background fsck, softupdates & inconsistent state on disk

[Marc Olzheim]

On Thu, Jul 21, 2005 at 11:45:33AM +0200, Marc Olzheim wrote:
> Having enough opportunities to do crash recovery with kern/83375 open
> and some of my services not yet moved back to FreeBSD 4, I noticed that
> often it crashes just after (or perhaps during) mirroring of a directory
> tree. The mirroring involves creating a directory with in it 80
> subdirectories in it.
> 
> Now when the machine panics on a 'screen' again, background fsck fails
> to properly check the filesystem and reports so in /var/log/messages.
> What I see on that partition is the main directory that should have
> contained the 80 subdirs, but now it has a link count of 0 and so
> doesn't even contain a . or .. , let alone the 80 directories that
> should have been there.
> 
> The only thing a manual fsck can do after that is unlink the
> unreferenced inodes and clear up the mess...

Ok, this time it's worse; Trying to startup single user, gives:

WARNING: / was not properly dismounted
start_init: trying /sbin/init
WARNING: R/W mount of / denied.  Filesystem is not clean - run fsck
WARNING: R/W mount of / denied.  Filesystem is not clean - run fsck
WARNING: R/W mount of / denied.  Filesystem is not clean - run fsck
...

And it won't snap out of it...

Luckily we start a 'remote control daemon' before fsck is started, so I
managed to run 'fsck /' manually:

rcntlc> shell sh -i
Press CTRL-A to escape from this mode
sh: can't access tty; job control turned off
# fsck /
** /dev/da0s1a
** Last Mounted on /
** Root file system
** Phase 1 - Check Blocks and Sizes
** Phase 2 - Check Pathnames
** Phase 3 - Check Connectivity
** Phase 4 - Check Reference Counts
** Phase 5 - Check Cyl groups
2174 files, 29734 used, 97105 free (225 frags, 12110 blocks, 0.2% fragmentation)

***** FILE SYSTEM MARKED CLEAN *****
#

So I'm not sure what the problem was...

> Shouldn't this be impossible without power loss ? Or is it inherent to
> SMP that the machine can crash on a process on CPU #0 while CPU #1 is
> updating disk structures ?

Marc
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