock" before passing packets up. Otherwise the up call can
    result in an immediate return through the start method and deadlock (unless
    the lock is marked to allow recursion, which should be eliminated if at all
    possible). I've made these modifications for the em, wi, and sis drivers
    but have not committed them. The fxp driver already does this and the ath
    driver has a totally different locking strategy where this doesn't occur.
    Short term dropping the lock around the up call will work but is
    suboptimal. Long term we may want to revise the locking strategy for
    drivers to eliminate this issue. This will likely be revisited when I get
    to more performance tuning (unless someone else does it--hint hint).

    One other minor change: I moved the printf "BRIDGE 020214 loaded" under
    bootverbose. Can anyone tell me what 020214 means?

    This code has been in "production use" on my interior firewall (a soekris
    box) for a week. This box runs with the sis driver Giant-free.

            Sam

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