8:53 a.m.
----- "Kevin Worth" <kevin.worth(a)hp.com> wrote:
Hi Dave,
Before you responded I noticed that a simple "make modules" didn't
work because my kernel wasn't exporting the symbol. Rather than do
anything risky/complex which might risk mucking up the troubleshooting
process, I just rebuilt the kernel. It built just fine and now I can
load crash and I see "DUMPFILE: /dev/crash" when I load up crash. Let
me try walking through the steps that you had me do previously, this
time using /dev/crash instead of /dev/mem and /dev/kmem
You made one small error (but not totally fatal) in the suggested steps.
See my comments below...
>From my limited understanding of what's going on here, it would
appear that the dump file is missing some data, or else crash is
looking in the wrong place for it.
The crash utility is a slave to what is indicated in the PT_LOAD
segments of the ELF header of the kdump vmcore. In the case of
the physical memory chunk that starts at 4GB physical on your machine,
this is what's in the ELF header (from your original "crash.log" file):
Elf64_Phdr:
p_type: 1 (PT_LOAD)
p_offset: 3144876760 (bb7302d8)
p_vaddr: ffffffffffffffff
p_paddr: 100000000
p_filesz: 1073741824 (40000000)
p_memsz: 1073741824 (40000000)
p_flags: 7 (PF_X|PF_W|PF_R)
p_align: 0
What that says is: for the range of physical memory starting
at 0x100000000 (p_paddr), the vmcore contains a block of
memory starting at file offset (p_offset) 3144876760/0xbb7302d8
that is 1073741824/0x40000000 (p_filesz) bytes long.
More simply put, the 1GB of physical memory from 4GB to 5GB
can be found in the vmcore file starting at file offset 3144876760.
So if a request for physical memory page 0x100000000 comes
in, the crash utility reads from vmcore file offset 3144876760.
If the next physical page were requested, i.e., at 0x100001000,
it would read from vmcore file offset 3144876760+4096. It's
as simple as that -- so when you suggest that "crash is looking
in the wrong place for it", well, there's nothing that the
crash utility can do differently.
Now, back to the test sequence:
---Live system---
KERNEL: vmlinux-devcrash
DUMPFILE: /dev/crash
CPUS: 2
DATE: Tue Oct 14 16:08:28 2008
UPTIME: 00:02:07
LOAD AVERAGE: 0.17, 0.08, 0.03
TASKS: 97
NODENAME: test-machine
RELEASE: 2.6.20-17.39-custom2
VERSION: #1 SMP Tue Oct 14 13:45:17 PDT 2008
MACHINE: i686 (2200 Mhz)
MEMORY: 5 GB
PID: 5628
COMMAND: "crash"
TASK: 5d4c2560 [THREAD_INFO: f3de6000]
CPU: 1
STATE: TASK_RUNNING (ACTIVE)
crash> p modules
modules = $2 = {
next = 0xf8a3ea04,
prev = 0xf8842104
}
crash> module 0xf8a3ea00
struct module {
state = MODULE_STATE_LIVE,
list = {
next = 0xf8d10484,
prev = 0x403c63a4
},
name =
"crash\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\
000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\
000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000",
mkobj = {
kobj = {
k_name = 0xf8a3ea4c "crash",
name =
"crash\000\000\000\000\000\000\000\000\000\000\000\000\000\000",
kref = {
refcount = {
counter = 3
}
},
entry = {
next = 0x403c6068,
prev = 0xf8d104e4
},
parent = 0x403c6074
...
crash> vtop 0xf8a3ea00
VIRTUAL PHYSICAL
f8a3ea00 116017a00
OK -- so the physical memory location of the module data structure
is at physical address 116017a00, but...
PAGE DIRECTORY: 4044b000
PGD: 4044b018 => 6001
PMD: 6e28 => 1d51a067
PTE: 1d51a1f0 => 116017163
PAGE: 116017000
PTE PHYSICAL FLAGS
116017163 116017000 (PRESENT|RW|ACCESSED|DIRTY|GLOBAL)
PAGE PHYSICAL MAPPING INDEX CNT FLAGS
472c02e0 116017000 0 229173 1 80000000
You're reading from the beginning of the page, i.e., 116017000
instead of where the module structure is at 116017a00:
crash> rd -p 116017000 30
116017000: 53e58955 d089c389 4d8bca89 74c98508 U..S.......M...t
116017010: 01e9831f b85b0d74 ffffffea ffffba5d ....t.[.....]...
116017020: 03c3ffff 53132043 26b48d24 00000000 ....C .S$..&....
116017030: 89204389 5d5b2453 26b48dc3 00000000 .C .S$[]...&....
116017040: 83e58955 55892cec 08558be4 89f45d89 U....,.U..U..]..
116017050: 7d89f875 ffeabffc 4d89ffff 8b028be0 u..}.......M....
116017060: c3890452 ac0fd689 45890cf3 0ceec1ec R..........E....
116017070: 5589c889 89d231f0 ...U.1..
crash>
So therefore you're not seeing the "crash" strings embedded in
the raw physical data. Now, although it would have been "nice"
if you could have shown the contents of the module structure via
the physical address, the fact remains that since you used the
/dev/crash driver, the "module 0xf8a3ea00" command required that
the crash utility first translate the vmalloc address into its
physical equivalent, and then read from there.
In any case, you do have a dump of physical memory from 116017000
which at least is in the same 4k page as the module data structure,
so it should not change when read from the dumpfile.
