Re: [uml-devel] "Kernel panic: Segfault with no mm"

[Oleg Drokin <green@linuxhacker.ru>]

Hello!

Lars Marowsky-Bree <lmb@suse.de> wrote:

LMB> with the UML kernel on 2.4.21 I am seeing the above. I can trigger it by
LMB> a NULL pointer dereference in the kernel (ie, my buggy code / module
LMB> ;-).

Well. This is expected.

LMB> Instead of a regular panic, I get the above. It appears something is
LMB> going astray with the mm handling.
LMB> #0  panic (fmt=0xa01b8ad2 "Segfault with no mm") at panic.c:59

So it said you had segfault in kernel.

LMB> #1  0xa00af3b4 in segv (address=1074944004, ip=2706132208, is_write=0, 
LMB>     is_user=0, sc=0xa1468280) at trap_kern.c:119
LMB> #2  0xa00af866 in segv_handler (sig=11, regs=0xa1468280) at trap_user.c:69
LMB> #3  0xa00b351c in sig_handler_common_tt (sig=11, sc_ptr=0x58) at trap_user.c:37
LMB> #4  0xa00af990 in sig_handler (sig=1, sc=
LMB>       {gs = 0, __gsh = 0, fs = 0, __fsh = 0, es = 43, __esh = 0, ds = 43, __dsh = 0, edi = 2694189056, esi = 2694189056, ebp = 2705767004, esp = 2705766988, ebx = 4294967295, edx = 0, ecx = 2705766824, eax = 2706243584, trapno = 13, err = 0, eip = 2706132208, cs = 35, __csh = 0, eflags = 66118, esp_at_signal = 2705766988, ss = 43, __ssh = 0, fpstate = 0x0, oldmask = 436281344, cr2 = 1074944004})
LMB>     at trap_user.c:104
LMB> #5  <signal handler called>

This is signal kernel and one step up is your buggy code.
You just need to go up to that point to see what's wrong.

LMB> I wonder whether anyone has seen that before or whether it is something
LMB> peculiar to my setup. (Which also includes the aa patches for the VM)

I always see this stuff when kernel does such bad things and I sort of
understand that it should be this way.


Bye,
    Oleg


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