lkml.org 
[lkml]   [2008]   [Nov]   [27]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: 2.6.28-rc6-git1 -- BUG: unable to handle kernel paging request at ffff8800be8b0019
Hi,

(I'm jumping in as Andrew forwarded the bug to us thinking it's SLUB related.)

On Thu, Nov 27, 2008 at 1:26 AM, Rafael J. Wysocki <rjw@sisk.pl> wrote:
>> [ 3866.841128] RIP [<ffffffff80262f07>] kallsyms_lookup+0x20/0x120
>> [ 3866.841134] RSP <ffff880073d63da8>
>> [ 3866.841136] CR2: ffff8800be8b0019
>> [ 3866.841140] ---[ end trace ebccc2f1a2509fb0 ]---
>
> Did that happen after a resume from suspend to RAM, by chance?

Could be. I looked at the oops and I'm pretty sure SLUB is not at
fault here. Decoding the oopsing code:

[ 3866.841062] Code: df e8 39 d2 ff ff 5b 41 5c c9 c3 55 48 89 e5 41 57 49 89
cf 41 56 49 89 f6 41 55 49 89 d5 41 54 4d 89 c4 53 48 89 fb 48 83 ec
08 <41> c6
40 7f 00 41 c6 00 00 48 81 ff 00 90 20 80 72 09 48 81 ff

results in:

0000000000000000 <.text>:
0: 41 c6 40 7f 00 movb $0x0,0x7f(%r8) <<<<----
5: 41 c6 00 00 movb $0x0,(%r8)
9: 48 81 ff 00 90 20 80 cmp $0xffffffff80209000,%rdi
10: 72 09 jb 0x1b
12: 48 rex.W
13: 81 .byte 0x81
14: ff .byte 0xff
which looks like this:

000000000000023e <kallsyms_lookup>:
*/
const char *kallsyms_lookup(unsigned long addr,
unsigned long *symbolsize,
unsigned long *offset,
char **modname, char *namebuf)
{
23e: 41 56 push %r14
240: 49 89 f6 mov %rsi,%r14
243: 41 55 push %r13
245: 49 89 d5 mov %rdx,%r13
248: 41 54 push %r12
24a: 49 89 cc mov %rcx,%r12
24d: 55 push %rbp
24e: 48 89 fd mov %rdi,%rbp
251: 53 push %rbx
namebuf[KSYM_NAME_LEN - 1] = 0;
252: 41 c6 40 7f 00 movb $0x0,0x7f(%r8) <<<<----
*/
That is, we're oopsing because someone is passing a bogus 'namebuf' to
kallsyms_lookup(). This is further confirmed by looking at the value of R8:

[ 3866.840962] RBP: ffff880073d63dd8 R08: ffff8800be8aff9a R09:
0000000000000000
and adding 0x7f to it:

0xffff8800be8aff9a + 0x7f = 0xffff8800be8b0019
which equals to the faulting address:

[ 3866.840809] BUG: unable to handle kernel paging request at ffff8800be8b0019
Furthermore, the value of KSYM_NAME_LEN is 128 so the offset matches as well
after subtracting one from it (0x7f).

Looking at the call trace:

[ 3866.841017] Call Trace:
[ 3866.841020] [<ffffffff8026302f>] sprint_symbol+0x28/0xaa
[ 3866.841025] [<ffffffff8029e972>] list_locations+0x170/0x2ef
[ 3866.841031] [<ffffffff8029eb34>] alloc_calls_show+0x1c/0x24
[ 3866.841036] [<ffffffff8029cbbc>] slab_attr_show+0x23/0x27
[ 3866.841041] [<ffffffff802efdff>] sysfs_read_file+0xba/0x13c
[ 3866.841046] [<ffffffff802a4795>] vfs_read+0xa4/0xde
[ 3866.841052] [<ffffffff802a4893>] sys_read+0x47/0x6e
[ 3866.841056] [<ffffffff8020b6fb>] system_call_fastpath+0x16/0x1b
we can see that kallsyms_lookup() is being called by sprint_symbol() which is,
in turn, called by the SLUB code. However, SLUB never touches 'namebuf',
instead it's being allocated on the stack by sprint_symbol():

/* Look up a kernel symbol and return it in a text buffer. */
int sprint_symbol(char *buffer, unsigned long address)
{
char *modname;
const char *name;
unsigned long offset, size;
char namebuf[KSYM_NAME_LEN];
name = kallsyms_lookup(address, &size, &offset, &modname, namebuf);

Hmm?

Pekka


\
 
 \ /
  Last update: 2008-11-27 14:41    [from the cache]
©2003-2011 Jasper Spaans