> ---Using dump file---
>
>
> please wait... (gathering module symbol data)
> WARNING: cannot access vmalloc'd module memory
>
> KERNEL: vmlinux-devcrash
> DUMPFILE: /var/crash/vmcore
> CPUS: 2
> DATE: Tue Oct 14 16:09:32 2008
> UPTIME: 00:03:12
> LOAD AVERAGE: 0.09, 0.08, 0.02
> TASKS: 97
> NODENAME: test-machine
> RELEASE: 2.6.20-17.39-custom2
> VERSION: #1 SMP Tue Oct 14 13:45:17 PDT 2008
> MACHINE: i686 (2200 Mhz)
> MEMORY: 5 GB
> PANIC: "[ 192.148000] SysRq : Trigger a crashdump"
> PID: 0
> COMMAND: "swapper"
> TASK: 403c0440 (1 of 2) [THREAD_INFO: 403f2000]
> CPU: 0
> STATE: TASK_RUNNING (SYSRQ)
>
> crash> p modules
> modules = $2 = {
> next = 0xf8a3ea04,
> prev = 0xf8842104
> }
>
> crash> module 0xf8a3ea00
> struct module {
> state = MODULE_STATE_LIVE,
> list = {
> next = 0x0,
> prev = 0x0
> },
> name =
> "\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\0
> 00\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\0
> 00\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\0
> 00\000",
> mkobj = {
> kobj = {
> k_name = 0x0,
> name =
> "\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\0
> 00\000\000",
> kref = {
> refcount = {
> counter = 0
> }
> },
> entry = {
> next = 0x0,
> prev = 0x0
> ...
>
> crash> vtop 0xf8a3ea00
> VIRTUAL PHYSICAL
> f8a3ea00 116017a00
PAGE DIRECTORY: 4044b000
PGD: 4044b018 => 6001
PMD: 6e28 => 1d51a067
PTE: 1d51a1f0 => 116017163
PAGE: 116017000
PTE PHYSICAL FLAGS
116017163 116017000 (PRESENT|RW|ACCESSED|DIRTY|GLOBAL)
PAGE PHYSICAL MAPPING INDEX CNT FLAGS
472c02e0 116017000 0 229173 1 80000000
> crash> rd -p 116017000 30
> 116017000: 00000000 00000000 00000000 00000000 ................
> 116017010: 00000000 00000000 00000000 00000000 ................
> 116017020: 00000000 00000000 00000000 00000000 ................
> 116017030: 00000000 00000000 00000000 00000000 ................
> 116017040: 00000000 00000000 00000000 00000000 ................
> 116017050: 00000000 00000000 00000000 00000000 ................
> 116017060: 00000000 00000000 00000000 00000000 ................
> 116017070: 00000000 00000000 ........
> crash>
Now we're reading the same physical address as you did on
the dumpfile, and it's returning all zeroes. And the
"module 0xf8a3ea00" above shows all zeroes from a higher
location in the page because the same vmalloc translation is
done to turn it into a physical address before reading it
from the vmcore file. But instead of using the /dev/crash driver
to access the translated physical memory, the crash utility
uses the information from the ELF header's PT_LOAD segments
to find out where to find the page data in the vmcore file.
So, anyway, the "rd -p 116017000 30" command that you did
on both the live system and the dumpfile should yield the same
data.
It seems like in all examples to date, the file data read
at the greater-than-4GB PT_LOAD segment returns zeroes.
You can verify this from the crash utility's viewpoint by
doing a "help -n" during runtime when running with the dumpfile,
which will show you both the actual contents of the ELF header,
as well as the manner in which the PT_LOAD data is stored for
its use. (It's also shown with the "crash -d7 ..." output).
So again, from your original "crash.log" file, here is what the
ELF header's PT_LOAD segment contains:
Elf64_Phdr:
p_type: 1 (PT_LOAD)
p_offset: 3144876760 (bb7302d8)
p_vaddr: ffffffffffffffff
p_paddr: 100000000
p_filesz: 1073741824 (40000000)
p_memsz: 1073741824 (40000000)
p_flags: 7 (PF_X|PF_W|PF_R)
p_align: 0
And this is what the crash utility stored in its internal
data structure for that particular segment:
pt_load_segment[4]:
file_offset: bb7302d8
phys_start: 100000000
phys_end: 140000000
zero_fill: 0
And when the physical memory read request comes in, it filters
to this part of the crash utility's read_netdump() function in
netdump.c:
for (i = offset = 0; i < nd->num_pt_load_segments; i++) {
pls = &nd->pt_load_segments[i];
if ((paddr >= pls->phys_start) &&
(paddr < pls->phys_end)) {
offset = (off_t)(paddr - pls->phys_start) +
pls->file_offset;
break;
}
if (pls->zero_fill && (paddr >= pls->phys_end)
&&
(paddr < pls->zero_fill)) {
memset(bufptr, 0, cnt);
return cnt;
}
}
So for any physical address request between 100000000 to 140000000,
(4GB to 5GB) it will calculate the offset to seek to by subtracting
100000000 from the incoming physical address, and adding the difference
to the starting file offset of the whole segment.
So if you wanted to, you could put debug code just prior to the "break" above
that shows the pls->file_offset for a given incoming physical address.
But this code has been in place forever, so it's hard to conceive that
somehow it's not working in the case of this dumpfile. But presuming that
it *does* go to the correct file offset location in the vmcore, and it's
getting bogus data from there, then there's nothing that the crash
utility can do about it.
Dave
4:30 p.m.
New subject: "cannot access vmalloc'd module memory" when loading kdump'ed vmcore in crash
So Dave, at this am I correct in the assumption that it sounds like this is not a problem
with crash, but with the dump file itself? I tried one more go at modifying the
kexec-tools to have the correct PAGE_OFFSET defined and still got the same type of results
(all zeroes at the module's address), so that doesn't seem to be it.
Maybe this is a better question to take to the kexec mailing list, but do you know where
the line is drawn between the kernel support or the userspace (kexec-tools)? I'm
presuming that the kernel support is tied to each kernel (i.e. since I'm on 2.6.20
this issue could have been resolved in a more recent kernel). I'm wondering if I can
pull a newer kexec-tools and that they might work with 2.6.20 and possibly have this issue
resolved.
