Date: Sun, 27 Jun 1999 01:15:43 -0700 (PDT) From: Matthew Dillon <dillon@apollo.backplane.com> To: Peter Wemm <peter@netplex.com.au> Cc: current@FreeBSD.ORG, mckusick@mckusick.com Subject: Re: BUF_LOCK() related panic.. Message-ID: <199906270815.BAA10773@apollo.backplane.com> References: <19990627075755.901EA82@overcee.netplex.com.au>
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Ah, yes, some of us were just discussing this in a small mailing list.
Hopefully Kirk will pick up on it soon. Ah well.. someone else gets to be
the brunt of it for a change :-). Kirk doesn't have an SMP box so he
didn't see the bug.
I have tentitively tracked the problem down to the apparent inability of
lockmgr() locks to function from interrupts, even when used in a
non-blocking manner, due to the simplelock's it uses internally. The
new buffer cache code Kirk committed switched from B_BUSY (manually
implemented locks) to lockmgr() locks. I think what is going on is
that mainline code is getting a simplelock and then an interrupt is
coming along and also trying to get the same lock, but I can't be sure
because my DDB backtraces are somewhat munged.
I was hoping someone would come up with a quick hack to solve the
problem, but baring that I do have a big nasty patch on my site
http://www.backplane.com/FreeBSD4/ which replaces the use of lockmgr()
locks in the buffer cache code with the new SMP qlock's I began working
on yesterday - but I wasn't intending on submitting it for commit for a
while -- even the SMP guys haven't seen it yet! This patch is currently
only suitable for compiling a new i386 -CURRENT kernel, it will break
buildworld and it will also break alpha builds. And it has not been
well tested yet... it is running a whole lot of brand new untested code
and I'm amazed that it works as well as it does :-)
If you do not want to get that involved, you can turn off SMP on the
system and it should boot ok. Also be sure to completely recompile
your modules (/usr/src/sys/modules), and when cvs updating be sure
to update /usr/src/contrib/sys as well as /usr/src/sys/ if you are
using softupdates. The size of struct buf has changed radically.
-Matt
Matthew Dillon
<dillon@backplane.com>
:I pressed reset, even break-to-debugger didn't work..
:
:To provoke it, do this once or twice:
:
:root:[3:21pm]/etc-104# passwd root
:Changing local password for root.
:New password:
:Retype new password:
:passwd: updating the database...
:Read from remote host beast: Operation timed out
:Connection to beast closed.
:
:I'll look into this more shortly...
:
:Cheers,
:-Peter
:--
:Peter Wemm - peter@FreeBSD.org; peter@yahoo-inc.com; peter@netplex.com.au
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