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

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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...

# 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).

This happens on 2.6.11, 2.6.12 and 2.6.13 kernels -- ie, with "current"
kernel release.

I just tried this on 2.6.13.1 and was not able to reproduce your hangup.

I'm able to reproduce it on almost any my machine.  Tried on several
production machines first ;)  And on at least two test machines.
Now I'm at home and my home PC also shows this bug (2.6.13.1 vanilla).

Have you tried turning on the nmi watchdog with "nmi_watchdog=2 lapic"?

nmi_watchdog makes no visible difference.  Lapic is already enabled, at
least on this machine (BTW, the same behaviour happens on SMP and UP
machines, with and without hyperthreading enabled).

If this blocks interrupts while it spins, you might be able to see what's
happening.  Also if interrupts are not blocked, try out sysrq-t and
friends.

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?? :(

/mjt
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