-Kevin
-----Original Message-----
From: crash-utility-bounces(a)redhat.com [mailto:crash-utility-bounces@redhat.com] On Behalf
Of Dave Anderson
Sent: Wednesday, October 15, 2008 6:53 AM
To: Discussion list for crash utility usage, maintenance and development
Subject: Re: [Crash-utility] "cannot access vmalloc'd module memory" when
loading kdump'ed vmcore in crash
----- "Kevin Worth" <kevin.worth(a)hp.com> wrote:
Hi Dave,
Before you responded I noticed that a simple "make modules" didn't
work because my kernel wasn't exporting the symbol. Rather than do
anything risky/complex which might risk mucking up the troubleshooting
process, I just rebuilt the kernel. It built just fine and now I can
load crash and I see "DUMPFILE: /dev/crash" when I load up crash. Let
me try walking through the steps that you had me do previously, this
time using /dev/crash instead of /dev/mem and /dev/kmem
You made one small error (but not totally fatal) in the suggested steps.
See my comments below...
>From my limited understanding of what's going on here, it would
appear that the dump file is missing some data, or else crash is
looking in the wrong place for it.
The crash utility is a slave to what is indicated in the PT_LOAD
segments of the ELF header of the kdump vmcore. In the case of
the physical memory chunk that starts at 4GB physical on your machine,
this is what's in the ELF header (from your original "crash.log" file):
Elf64_Phdr:
p_type: 1 (PT_LOAD)
p_offset: 3144876760 (bb7302d8)
p_vaddr: ffffffffffffffff
p_paddr: 100000000
p_filesz: 1073741824 (40000000)
p_memsz: 1073741824 (40000000)
p_flags: 7 (PF_X|PF_W|PF_R)
p_align: 0
What that says is: for the range of physical memory starting
at 0x100000000 (p_paddr), the vmcore contains a block of
memory starting at file offset (p_offset) 3144876760/0xbb7302d8
that is 1073741824/0x40000000 (p_filesz) bytes long.
More simply put, the 1GB of physical memory from 4GB to 5GB
can be found in the vmcore file starting at file offset 3144876760.
So if a request for physical memory page 0x100000000 comes
in, the crash utility reads from vmcore file offset 3144876760.
If the next physical page were requested, i.e., at 0x100001000,
it would read from vmcore file offset 3144876760+4096. It's
as simple as that -- so when you suggest that "crash is looking
in the wrong place for it", well, there's nothing that the
crash utility can do differently.
Now, back to the test sequence:
---Live system---
KERNEL: vmlinux-devcrash
DUMPFILE: /dev/crash
CPUS: 2
DATE: Tue Oct 14 16:08:28 2008
UPTIME: 00:02:07
LOAD AVERAGE: 0.17, 0.08, 0.03
TASKS: 97
NODENAME: test-machine
RELEASE: 2.6.20-17.39-custom2
VERSION: #1 SMP Tue Oct 14 13:45:17 PDT 2008
MACHINE: i686 (2200 Mhz)
MEMORY: 5 GB
PID: 5628
COMMAND: "crash"
TASK: 5d4c2560 [THREAD_INFO: f3de6000]
CPU: 1
STATE: TASK_RUNNING (ACTIVE)
crash> p modules
modules = $2 = {
next = 0xf8a3ea04,
prev = 0xf8842104
}
crash> module 0xf8a3ea00
struct module {
state = MODULE_STATE_LIVE,
list = {
next = 0xf8d10484,
prev = 0x403c63a4
},
name =
"crash\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\
000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\
000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000",
mkobj = {
kobj = {
k_name = 0xf8a3ea4c "crash",
name =
"crash\000\000\000\000\000\000\000\000\000\000\000\000\000\000",
kref = {
refcount = {
counter = 3
}
},
entry = {
next = 0x403c6068,
prev = 0xf8d104e4
},
parent = 0x403c6074
...
crash> vtop 0xf8a3ea00
VIRTUAL PHYSICAL
f8a3ea00 116017a00
OK -- so the physical memory location of the module data structure
is at physical address 116017a00, but...
PAGE DIRECTORY: 4044b000
PGD: 4044b018 => 6001
PMD: 6e28 => 1d51a067
PTE: 1d51a1f0 => 116017163
PAGE: 116017000
PTE PHYSICAL FLAGS
116017163 116017000 (PRESENT|RW|ACCESSED|DIRTY|GLOBAL)
PAGE PHYSICAL MAPPING INDEX CNT FLAGS
472c02e0 116017000 0 229173 1 80000000
You're reading from the beginning of the page, i.e., 116017000
instead of where the module structure is at 116017a00:
crash> rd -p 116017000 30
116017000: 53e58955 d089c389 4d8bca89 74c98508 U..S.......M...t
116017010: 01e9831f b85b0d74 ffffffea ffffba5d ....t.[.....]...
116017020: 03c3ffff 53132043 26b48d24 00000000 ....C .S$..&....
116017030: 89204389 5d5b2453 26b48dc3 00000000 .C .S$[]...&....
116017040: 83e58955 55892cec 08558be4 89f45d89 U....,.U..U..]..
116017050: 7d89f875 ffeabffc 4d89ffff 8b028be0 u..}.......M....
116017060: c3890452 ac0fd689 45890cf3 0ceec1ec R..........E....
116017070: 5589c889 89d231f0 ...U.1..
crash>
So therefore you're not seeing the "crash" strings embedded in
the raw physical data. Now, although it would have been "nice"
if you could have shown the contents of the module structure via
the physical address, the fact remains that since you used the
/dev/crash driver, the "module 0xf8a3ea00" command required that
the crash utility first translate the vmalloc address into its
physical equivalent, and then read from there.
In any case, you do have a dump of physical memory from 116017000
which at least is in the same 4k page as the module data structure,
so it should not change when read from the dumpfile.
