Recurring problem: processes block accessing UFS file system

[Don Lewis]

On 26 Nov, Tor Egge wrote:
> 
>> Thanks Kris, these are exactly the clues I needed.  Since the deadlock 
>> during a snapshot is fairly easy to reproduce, I did so and collected this 
>> information below.  "alltrace" didn't work as I expected (didn't produce a 
>> trace), so I traced each pid associated with a locked vnode separately.
> 
> The vnode syncing loop in ffs_sync() has some problems:

There is also a MNT_VNODE_FOREACH() loop in ffs_snapshot().