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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.
>Suspending devices
>Suspending device c03219ac
>Unable to handle kernel NULL pointer dereference at virtual address 00000090
> printing eip:
>*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.

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