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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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