> ---Using dump file---
>
>
> please wait... (gathering module symbol data)
> WARNING: cannot access vmalloc'd module memory
>
> KERNEL: vmlinux-devcrash
> DUMPFILE: /var/crash/vmcore
> CPUS: 2
> DATE: Tue Oct 14 16:09:32 2008
> UPTIME: 00:03:12
> LOAD AVERAGE: 0.09, 0.08, 0.02
> TASKS: 97
> NODENAME: test-machine
> RELEASE: 2.6.20-17.39-custom2
> VERSION: #1 SMP Tue Oct 14 13:45:17 PDT 2008
> MACHINE: i686 (2200 Mhz)
> MEMORY: 5 GB
> PANIC: "[ 192.148000] SysRq : Trigger a crashdump"
> PID: 0
> COMMAND: "swapper"
> TASK: 403c0440 (1 of 2) [THREAD_INFO: 403f2000]
> CPU: 0
> STATE: TASK_RUNNING (SYSRQ)
>
> crash> p modules
> modules = $2 = {
> next = 0xf8a3ea04,
> prev = 0xf8842104
> }
>
> crash> module 0xf8a3ea00
> struct module {
> state = MODULE_STATE_LIVE,
> list = {
> next = 0x0,
> prev = 0x0
> },
> name =
> "\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\0
> 00\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\0
> 00\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\0
> 00\000",
> mkobj = {
> kobj = {
> k_name = 0x0,
> name =
> "\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\0
> 00\000\000",
> kref = {
> refcount = {
> counter = 0
> }
> },
> entry = {
> next = 0x0,
> prev = 0x0
> ...
>
> crash> vtop 0xf8a3ea00
> VIRTUAL PHYSICAL
> f8a3ea00 116017a00
PAGE DIRECTORY: 4044b000
PGD: 4044b018 => 6001
PMD: 6e28 => 1d51a067
PTE: 1d51a1f0 => 116017163
PAGE: 116017000
PTE PHYSICAL FLAGS
116017163 116017000 (PRESENT|RW|ACCESSED|DIRTY|GLOBAL)
PAGE PHYSICAL MAPPING INDEX CNT FLAGS
472c02e0 116017000 0 229173 1 80000000
> crash> rd -p 116017000 30
> 116017000: 00000000 00000000 00000000 00000000 ................
> 116017010: 00000000 00000000 00000000 00000000 ................
> 116017020: 00000000 00000000 00000000 00000000 ................
> 116017030: 00000000 00000000 00000000 00000000 ................
> 116017040: 00000000 00000000 00000000 00000000 ................
> 116017050: 00000000 00000000 00000000 00000000 ................
> 116017060: 00000000 00000000 00000000 00000000 ................
> 116017070: 00000000 00000000 ........
> crash>
Now we're reading the same physical address as you did on
the dumpfile, and it's returning all zeroes. And the
"module 0xf8a3ea00" above shows all zeroes from a higher
location in the page because the same vmalloc translation is
done to turn it into a physical address before reading it
from the vmcore file. But instead of using the /dev/crash driver
to access the translated physical memory, the crash utility
uses the information from the ELF header's PT_LOAD segments
to find out where to find the page data in the vmcore file.
So, anyway, the "rd -p 116017000 30" command that you did
on both the live system and the dumpfile should yield the same
data.
It seems like in all examples to date, the file data read
at the greater-than-4GB PT_LOAD segment returns zeroes.
You can verify this from the crash utility's viewpoint by
doing a "help -n" during runtime when running with the dumpfile,
which will show you both the actual contents of the ELF header,
as well as the manner in which the PT_LOAD data is stored for
its use. (It's also shown with the "crash -d7 ..." output).
So again, from your original "crash.log" file, here is what the
ELF header's PT_LOAD segment contains:
Elf64_Phdr:
p_type: 1 (PT_LOAD)
p_offset: 3144876760 (bb7302d8)
p_vaddr: ffffffffffffffff
p_paddr: 100000000
p_filesz: 1073741824 (40000000)
p_memsz: 1073741824 (40000000)
p_flags: 7 (PF_X|PF_W|PF_R)
p_align: 0
And this is what the crash utility stored in its internal
data structure for that particular segment:
pt_load_segment[4]:
file_offset: bb7302d8
phys_start: 100000000
phys_end: 140000000
zero_fill: 0
And when the physical memory read request comes in, it filters
to this part of the crash utility's read_netdump() function in
netdump.c:
for (i = offset = 0; i < nd->num_pt_load_segments; i++) {
pls = &nd->pt_load_segments[i];
if ((paddr >= pls->phys_start) &&
(paddr < pls->phys_end)) {
offset = (off_t)(paddr - pls->phys_start) +
pls->file_offset;
break;
}
if (pls->zero_fill && (paddr >= pls->phys_end)
&&
(paddr < pls->zero_fill)) {
memset(bufptr, 0, cnt);
return cnt;
}
}
So for any physical address request between 100000000 to 140000000,
(4GB to 5GB) it will calculate the offset to seek to by subtracting
100000000 from the incoming physical address, and adding the difference
to the starting file offset of the whole segment.
So if you wanted to, you could put debug code just prior to the "break" above
that shows the pls->file_offset for a given incoming physical address.
But this code has been in place forever, so it's hard to conceive that
somehow it's not working in the case of this dumpfile. But presuming that
it *does* go to the correct file offset location in the vmcore, and it's
getting bogus data from there, then there's nothing that the crash
utility can do about it.
Dave
--
Crash-utility mailing list
Crash-utility(a)redhat.com
https://www.redhat.com/mailman/listinfo/crash-utility
4:42 p.m.
New subject: "cannot access vmalloc'd module memory" when loading kdump'ed vmcore in crash
Sorry please ignore the second paragraph... I am already running the most recent version
in Ubuntu, 20070330 from Simon Horman's kexec-tools-testing and kernel 2.6.20. ... may
try a newer version of kexec-tools-testing to see if anything changes.
-Kevin
-----Original Message-----
From: Worth, Kevin
Sent: Wednesday, October 15, 2008 2:31 PM
To: Discussion list for crash utility usage, maintenance and development
Subject: RE: [Crash-utility] "cannot access vmalloc'd module memory" when
loading kdump'ed vmcore in crash
So Dave, at this am I correct in the assumption that it sounds like this is not a problem
with crash, but with the dump file itself? I tried one more go at modifying the
kexec-tools to have the correct PAGE_OFFSET defined and still got the same type of results
(all zeroes at the module's address), so that doesn't seem to be it.
