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Date: Sun, 4 Jul 2004 11:11:21 -0400 (EDT)
From: Robert Watson <rwatson@freebsd.org>
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To: Niklas Saers <niklasmls@saers.com>
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cc: freebsd-current@freebsd.org
Subject: Re: Filesystem lock in jailed environment
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On Sun, 4 Jul 2004, Niklas Saers wrote:

> I'm not an experienced kernel-debugger, and hitting Ctrl-Alt-Esc only
> gives me a trace of the keyboard. If this is a good route to take, hints
> to how to go about are most welcome. 

Sounds like a file system vnode lock deadlock.  Try using the "show
lockedvnodes" command to identify locked vnodes and processes holding
them; then use the "trace <pid>" command to trace the processes in
question to see where they blocked while holding vnode locks.  It may be
useful to build your kernel with "options DEBUG_LOCKS", which will provide
additional information about vnode locking (at a performance hit) -- in
particular, it will have each lock trace where the lock was last acquired.

If you're running with WITNESS, you can use the WITNESS debugging features
to identify other potential deadlocks.  However, it sounds like this is a
vnode deadlock, and vnodes use "lockmgr" for their higher level locking,
and lockmgr isn't currently able to use WITNESS.

Robert N M Watson             FreeBSD Core Team, TrustedBSD Projects
robert@fledge.watson.org      Principal Research Scientist, McAfee Research