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SubjectRe: 2.6.32 regression, hard lock
At Mon, 7 Dec 2009 16:48:26 -0800,
Andrew Morton wrote:
>
> On Tue, 8 Dec 2009 01:23:53 +0100
> Richard Zidlicky <rz@linux-m68k.org> wrote:
>
> >
> > > > first visible symptom is that ppp over UMTS connection "stops working", connection
> > > > did not die. Trying to restart the connection fails and the related processes hang.
> > > >
> > > > After that one after another everything stops working, "telinit 6" does not do its
> > > > job and SysRQ sync-umount-reboot is logged in messages but has no visible effect.
> > > >
> > > > Attaching messages and .config.
> > > >
> > >
> > > I uploaded your dmesg output to
> > > http://userweb.kernel.org/~akpm/stuff/messages.txt
> >
> > >
> > > I'm looking at those traces and am not able to develop a theory to
> > > explain it :(
> >
> > thanks for looking at it.
> >
> > I did revert to 2.31.5 and to my big surprise found a similar thing happened
> > so it is not a regression, at least not from 2.6.31.
>
> This trace is different. It's a lock ranking warning and is surely
> unrelated to the IRQs-off lockup which you earlier experienced.
>
(snip)
> And fortunately I know who to cc on this one ;)

Oh, it's a pity to me that you know that ;)

It's a known issue for several kernel releases. (There are a few
subsystems that have the similar lockdep pattern involving with
mm->mmap_sem, too.)

But, as Andrew pointed, this should be irrelevant with the IRQ
lockup. At most it could be a dead-locking of PA and other
sound-related processes, but I've never heard the real issue.


thanks,

Takashi


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