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SubjectRe: How to understand an oops?
On Tue, 23 Sep 2003 19:31:10 +0200 "Sebastian Piecha" <spi@gmxpro.de> wrote:

| >...
| > | Does the code section mean that the kernel panic occurred during
| > | execution of this code?
| >
| > Yes.
| > Are there a few informative lines missing before the Oops: line below?

I was expecting more like (cut from source code):

("Unable to handle kernel NULL pointer dereference");
or
("Unable to handle kernel paging request");
and
(" at virtual address %08lx\n",address);
(" printing eip:\n");
("%08lx\n", regs->eip);
("*pde = %08lx\n", page);
("*pte = %08lx\n", page);

| Only the following lines:
| ksymoops 2.4.8 on i686 2.4.23pre1-usbtest. Options used
| -V (specified)
| -k ksyms (specified)
| -l modules (specified)
| -o /lib/modules/2.4.23pre1-usbtest/ (default)
| -m System.map (specified)
|
| > | How likely is it that a bug in net/core/skbuff.c is causing the
| > | kernel panic?
| >
| > Dunno. It's trying to access memory at (%ebx) == 00200000.
| > That could be a single-bit error in memory which was supposed to be
| > 0, which would have terminated the while loop in skb_drop_fraglist().
| >
| > The common suggestion based on this would be to run memtest86
| > (or memtst86 ?) overnight to check for memory errors.
| >
|
| I already run memtest for about 25 hours without any error.
| If it's not a memory error how can I find out what caused the error?
| Debugger?
|
| > | How can I find other code/modules from which skb_drop_fraglist is
| > | called and used?
| >
| > Use grep (or cscope, but that would be overkill in this case).
| > I found it only in net/core/skbuff.c.
| >

In the meantime, you haven't tried the other mailing lists that
I suggested....

| What I found out in the meantime:
| skb_drop_fraglist is part of sk_buff and sk_buff is used by network
| drivers and it seems also IDE drivers. There's a documentation how to
| use sk_buff (Network Buffers and Memory Management, Alan Cox,
| http://www.linuxjournal.com/article.php?sid=1312).
|
| > | What is the best way interpreting such an oops?
| > |
| > | ################## oops #####################
| > | Oops: 0000
| > | CPU: 0
| > | EIP: 0010:[<c0219cd7>] Not tainted
| > | Using defaults from ksymoops -t elf32-i386 -a i386
| > | EFLAGS: 00010206
| > | eax: c40866a0 ebx: 00200000 ecx: c40866a0 edx: 00200000
| > | esi: cec57360 edi: fffffff9 ebp: 00000046 esp: c0303f2c
| > | ds: 0018 es: 0018 ss: 0018
| > | Process swapper (pid: 0, stackpage=c0303000)
| > | Stack: cec57360 c0219d6e cec57360 cec57360 cec57360 c0219dab cec57360
| > | cec57360
| > | c0219efc cec57360 cf49cb20 c021e173 cec57360 00000003 c032c568
| > | c0120629
| > | c032c568 00000006 0000000e c0303f98 d3e02e40 c010a091 c0106f40
| > | c0302000
| > | Call Trace: [<c0219d6e>] [<c0219dab>] [<c0219efc>] [<c021e173>]
| > | [<c0120629>]
| > | [<c010a091>] [<c0106f40>] [<c010c4e8>] [<c0106f40>] [<c0106f64>]
| > | [<c0106fd2>]
| > | [<c0105000>]
| > | Code: 8b 1b 8b 42 74 48 74 0a ff 4a 74 0f 94 c0 84 c0 74 07 52 e8
| > |
| > |
| > | >>EIP; c0219cd7 <skb_drop_fraglist+17/40> <=====
| > ^^^^^^^^^^^^^^^^^^^^^^^
| > This is the faulting code location.
| >
| > | >>eax; c40866a0 <_end+3cf81fc/14e64bbc>
| > | >>ecx; c40866a0 <_end+3cf81fc/14e64bbc>
| > | >>esi; cec57360 <_end+e8c8ebc/14e64bbc>
| > | >>esp; c0303f2c <init_task_union+1f2c/2000>
| >
| > This is the call stack. skb_drop_fraglist() was called from here:
| > vvvvvvvvvvvvvvvvvvvvvv
| > | Trace; c0219d6e <skb_release_data+4e/80>
|
| What does +4e/80 mean in the line above?

That's the return address from skb_drop_fraglist() back to
skb_release_data(): 0x4e bytes into the function, which is
a total of 0x80 bytes long.

--
~Randy
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