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    Subject2.6.13: loop ioctl crashes
    I'm trying out PPDD from https://retiisi.dyndns.org/~sailus/ppdd/
    because I have some old stuff in that format. However, the crash
    seems to occur in code that isn't touched by the PPDD patch. It
    happens while I'm trying to set up the loop device - I haven't got
    as far as actually using it yet.

    If I'm lucky then when I issue the losetup command and successfully
    type in the passphrase then losetup says something of the form
    ioctl: LOOP_SET_STATUS: Bad address
    and the kernel says:

    Debug: sleeping function called from invalid context at arch/i386/lib/usercopy.c:634
    in_atomic():1, irqs_disabled():0
    [<c011f8eb>] __might_sleep+0xab/0xc0
    [<c0211aa3>] copy_from_user+0x23/0x90
    [<d0a9fe80>] loop_set_status_old+0x30/0x70 [loop]

    However, it often seems to panic in a variety of horrible ways while
    trying to print the above message.

    Clearly I have CONFIG_DEBUG_SPINLOCK_SLEEP set (as my config is
    based on Fedora's), and I suppose I could just try unsetting it to
    make the message go away. That wouldn't make the underlying bug go
    away, though. If it makes any difference, loop and all the crypto
    algorithms are compiled as modules.

    I don't understand why it's an invalid context. I also don't understand
    why the traceback stops at loop_set_status_old given that it must have
    been called from lo_ioctl. (But maybe the answer to the latter would
    explain the former.)

    I may try just moving the copy_from_user() out to the beginning of
    lo_ioctl and see what happens. Any other suggestions? In case it's
    not obvious by now, I'm not really a kernel hacker.

    imc
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