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    SubjectRe: 2.5.69+bk: oops in apmd after waking up from suspend mode
    On Wed, 14 May 2003 11:48:13 +0200, Alex Riesen wrote:
    >I have an old Compaq Armada 1592DT. The thing goes automagically into
    >suspend mode after being forgotten for a while. And there is this button
    >to wake it up (the blue one, above the keyboard).
    >
    >Last time i tried to wake it up it produced the attached oops.
    >"Unknown key"s are probable the blue button.
    >After printing out the oops, the system went back into suspend.
    >
    >-alex
    >
    >Suspending devices
    >Suspending device c03219ac
    >Unable to handle kernel NULL pointer dereference at virtual address 00000090
    > printing eip:
    >c011459f
    >*pde = 00000000
    >Oops: 0000 [#1]
    >CPU: 0
    >EIP: 0060:[<c011459f>] Not tainted
    >EFLAGS: 00010202
    >EIP is at fix_processor_context+0x5f/0x100
    >eax: 0000007c ebx: c5f0e000 ecx: 00000002 edx: 00000000
    >esi: 00000060 edi: 00000000 ebp: c5f0ff5c esp: c5f0ff54
    >ds: 007b es: 007b ss: 0068
    >Process kapmd (pid: 4, threadinfo=c5f0e000 task=c5fbc640)

    After receiving Alex' .config and gcc version (3.2.3), I've been
    able to decipher this. current->mm is NULL in the kapmd task. The call

    load_LDT(&current->mm->context); /* This does lldt */

    in fix_processor_context() computes the address of context as
    (current->mm)+0x7c, which is 0x7c. load_LDT_nolock() dereferences
    0x7c+0x14 (void *segments = pc->ldt) and the oops follows.

    As to _why_ kapmd's current->mm is NULL, I don't know. It isn't
    when I test APM suspend in 2.5.69-bk. A lot of code dereferences
    current->mm without checking, so I guess current->mm==NULL is a bug.

    /Mikael
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