Maybe this is a better question to take to the kexec mailing list, but do you know where
the line is drawn between the kernel support or the userspace (kexec-tools)? I'm
presuming that the kernel support is tied to each kernel (i.e. since I'm on 2.6.20
this issue could have been resolved in a more recent kernel). I'm wondering if I can
pull a newer kexec-tools and that they might work with 2.6.20 and possibly have this issue
resolved.
-Kevin
-----Original Message-----
From: crash-utility-bounces(a)redhat.com [mailto:crash-utility-bounces@redhat.com] On Behalf
Of Dave Anderson
Sent: Wednesday, October 15, 2008 6:53 AM
To: Discussion list for crash utility usage, maintenance and development
Subject: Re: [Crash-utility] "cannot access vmalloc'd module memory" when
loading kdump'ed vmcore in crash
----- "Kevin Worth" <kevin.worth(a)hp.com> wrote:
Hi Dave,
Before you responded I noticed that a simple "make modules" didn't
work because my kernel wasn't exporting the symbol. Rather than do
anything risky/complex which might risk mucking up the troubleshooting
process, I just rebuilt the kernel. It built just fine and now I can
load crash and I see "DUMPFILE: /dev/crash" when I load up crash. Let
me try walking through the steps that you had me do previously, this
time using /dev/crash instead of /dev/mem and /dev/kmem
You made one small error (but not totally fatal) in the suggested steps.
See my comments below...
>From my limited understanding of what's going on here, it would
appear that the dump file is missing some data, or else crash is
looking in the wrong place for it.
The crash utility is a slave to what is indicated in the PT_LOAD
segments of the ELF header of the kdump vmcore. In the case of
the physical memory chunk that starts at 4GB physical on your machine,
this is what's in the ELF header (from your original "crash.log" file):
Elf64_Phdr:
p_type: 1 (PT_LOAD)
p_offset: 3144876760 (bb7302d8)
p_vaddr: ffffffffffffffff
p_paddr: 100000000
p_filesz: 1073741824 (40000000)
p_memsz: 1073741824 (40000000)
p_flags: 7 (PF_X|PF_W|PF_R)
p_align: 0
What that says is: for the range of physical memory starting
at 0x100000000 (p_paddr), the vmcore contains a block of
memory starting at file offset (p_offset) 3144876760/0xbb7302d8
that is 1073741824/0x40000000 (p_filesz) bytes long.
More simply put, the 1GB of physical memory from 4GB to 5GB
can be found in the vmcore file starting at file offset 3144876760.
So if a request for physical memory page 0x100000000 comes
in, the crash utility reads from vmcore file offset 3144876760.
If the next physical page were requested, i.e., at 0x100001000,
it would read from vmcore file offset 3144876760+4096. It's
as simple as that -- so when you suggest that "crash is looking
in the wrong place for it", well, there's nothing that the
crash utility can do differently.
Now, back to the test sequence:
---Live system---
KERNEL: vmlinux-devcrash
DUMPFILE: /dev/crash
CPUS: 2
DATE: Tue Oct 14 16:08:28 2008
UPTIME: 00:02:07
LOAD AVERAGE: 0.17, 0.08, 0.03
TASKS: 97
NODENAME: test-machine
RELEASE: 2.6.20-17.39-custom2
VERSION: #1 SMP Tue Oct 14 13:45:17 PDT 2008
MACHINE: i686 (2200 Mhz)
MEMORY: 5 GB
PID: 5628
COMMAND: "crash"
TASK: 5d4c2560 [THREAD_INFO: f3de6000]
CPU: 1
STATE: TASK_RUNNING (ACTIVE)
crash> p modules
modules = $2 = {
next = 0xf8a3ea04,
prev = 0xf8842104
}
crash> module 0xf8a3ea00
struct module {
state = MODULE_STATE_LIVE,
list = {
next = 0xf8d10484,
prev = 0x403c63a4
},
name =
"crash\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\
000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\
000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000",
mkobj = {
kobj = {
k_name = 0xf8a3ea4c "crash",
name =
"crash\000\000\000\000\000\000\000\000\000\000\000\000\000\000",
kref = {
refcount = {
counter = 3
}
},
entry = {
next = 0x403c6068,
prev = 0xf8d104e4
},
parent = 0x403c6074
...
crash> vtop 0xf8a3ea00
VIRTUAL PHYSICAL
f8a3ea00 116017a00
OK -- so the physical memory location of the module data structure
is at physical address 116017a00, but...
PAGE DIRECTORY: 4044b000
PGD: 4044b018 => 6001
PMD: 6e28 => 1d51a067
PTE: 1d51a1f0 => 116017163
PAGE: 116017000
PTE PHYSICAL FLAGS
116017163 116017000 (PRESENT|RW|ACCESSED|DIRTY|GLOBAL)
PAGE PHYSICAL MAPPING INDEX CNT FLAGS
472c02e0 116017000 0 229173 1 80000000
You're reading from the beginning of the page, i.e., 116017000
instead of where the module structure is at 116017a00:
crash> rd -p 116017000 30
116017000: 53e58955 d089c389 4d8bca89 74c98508 U..S.......M...t
116017010: 01e9831f b85b0d74 ffffffea ffffba5d ....t.[.....]...
116017020: 03c3ffff 53132043 26b48d24 00000000 ....C .S$..&....
116017030: 89204389 5d5b2453 26b48dc3 00000000 .C .S$[]...&....
116017040: 83e58955 55892cec 08558be4 89f45d89 U....,.U..U..]..
116017050: 7d89f875 ffeabffc 4d89ffff 8b028be0 u..}.......M....
116017060: c3890452 ac0fd689 45890cf3 0ceec1ec R..........E....
116017070: 5589c889 89d231f0 ...U.1..
crash>
So therefore you're not seeing the "crash" strings embedded in
the raw physical data. Now, although it would have been "nice"
if you could have shown the contents of the module structure via
the physical address, the fact remains that since you used the
/dev/crash driver, the "module 0xf8a3ea00" command required that
the crash utility first translate the vmalloc address into its
physical equivalent, and then read from there.
In any case, you do have a dump of physical memory from 116017000
which at least is in the same 4k page as the module data structure,
so it should not change when read from the dumpfile.
