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Date:      Sat, 5 Oct 2002 13:30:36 -0400 (EDT)
From:      Robert Watson <rwatson@freebsd.org>
To:        "Steven G. Kargl" <kargl@troutmask.apl.washington.edu>
Cc:        "Brian F. Feldman" <green@freebsd.org>, freebsd-current@freebsd.org, kirk@freebsd.org
Subject:   Re: panic from _mutex_assert in kern_lock.c
Message-ID:  <Pine.NEB.3.96L.1021005132846.64999n-100000@fledge.watson.org>
In-Reply-To: <200210051723.g95HNxKv014164@troutmask.apl.washington.edu>

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On Sat, 5 Oct 2002, Steven G. Kargl wrote:

> I came to the same conclusion after I sent the original email. 
> 
> What I don't understand is how I ended up in ffs_snapshot(), because I
> don't have a snapshot of /var.  I tried snapshots when Kirk first
> introduced the feature, but I removed all of the snapshots a long time
> ago.  Is there a flag in the superblock that I need to clear? 
> 
> One other point, the machine was doing a background fsck on /var.  Does
> a background fsck go through ffs_snapshot()? 

Yes -- the background file system checker creates a snapshot of the file
system in the un-checked state, then performs the check against the
snapshot.  It trickles the changes generated against the snapshot into the
live file system.  Because of the conservative nature of failures with
soft updates, the only theoretical inconsistencies relate either to marked
as non-free yet unreferenced resources, and referenece counts that are
high.  The snapshot allows fsck a consistent view of the file system "as
it was" so that it doesn't get confused by the live file system. 

Robert N M Watson             FreeBSD Core Team, TrustedBSD Projects
robert@fledge.watson.org      Network Associates Laboratories



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