fsck_ufs locked in snaplk

[Dmitry Morozovsky]

On Mon, 24 Apr 2006, Dmitry Morozovsky wrote:

DM> kKK> > one of my servers had to be rebooted uncleanly and then I have backgrounded 
DM> KK> > fsck locked for more than an our in snaplk:
DM> KK> > 
DM> KK> > 742 root         1  -4    4  1320K   688K snaplk   0:02  0.00% fsck_ufs
DM> KK> > 
DM> KK> > File system in question is 200G gmirror on SATA. Usually making a snapshot 
DM> KK> > (e.g., for making dumps) consumes 3-4 minutes for that fs, so it seems to me 
DM> KK> > that filesystem is in a deadlock.
DM> KK> 
DM> KK> Is the process performing I/O?  Background fsck deliberately runs at a
DM> KK> slow rate so it does not destroy I/O performance on the rest of the
DM> KK> system.
DM> 
DM> Nope. For that case, 50+ smbds had been locked in 'ufs' state, so I've been 
DM> urged to revive the machine and reboot, turning off bgfsck.
DM> 
DM> This night, dump -L locks in the same position on the same filesystem:
DM> 
DM> 0  2887  2886   0  -4  0  1260   692 snaplk D     ??    0:01.28 
DM> /sbin/mksnap_ffs root    0.0  0.1  5:19AM
DM> 
DM> it has been started at 5:19am, and now is 9:20 - no disk activity
DM> 
DM> 
DM> For the reference: it's fresh RELENG_6_1/i386.

Just rechecked it: did mksnap_ffs on an otherwise idle file system:

marck at office:/> mksnap_ffs /st /st/.snap/test_snapshot
load: 0.02  cmd: mksnap_ffs 4012 [biord] 0.00u 0.04s 0% 696k
load: 0.04  cmd: mksnap_ffs 4012 [biord] 0.00u 0.44s 0% 696k
load: 0.21  cmd: mksnap_ffs 4012 [snaprdb] 0.00u 1.17s 0% 696k
load: 0.20  cmd: mksnap_ffs 4012 [snaprdb] 0.00u 1.23s 0% 696k
load: 0.13  cmd: mksnap_ffs 4012 [snaplk] 0.00u 1.30s 0% 696k
load: 0.08  cmd: mksnap_ffs 4012 [snaplk] 0.00u 1.30s 0% 696k
load: 0.01  cmd: mksnap_ffs 4012 [snaplk] 0.00u 1.30s 0% 696k

(I hit ^T several times)

biord phase consumes about 1.5-2 mins,
snaprdb phase - about 30-40 secs, and then process died. Most disk requests
succeeds; however, accessing /st/.snap locks process in ufs state forever.

What bothers me most is that it is the only machine reproducibly hangs in 
snapshots, and it did not hang before RELENG_5 -> RELENG_6 upgrade. Other 
RELENG_6 machines do snapshot backups flawlessly (knock-on-wood!)

Sincerely,
D.Marck                                     [DM5020, MCK-RIPE, DM3-RIPN]
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*** Dmitry Morozovsky --- D.Marck --- Wild Woozle --- marck at rinet.ru ***
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