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    SubjectRe: UBIFS: Oops while rebooting 2.6.34-rc6
    On Fri, May 07, 2010 at 06:23:46PM +0300, Artem Bityutskiy wrote:
    > On Fri, 2010-05-07 at 15:16 +0200, Daniel Mack wrote:
    > > Hi,
    > >
    > > We've had a kernel Oops today when rebooting an ARM PXA based machine
    > > while file I/O via SSH was outstanding.
    > >
    > > Daniel
    > >
    > > # reboot
    > > # [ 671.190085] UBIFS: un-mount UBI device 0, volume 1
    > > The system is going down NOW!
    > > Sent SIGTERM to all processes
    > > [ 672.083833] Unable to handle kernel NULL pointer dereference at virtual address 000000ac
    > > [ 672.094587] pgd = c0004000
    > > [ 672.097301] [000000ac] *pgd=00000000
    > > [ 672.100850] Internal error: Oops: 817 [#1]
    > > [ 672.104919] last sysfs file: /sys/devices/platform/spi_gpio.0/spi0.2/value
    >
    > It's Firday, and I want to go home, so here is another quick idea for
    > you where to dig.
    >
    > When the system reboots it re-mounts the FS to RO mode, usually. And
    > there is some emergency remount business (see do_emergency_remount()),
    > which will re-mount the FS even if there are files opened for writing.
    >
    > So, if there is a UBIFS or VFS bug, and somehow one process is in
    > make_reservation() and is about to write something, and another process
    > managed to re-mount the FS to R/O mode, then we may ooops, because UBIFS
    > frees these 'wbuf' objects when it is mounted to R/O (see
    > ubifs_remount_ro()).
    >
    > So, inject printks to ubifs_remount_ro() to check this theory.
    >
    > Have a nice weekend and bughunting!

    Thanks for your feedback - I'll give that a try next week.

    Have a good weekend :)

    Daniel


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