Re: kernel freeze (not even an OOPS) on remount-ro+umount when using quotas

[Michael Tokarev <mjt@tls.msk.ru>]

Michael Tokarev wrote:
> Steven Rostedt wrote:
> 
>> On Fri, 7 Oct 2005, Michael Tokarev wrote:
>>
>>
>>> This is something that has biten me quite successefully
>>> in last few days... ;)
>>>
>>> To make a long story short:
>>>
>>> # mke2fs -j /dev/hda6
>>> # mount -o usrquota /dev/hda6 /mnt
>>> # cp -a /home /mnt                # to make some files to work with
>>> # quotacheck -uc /mnt
>>> # quotaon /mnt
> 
> Looks like it's more reproduceable when there's some writing
> going on at this point - after enabling the quotas and before
> remointing it read-only.  Maybe there's some unwritten quota
> data left in memory at the remount, or something like that...

Yes it is:
   # quotaon /mnt; touch /mnt/file; mount -o remount,ro /mnt; umount /mnt
and voila, instant freeze.

>>> # mount -o remount,ro             # this is the important step!
>>> # ls -l /mnt /mnt/home            # to do "something" (also important)
>>> # umount /mnt
>>>
>>> At this time (attempting to umount the read-only filesystem with quotas
>>> enabled), the machine freezes without any messages on the console.  No
>>> OOPS, no response, no nothing - until a hard reboot (powercycle).
[]
> And hee-hoo, sysrq works!  Strange I haven't noticied it before - I think
> I tried it on the laptop, maybe I pressed some wrong button...
> 
> Now, as I don't have another PC here @home, only this machine and an ADSL
> router (small mips-based device wich is also running linux), and I will
> not have access to another machine(s) till monday... I'll try netconsole
> to the router.  Damn, why ShiftPgUp does not work as it worked in 2.4?? :(

Nope, my ADSL router is too slow to accept printks from netconsole, or
my PC is too fast (which isn't at all fast - it's a 900MHz VIA C3 system) --
sysrq+t output captured by the router (simple recvfrom()+write(tmpfs) loop)
is *very* incomplete, only shows about 50 lines for all the tasks running...
The device is 150MHz mips-el, texas instruments ar7 (avalanche/sangam) board.

Any suggestions on how to improve the logging? :)

But.  With the above sequence of commands, looks like the problem is pretty
easy to reproduce...

/mjt