> ---Using dump file---
>
>
> please wait... (gathering module symbol data)
> WARNING: cannot access vmalloc'd module memory
>
> KERNEL: vmlinux-devcrash
> DUMPFILE: /var/crash/vmcore
> CPUS: 2
> DATE: Tue Oct 14 16:09:32 2008
> UPTIME: 00:03:12
> LOAD AVERAGE: 0.09, 0.08, 0.02
> TASKS: 97
> NODENAME: test-machine
> RELEASE: 2.6.20-17.39-custom2
> VERSION: #1 SMP Tue Oct 14 13:45:17 PDT 2008
> MACHINE: i686 (2200 Mhz)
> MEMORY: 5 GB
> PANIC: "[ 192.148000] SysRq : Trigger a crashdump"
> PID: 0
> COMMAND: "swapper"
> TASK: 403c0440 (1 of 2) [THREAD_INFO: 403f2000]
> CPU: 0
> STATE: TASK_RUNNING (SYSRQ)
>
> crash> p modules
> modules = $2 = {
> next = 0xf8a3ea04,
> prev = 0xf8842104
> }
>
> crash> module 0xf8a3ea00
> struct module {
> state = MODULE_STATE_LIVE,
> list = {
> next = 0x0,
> prev = 0x0
> },
> name =
> "\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\0
> 00\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\0
> 00\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\0
> 00\000",
> mkobj = {
> kobj = {
> k_name = 0x0,
> name =
> "\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\0
> 00\000\000",
> kref = {
> refcount = {
> counter = 0
> }
> },
> entry = {
> next = 0x0,
> prev = 0x0
> ...
>
> crash> vtop 0xf8a3ea00
> VIRTUAL PHYSICAL
> f8a3ea00 116017a00
PAGE DIRECTORY: 4044b000
PGD: 4044b018 => 6001
PMD: 6e28 => 1d51a067
PTE: 1d51a1f0 => 116017163
PAGE: 116017000
PTE PHYSICAL FLAGS
116017163 116017000 (PRESENT|RW|ACCESSED|DIRTY|GLOBAL)
PAGE PHYSICAL MAPPING INDEX CNT FLAGS
472c02e0 116017000 0 229173 1 80000000
> crash> rd -p 116017000 30
> 116017000: 00000000 00000000 00000000 00000000 ................
> 116017010: 00000000 00000000 00000000 00000000 ................
> 116017020: 00000000 00000000 00000000 00000000 ................
> 116017030: 00000000 00000000 00000000 00000000 ................
> 116017040: 00000000 00000000 00000000 00000000 ................
> 116017050: 00000000 00000000 00000000 00000000 ................
> 116017060: 00000000 00000000 00000000 00000000 ................
> 116017070: 00000000 00000000 ........
> crash>
Now we're reading the same physical address as you did on
the dumpfile, and it's returning all zeroes. And the
"module 0xf8a3ea00" above shows all zeroes from a higher
location in the page because the same vmalloc translation is
done to turn it into a physical address before reading it
from the vmcore file. But instead of using the /dev/crash driver
to access the translated physical memory, the crash utility
uses the information from the ELF header's PT_LOAD segments
to find out where to find the page data in the vmcore file.
So, anyway, the "rd -p 116017000 30" command that you did
on both the live system and the dumpfile should yield the same
data.
It seems like in all examples to date, the file data read
at the greater-than-4GB PT_LOAD segment returns zeroes.
You can verify this from the crash utility's viewpoint by
doing a "help -n" during runtime when running with the dumpfile,
which will show you both the actual contents of the ELF header,
as well as the manner in which the PT_LOAD data is stored for
its use. (It's also shown with the "crash -d7 ..." output).
So again, from your original "crash.log" file, here is what the
ELF header's PT_LOAD segment contains:
Elf64_Phdr:
p_type: 1 (PT_LOAD)
p_offset: 3144876760 (bb7302d8)
p_vaddr: ffffffffffffffff
p_paddr: 100000000
p_filesz: 1073741824 (40000000)
p_memsz: 1073741824 (40000000)
p_flags: 7 (PF_X|PF_W|PF_R)
p_align: 0
And this is what the crash utility stored in its internal
data structure for that particular segment:
pt_load_segment[4]:
file_offset: bb7302d8
phys_start: 100000000
phys_end: 140000000
zero_fill: 0
And when the physical memory read request comes in, it filters
to this part of the crash utility's read_netdump() function in
netdump.c:
for (i = offset = 0; i < nd->num_pt_load_segments; i++) {
pls = &nd->pt_load_segments[i];
if ((paddr >= pls->phys_start) &&
(paddr < pls->phys_end)) {
offset = (off_t)(paddr - pls->phys_start) +
pls->file_offset;
break;
}
if (pls->zero_fill && (paddr >= pls->phys_end)
&&
(paddr < pls->zero_fill)) {
memset(bufptr, 0, cnt);
return cnt;
}
}
So for any physical address request between 100000000 to 140000000,
(4GB to 5GB) it will calculate the offset to seek to by subtracting
100000000 from the incoming physical address, and adding the difference
to the starting file offset of the whole segment.
So if you wanted to, you could put debug code just prior to the "break" above
that shows the pls->file_offset for a given incoming physical address.
But this code has been in place forever, so it's hard to conceive that
somehow it's not working in the case of this dumpfile. But presuming that
it *does* go to the correct file offset location in the vmcore, and it's
getting bogus data from there, then there's nothing that the crash
utility can do about it.
Dave
--
Crash-utility mailing list
Crash-utility(a)redhat.com
https://www.redhat.com/mailman/listinfo/crash-utility
6:16 p.m.
