Re: determining a "valid" vmcore

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Andrew Hecox wrote:
On Thu, 2008-02-07 at 16:04 -0500, Dave Anderson wrote:
Andrew Hecox wrote:
On Thu, 2008-02-07 at 15:38 -0500, Dave Anderson wrote:
Andrew Hecox wrote:
I get the same:
(/boot/System.map-2.6.9-67.0.1.ELhugemem)

02323bd8 d log_buf_len

(/usr/lib/debug/lib/modules/2.6.9-67.0.1.ELhugemem/vmlinux)

$1 = (int *) 0x2323bd8

-Andrew
So, as Takao suggested, can you dump the incoming vaddr and
resultant pfn values in diskdumpmsg.c:read_buffer()?

The vaddr value is: 36846552.

-Andrew

Dave


OK, so the incoming vaddr is 36846552 is which is 0x2323bd8.
To get a pfn, that hugemem kernel virtual address is passed
through vtop() and then divided by 4096:

static int read_buffer(DumpFile *dump, addr_t vaddr, size_t len, void *buf)
{
         addr_t paddr;
         int block_size = get_page_size();
         unsigned long pfn;
         int ret;
         size_t copy_len, offs;
         void *page_data;

         paddr = vtop(dump, vaddr);
         pfn = paddr / block_size;
         offs = paddr % block_size;

When 0x2323bd8 is run through vtop(), it simply strips off the
hugemem unity-map identifier:

addr_t vtop(DumpFile *dump, addr_t vaddr)
{
         if (strstr("hugemem", dump->utsname->release))
                 return vaddr - 0x02000000L;
         else
                 return vaddr - 0xc0000000L;
}

leaving 0x323bd8 -- which gets divided by the page size of 4096, leaving
a pfn of 0x323.

But you see that the pfn was 271139 (0x42323).  If that is expanded
to a physical address it would be 0x42323000.  It looks like it's
using the non-hugemem value in vtop(), i,e, subtracting c0000000 from
the incoming vaddr.  In other words, 0x2323bd8 - 0xc000000 is
equal to 0x42323bd8.  If that is divided by 4096, you get
the funky pfn of 271139 (0x42323).

Print out the dump->utsname->release string in vtop().  It must
not contain "hugemem".


Dave,

I get:

(gdb) print dump->utsname->release
$19 = "2.6.9-67.0.1.ELhugemem", '\0' <repeats 42 times>

but then

(gdb) s
16                      return vaddr - 0xc0000000L;

! oh uh.

man strstr

...
       char *strstr(const char *haystack, const char *needle);
...

It looks like if (strstr("hugemem", dump->utsname->release))
should be:

	if (strstr(dump->utsname->release,"hugemem"))

Bingo -- like the man page says:

  char *strstr(const char *haystack, const char *needle);


I patched, recompiled, tested and it works:

[root@ibm-x3455-1 ~]# diskdumpmsg -f -p /var/crash/vmcore Jan 31 05:43:08 elabhost012 kernel: --- salvaged messages from crash
dump start
Jan 31 05:43:08 elabhost012 kernel:        0218b9c0 0232d363 0232d3e0
0215aff6 df954fac f6db4000 eaa756c0 fffffff7 Jan 31 05:43:08 elabhost012 kernel: f6db4000 df954000 0215b0c0 df954fac 00000000 00000000 00000000 df954fc4 Jan 31 05:43:08 elabhost012 kernel: Call Trace:
Jan 31 05:43:08 elabhost012 kernel:  [<0220c46a>] __handle_sysrq
+0x58/0xc6
Jan 31 05:43:08 elabhost012 kernel:  [<0218b9c0>] write_sysrq_trigger
+0x37/0x3e
Jan 31 05:43:08 elabhost012 kernel:  [<0215aff6>] vfs_write+0xb6/0xe2
Jan 31 05:43:08 elabhost012 kernel:  [<0215b0c0>] sys_write+0x3c/0x62
Jan 31 05:43:08 elabhost012 kernel: Code: 11 02 c7 05 10 fd 44 02 00 00
00 00 c7 05 38 fd 44 02 00 00 00 00 c7 05 2c fd 44 02 6e ad 87 4b 89 15
28 fd 44 02 e9 8b 41 f2 ff <c6> 05 00 00 00 00 00 c3 e9 0a ff f4 ff e9
a2 48 f5 ff 85 d2 89 Jan 31 05:43:08 elabhost012 kernel: --- salvaged messages from crash
dump end

Thanks much for all the help! Should I open a bz against the issue? It
looks like all i386 hugemem kernels would be similarly affected.

Yep -- definitely open a BZ against component "diskdumputils".

Dave


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