Re: SMP, DEVICE_POLLING and fxp LOR

From: Ruslan Ermilov (ru_at_FreeBSD.org)
Date: 05/30/05

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    Date: Mon, 30 May 2005 22:15:02 +0300
To: Ed Maste <emaste@phaedrus.sandvine.ca>

    On Mon, May 30, 2005 at 09:44:43AM -0400, Ed Maste wrote:
    > A few days ago I posted to -stable about a LOR observed on our 5.4-based
    > tree with SMP, DEVICE_POLLING and fxp:
    > http://lists.freebsd.org/pipermail/freebsd-stable/2005-May/015376.html
    > Contrary to my earlier assertion, em does not have a problem.
    >
    > We do have a fair amount of local diffs, so I've now confirmed this is easily
    > reproduced on unmodified -CURRENT as of 05/28.
    >
    > My config file has
    > options SMP
    > options DEVICE_POLLING
    > device fxp
    > (full config file at http://www.maste.org/~ed/sv/STOCK.1 )
    >
    > lock order reversal
    > 1st 0xa0783860 Giant (Giant) @ /d2/emaste/cvs_head/src/sys/kern/kern_poll.c:332
    > 2nd 0xa23e22a0 fxp0 (network driver) @ /d2/emaste/cvs_head/src/sys/dev/fxp/if_fxp.c:1473
    > KDB: stack backtrace:
    > kdb_backtrace(0,ffffffff,a07a6168,a07a4750,a0759160) at 0xa0585789 = kdb_backtrace+0x29
    > witness_checkorder(a23e22a0,9,a070a173,5c1) at 0xa058f74c = witness_checkorder+0x55c
    > _mtx_lock_flags(a23e22a0,0,a070a173,5c1) at 0xa05652f8 = _mtx_lock_flags+0x60
    > fxp_poll(a23e2000,1,5) at 0xa04fa001 = fxp_poll+0x29
    > netisr_poll(0) at 0xa0567070 = netisr_poll+0x188
    > swi_net(0) at 0xa05d9041 = swi_net+0x81
    > ithread_loop(a2309000,c5d8fd38,a2309000,a055aba8,0) at 0xa055acc8 = ithread_loop+0x120
    > fork_exit(a055aba8,a2309000,c5d8fd38) at 0xa055a0f0 = fork_exit+0xa0
    > fork_trampoline() at 0xa06ad31c = fork_trampoline+0x8
    >
    > The ether_poll_deregister in fxp_stop() looks to be the culprit.
    >
    This LOR is well-known and will go away as soon as we commit our WIP
    changes for polling(4). I have no firm plans when it happens though.

    Cheers, 

    -- 
Ruslan Ermilov
ru@FreeBSD.org
FreeBSD committer

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