New subject: "cannot access vmalloc'd module memory" when loading kdump'ed vmcore in crash
Tried version 2.0 of kexec-tools (released 7/19/2008) and still have the same problem with
zero'ed out module info. Sounds like perhaps it is narrowed down to the 2.6.20 kernel
kdump code (the most difficult part to change out, but the part that likely gets a lot of
eyes on it and probably has the issue fixed in current versions). :\
-Kevin
-----Original Message-----
From: crash-utility-bounces(a)redhat.com [mailto:crash-utility-bounces@redhat.com] On Behalf
Of Worth, Kevin
Sent: Wednesday, October 15, 2008 2:43 PM
To: Discussion list for crash utility usage, maintenance and development
Subject: RE: [Crash-utility] "cannot access vmalloc'd module memory" when
loading kdump'ed vmcore in crash
Sorry please ignore the second paragraph... I am already running the most recent version
in Ubuntu, 20070330 from Simon Horman's kexec-tools-testing and kernel 2.6.20. ... may
try a newer version of kexec-tools-testing to see if anything changes.
-Kevin
-----Original Message-----
From: Worth, Kevin
Sent: Wednesday, October 15, 2008 2:31 PM
To: Discussion list for crash utility usage, maintenance and development
Subject: RE: [Crash-utility] "cannot access vmalloc'd module memory" when
loading kdump'ed vmcore in crash
So Dave, at this am I correct in the assumption that it sounds like this is not a problem
with crash, but with the dump file itself? I tried one more go at modifying the
kexec-tools to have the correct PAGE_OFFSET defined and still got the same type of results
(all zeroes at the module's address), so that doesn't seem to be it.
Maybe this is a better question to take to the kexec mailing list, but do you know where
the line is drawn between the kernel support or the userspace (kexec-tools)? I'm
presuming that the kernel support is tied to each kernel (i.e. since I'm on 2.6.20
this issue could have been resolved in a more recent kernel). I'm wondering if I can
pull a newer kexec-tools and that they might work with 2.6.20 and possibly have this issue
resolved.
-Kevin
-----Original Message-----
From: crash-utility-bounces(a)redhat.com [mailto:crash-utility-bounces@redhat.com] On Behalf
Of Dave Anderson
Sent: Wednesday, October 15, 2008 6:53 AM
To: Discussion list for crash utility usage, maintenance and development
Subject: Re: [Crash-utility] "cannot access vmalloc'd module memory" when
loading kdump'ed vmcore in crash
----- "Kevin Worth" <kevin.worth(a)hp.com> wrote:
Hi Dave,
Before you responded I noticed that a simple "make modules" didn't
work because my kernel wasn't exporting the symbol. Rather than do
anything risky/complex which might risk mucking up the troubleshooting
process, I just rebuilt the kernel. It built just fine and now I can
load crash and I see "DUMPFILE: /dev/crash" when I load up crash. Let
me try walking through the steps that you had me do previously, this
time using /dev/crash instead of /dev/mem and /dev/kmem
You made one small error (but not totally fatal) in the suggested steps.
See my comments below...
>From my limited understanding of what's going on here, it would
appear that the dump file is missing some data, or else crash is
looking in the wrong place for it.
The crash utility is a slave to what is indicated in the PT_LOAD
segments of the ELF header of the kdump vmcore. In the case of
the physical memory chunk that starts at 4GB physical on your machine,
this is what's in the ELF header (from your original "crash.log" file):
Elf64_Phdr:
p_type: 1 (PT_LOAD)
p_offset: 3144876760 (bb7302d8)
p_vaddr: ffffffffffffffff
p_paddr: 100000000
p_filesz: 1073741824 (40000000)
p_memsz: 1073741824 (40000000)
p_flags: 7 (PF_X|PF_W|PF_R)
p_align: 0
What that says is: for the range of physical memory starting
at 0x100000000 (p_paddr), the vmcore contains a block of
memory starting at file offset (p_offset) 3144876760/0xbb7302d8
that is 1073741824/0x40000000 (p_filesz) bytes long.
More simply put, the 1GB of physical memory from 4GB to 5GB
can be found in the vmcore file starting at file offset 3144876760.
So if a request for physical memory page 0x100000000 comes
in, the crash utility reads from vmcore file offset 3144876760.
If the next physical page were requested, i.e., at 0x100001000,
it would read from vmcore file offset 3144876760+4096. It's
as simple as that -- so when you suggest that "crash is looking
in the wrong place for it", well, there's nothing that the
crash utility can do differently.
Now, back to the test sequence:
---Live system---
KERNEL: vmlinux-devcrash
DUMPFILE: /dev/crash
CPUS: 2
DATE: Tue Oct 14 16:08:28 2008
UPTIME: 00:02:07
LOAD AVERAGE: 0.17, 0.08, 0.03
TASKS: 97
NODENAME: test-machine
RELEASE: 2.6.20-17.39-custom2
VERSION: #1 SMP Tue Oct 14 13:45:17 PDT 2008
MACHINE: i686 (2200 Mhz)
MEMORY: 5 GB
PID: 5628
COMMAND: "crash"
TASK: 5d4c2560 [THREAD_INFO: f3de6000]
CPU: 1
STATE: TASK_RUNNING (ACTIVE)
crash> p modules
modules = $2 = {
next = 0xf8a3ea04,
prev = 0xf8842104
}
crash> module 0xf8a3ea00
struct module {
state = MODULE_STATE_LIVE,
list = {
next = 0xf8d10484,
prev = 0x403c63a4
},
name =
"crash\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\
000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\
000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000",
mkobj = {
kobj = {
k_name = 0xf8a3ea4c "crash",
name =
"crash\000\000\000\000\000\000\000\000\000\000\000\000\000\000",
kref = {
refcount = {
counter = 3
}
},
entry = {
next = 0x403c6068,
prev = 0xf8d104e4
},
parent = 0x403c6074
...
crash> vtop 0xf8a3ea00
VIRTUAL PHYSICAL
f8a3ea00 116017a00
OK -- so the physical memory location of the module data structure
is at physical address 116017a00, but...
