Re: kern/48849: root mirror raid fails on shutdown

[Patrick Welche <prlw1%cam.ac.uk@localhost>]

With your patch, I no longer see any forceful unmounts, however the
computer doesn't shut down either. I sprinkled a few printfs in dounmount(),
and see:

Entering dounmount /var (/dev/raid7e)...
VFS_SYNC(/var) = 0
VFS_UNMOUNT(/var) = 0 
called vfs_hooks_unmount(/var)
Successfully exiting dounmount /var (/dev/raid7e)...
unmounting 0xfffffe811e883008 / (/dev/raid7a)...
Entering dounmount / (/dev/raid7a)...
VFS_SYNC(/) = 0
VFS_UNMOUNT(/) = 16 
unmounting 0xfffffe811e883008 / (/dev/raid7a)...
Entering dounmount / (/dev/raid7a)...
VFS_SYNC(/) = 0
VFS_UNMOUNT(/) = 16 
cd0: detached
atapibus0: detached
[other detached snipped]
raid6: detached
raid5: detached
raid5: detached
-- and this is where we hang

Note there is no "exiting dounmount" for raid7a

Breaking into ddb at this point

Stopped in pid 0.5 (system) at  netbsd:breakpoint+0x5:  leave
db{0}> bt
breakpoint() at netbsd:breakpoint+0x5
comintr() at netbsd:comintr+0x529
Xintr_ioapic_edge1() at netbsd:Xintr_ioapic_edge1+0xea
--- interrupt ---
_kernel_lock() at netbsd:_kernel_lock+0x165
intr_biglock_wrapper() at netbsd:intr_biglock_wrapper+0x12
Xintr_ioapic_level3() at netbsd:Xintr_ioapic_level3+0xf2
--- interrupt ---
_kernel_lock() at netbsd:_kernel_lock+0x165
frag6_fasttimo() at netbsd:frag6_fasttimo+0x1a
pffasttimo() at netbsd:pffasttimo+0x31
callout_softclock() at netbsd:callout_softclock+0x1d0
softint_dispatch() at netbsd:softint_dispatch+0xd3
DDB lost frame for netbsd:Xsoftintr+0x4f, trying 0xfffffe80cd845ff0
Xsoftintr() at netbsd:Xsoftintr+0x4f
--- interrupt ---
0: