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Date:      Mon, 29 Jun 2009 16:21:16 +0300
From:      Kostik Belousov <kostikbel@gmail.com>
To:        pluknet <pluknet@gmail.com>
Cc:        Attilio Rao <attilio@freebsd.org>, freebsd-stable <freebsd-stable@freebsd.org>
Subject:   Re: [nfs] process locks in "bo_wwait" on 6.4
Message-ID:  <20090629132116.GZ2884@deviant.kiev.zoral.com.ua>
In-Reply-To: <a31046fc0906290618r31e5bfb0h9e267fadef53408a@mail.gmail.com>
References:  <a31046fc0906260944h68eed26bs256dcad1f29871ff@mail.gmail.com> <a31046fc0906260951i66c239e1yfac9048d69784209@mail.gmail.com> <a31046fc0906290329p3e9cff1dwa89c8bb88736fed7@mail.gmail.com> <3bbf2fe10906290458v3d57441ar44c4ed8f36c957f@mail.gmail.com> <a31046fc0906290555ib9abf4fy90502eb01e2ef8d3@mail.gmail.com> <3bbf2fe10906290611j683a0ddawbd524e406e832d54@mail.gmail.com> <a31046fc0906290618r31e5bfb0h9e267fadef53408a@mail.gmail.com>

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On Mon, Jun 29, 2009 at 05:18:03PM +0400, pluknet wrote:
> 2009/6/29 Attilio Rao <attilio@freebsd.org>:
> > 2009/6/29 pluknet <pluknet@gmail.com>:
> >> 2009/6/29 Attilio Rao <attilio@freebsd.org>:
> >>> 2009/6/29 pluknet <pluknet@gmail.com>:
> >>>> 2009/6/26 pluknet <pluknet@gmail.com>:
> >>>>> 2009/6/26 pluknet <pluknet@gmail.com>:
> >>>>>> Hello.
> >>>>>>
> >>>>>> While building a module on nfs mounted /usr/src
> >>>>>> I got an unkillable process waiting forever in bo_wwait.
> >>>>>
> >>>>> Small note: iface on NFS server has mtu changed from 1500 to 1450.
> >>>>> Can this be a source of the problem?
> >>>>
> >>>> This is 100% reproducible. Lock in the same place. Any hints?
> >>>
> >>> Can you also show the value of ps?
> >>> A precise map of what processes are doing would give an help.
> >>> Also would be useful to printout traces for other threads and not only
> >>> the stucked one.
> >>>
> >>
> >> >From another run:
> >
> > I'm unable to see who would be locking the buffer object in question.
> > Do you have INVARIANT_SUPPORT/INVARIANTS on?
>=20
> Yes, I do both.
>=20
> > What revision of /usr/src/sys/kern/vfs_bio.c are you running with?
> >
>=20
> As of 6.4-R: CVS rev 1.491.2.12.4.1 / SVN rev 183531.

It seems that your changes of MTU cause nfs requests to never reach
network. bo_wwait is the state where thread waits for all outstanding
i/o on bufobj to drain.

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