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	Mon, 27 Jul 1998 14:44:19 +1000
Date: Mon, 27 Jul 1998 14:44:19 +1000
From: Bruce Evans <bde@zeta.org.au>
Message-Id: <199807270444.OAA10989@godzilla.zeta.org.au>
To: cradek@in221.inetnebr.com, freebsd-current@FreeBSD.ORG
Subject: Re: ext2fs and sync panic, still
Sender: owner-freebsd-current@FreeBSD.ORG
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>I have run into the problem where mounting an ext2fs r/w panics as 
>soon as sync is called.  r/o has no problems.  This is from current 
>as of a couple days ago.
>
>This panic is due to a null pointer dereference in ext2_sync
>(ext2_vfsops.c:858) caused by a vnode with a NULL v_data.  There is a 

This is because ext2fs hasn't been updated to work with the softupdates
syncer daemon.

>comment in ext2_vget warning of a blocking MALLOC() that might cause 
>this, but I don't understand the comment.  Can someone explain this 
>to me?  My first thought was that this was an SMP locking problem, 
>but a uniprocessor kernel gives the same behavior.

This is unrelated.  There is a race that only occurs every billionth
(or thereabouts) call to getnewvnode().

>Unfortunately I can't get a memory dump from this machine because I am
>running it diskless.  (correct me if this is wrong!)  I want to
>convert it (gently) from Linux and to do this I need to run it diskless
>and mount my ext2 filesystems.

I wouldn't trust ext2fs except for read-only mounts, especially for this.

It is possible to share the swap partition and then easy to dump to it.

Bruce

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