ffs_blkfree: freeing free block -- ps, traces, fsck log

[Robert Watson]

On Fri, 2 May 2003, Robert Watson wrote:

> I updated a pxe box to a recent -current, and applied it to a UFS
> partition I had on disk.  I ran several parallel tars, an rm -Rf on one
> of the tar extract targets, and a dd if=/dev/zero of=tmp on the
> partition, and within a few minutes reproduced the nefarious
> ffs_blkfree() panic. Some debugging information as follows; I included
> stack traces of some of the more interesting threads.  I've also
> included the fsck output below -- the background file system checker was
> not active at the time as it's manually mounted and fscked when used; I
> believe the file system has never actually had the background file
> system checker used on it, certainly not with a recent kernel.  The
> output from fsck -y on the partition is also attached.  As you can see,
> there are some alarming "ALLOCATED FRAG xxx MARKED FREE" messages. 

Actually, not so alarming -- I misinterpretted that as "allocated flag
*was found* marked as free" rather than "hi, I'm fsck, and these frags
that looked allocated in the free list were actually not used, so I marked
them as free".  The truncated inode message is the one that's actually bad
:-). 

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