another wapbl and shapshot issue

[Manuel Bouyer <bouyer%antioche.eu.org@localhost>]

Hello,
I ran into another panic "current transaction too big to flush" while using
snapshots on a 500GB filesystem. This occured when I removed the
snapshot file, and what's worse, it happens also when the kernel replays
the log after reboot.
With more instrumentation in vfs_wapbl.c I found this stack trace at the
time the log overflows:
wapbl_add_buf
bdwrite
bwrite
ffs_snapblkfree
fss_blkfree
ffs_wapbl_sync_metadata
wapbl_flush
wapbl_begin
ufs_inactive
VOP_INACTIVE
vrelel
ffs_wapbl_replay_finish
ffs_wapbl_start
ffs_mountfs
ffs_mount
VFS_MOUNT
...

to me it looks like the usual way of cutting the transaction in smaller pieces
won't work because we're already in wapbl_begin().
Also I wonder if it's OK for wapbl_flush() to cause more data to be
added to the log.

Any idea ?

-- 
Manuel Bouyer <bouyer%antioche.eu.org@localhost>
     NetBSD: 26 ans d'experience feront toujours la difference
--