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

[Michael Tokarev]

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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