[Bugme-janitors] [Bug 14638] New: device mapper unaccounted null pointer

bugzilla-daemon at bugzilla.kernel.org bugzilla-daemon at bugzilla.kernel.org
Wed Nov 18 16:38:00 PST 2009


http://bugzilla.kernel.org/show_bug.cgi?id=14638

           Summary: device mapper unaccounted null pointer
           Product: IO/Storage
           Version: 2.5
    Kernel Version: 2.6.32-rc7
          Platform: All
        OS/Version: Linux
              Tree: Mainline
            Status: NEW
          Severity: high
          Priority: P1
         Component: Other
        AssignedTo: io_other at kernel-bugs.osdl.org
        ReportedBy: bugzilla at synx.us.to
        Regression: No


I've been using cryptsetup to access an external hard drive of mine via an
encrypted mapping, pointing postgresql towards it for (relatively) steady disk
access. I upgraded to Mainline (2.6.32-rc7) and found that within a day or so
the device mapper would somehow mysteriously "lose" its mapping entirely. The
mount point remains mounted, but cannot even be statted, as "ls: cannot access
/media/extern". When I umount /media/extern, it works without error, but
"cryptsetup remove extern" fails permanenty, necessitating a full reboot.

cryptsetup I'm pretty sure is a front-end for the device mapper, using the
dm-crypt module. Not sure if that would specifically be a problem. What happens
is I type "cryptsetup status extern" and it reports to me the following:

/dev/mapper/extern is active:
  cipher:  aes-cbc-essiv:sha256
  keysize: 256 bits
  device:  (null)
  offset:  0 sectors
  size:    310472190 sectors
  mode:    read/write

where it says "device: (null)" it should obviously say "device: /dev/sdb1". It
initially did say that, and worked perfectly normally. But some unknown trigger
(while I was away from the computer to boot) causes the pointer to the device
to be overwritten with a null pointer.

I don't know much about the device mapper, or how to get more detailed
statistics, or any possible solutions to the problem. But I didn't see it
posted as a bug, so thought I'd point it out so wiser folks than me can know
what to look out for. I'm going back to 2.6.31.6 to see if the problem is there
too, or if it was a recent addition.

I'm on an amd64 system, with an external USB hard drive enclosure that's never
given me any problems before. It's still powered up and there's no error
regarding it in dmesg, and fdisk -l /dev/sdb gives me perfectly normal
readings, so I don't think it's a hard disk failure, but instead a failure of
something in the mount-point/device mapper/device chain.

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