PAGE DIRECTORY: 4044b000
PGD: 4044b018 => 6001
PMD: 6e28 => 1d51a067
PTE: 1d51a1f0 => 116017163
PAGE: 116017000
PTE PHYSICAL FLAGS
116017163 116017000 (PRESENT|RW|ACCESSED|DIRTY|GLOBAL)
PAGE PHYSICAL MAPPING INDEX CNT FLAGS
472c02e0 116017000 0 229173 1 80000000
You're reading from the beginning of the page, i.e., 116017000
instead of where the module structure is at 116017a00:
crash> rd -p 116017000 30
116017000: 53e58955 d089c389 4d8bca89 74c98508 U..S.......M...t
116017010: 01e9831f b85b0d74 ffffffea ffffba5d ....t.[.....]...
116017020: 03c3ffff 53132043 26b48d24 00000000 ....C .S$..&....
116017030: 89204389 5d5b2453 26b48dc3 00000000 .C .S$[]...&....
116017040: 83e58955 55892cec 08558be4 89f45d89 U....,.U..U..]..
116017050: 7d89f875 ffeabffc 4d89ffff 8b028be0 u..}.......M....
116017060: c3890452 ac0fd689 45890cf3 0ceec1ec R..........E....
116017070: 5589c889 89d231f0 ...U.1..
crash>
So therefore you're not seeing the "crash" strings embedded in
the raw physical data. Now, although it would have been "nice"
if you could have shown the contents of the module structure via
the physical address, the fact remains that since you used the
/dev/crash driver, the "module 0xf8a3ea00" command required that
the crash utility first translate the vmalloc address into its
physical equivalent, and then read from there.
In any case, you do have a dump of physical memory from 116017000
which at least is in the same 4k page as the module data structure,
so it should not change when read from the dumpfile.
> ---Using dump file---
>
>
> please wait... (gathering module symbol data)
> WARNING: cannot access vmalloc'd module memory
>
> KERNEL: vmlinux-devcrash
> DUMPFILE: /var/crash/vmcore
> CPUS: 2
> DATE: Tue Oct 14 16:09:32 2008
> UPTIME: 00:03:12
> LOAD AVERAGE: 0.09, 0.08, 0.02
> TASKS: 97
> NODENAME: test-machine
> RELEASE: 2.6.20-17.39-custom2
> VERSION: #1 SMP Tue Oct 14 13:45:17 PDT 2008
> MACHINE: i686 (2200 Mhz)
> MEMORY: 5 GB
> PANIC: "[ 192.148000] SysRq : Trigger a crashdump"
> PID: 0
> COMMAND: "swapper"
> TASK: 403c0440 (1 of 2) [THREAD_INFO: 403f2000]
> CPU: 0
> STATE: TASK_RUNNING (SYSRQ)
>
> crash> p modules
> modules = $2 = {
> next = 0xf8a3ea04,
> prev = 0xf8842104
> }
>
> crash> module 0xf8a3ea00
> struct module {
> state = MODULE_STATE_LIVE,
> list = {
> next = 0x0,
> prev = 0x0
> },
> name =
> "\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\0
> 00\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\0
> 00\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\0
> 00\000",
> mkobj = {
> kobj = {
> k_name = 0x0,
> name =
> "\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\0
> 00\000\000",
> kref = {
> refcount = {
> counter = 0
> }
> },
> entry = {
> next = 0x0,
> prev = 0x0
> ...
>
> crash> vtop 0xf8a3ea00
> VIRTUAL PHYSICAL
> f8a3ea00 116017a00
PAGE DIRECTORY: 4044b000
PGD: 4044b018 => 6001
PMD: 6e28 => 1d51a067
PTE: 1d51a1f0 => 116017163
PAGE: 116017000
PTE PHYSICAL FLAGS
116017163 116017000 (PRESENT|RW|ACCESSED|DIRTY|GLOBAL)
PAGE PHYSICAL MAPPING INDEX CNT FLAGS
472c02e0 116017000 0 229173 1 80000000
> crash> rd -p 116017000 30
> 116017000: 00000000 00000000 00000000 00000000 ................
> 116017010: 00000000 00000000 00000000 00000000 ................
> 116017020: 00000000 00000000 00000000 00000000 ................
> 116017030: 00000000 00000000 00000000 00000000 ................
> 116017040: 00000000 00000000 00000000 00000000 ................
> 116017050: 00000000 00000000 00000000 00000000 ................
> 116017060: 00000000 00000000 00000000 00000000 ................
> 116017070: 00000000 00000000 ........
> crash>
Now we're reading the same physical address as you did on
the dumpfile, and it's returning all zeroes. And the
"module 0xf8a3ea00" above shows all zeroes from a higher
location in the page because the same vmalloc translation is
done to turn it into a physical address before reading it
from the vmcore file. But instead of using the /dev/crash driver
to access the translated physical memory, the crash utility
uses the information from the ELF header's PT_LOAD segments
to find out where to find the page data in the vmcore file.
So, anyway, the "rd -p 116017000 30" command that you did
on both the live system and the dumpfile should yield the same
data.
It seems like in all examples to date, the file data read
at the greater-than-4GB PT_LOAD segment returns zeroes.
You can verify this from the crash utility's viewpoint by
doing a "help -n" during runtime when running with the dumpfile,
which will show you both the actual contents of the ELF header,
as well as the manner in which the PT_LOAD data is stored for
its use. (It's also shown with the "crash -d7 ..." output).
So again, from your original "crash.log" file, here is what the
ELF header's PT_LOAD segment contains:
Elf64_Phdr:
p_type: 1 (PT_LOAD)
p_offset: 3144876760 (bb7302d8)
p_vaddr: ffffffffffffffff
p_paddr: 100000000
p_filesz: 1073741824 (40000000)
p_memsz: 1073741824 (40000000)
p_flags: 7 (PF_X|PF_W|PF_R)
p_align: 0
And this is what the crash utility stored in its internal
data structure for that particular segment:
pt_load_segment[4]:
file_offset: bb7302d8
phys_start: 100000000
phys_end: 140000000
zero_fill: 0
And when the physical memory read request comes in, it filters
to this part of the crash utility's read_netdump() function in
netdump.c:
for (i = offset = 0; i < nd->num_pt_load_segments; i++) {
pls = &nd->pt_load_segments[i];
if ((paddr >= pls->phys_start) &&
(paddr < pls->phys_end)) {
offset = (off_t)(paddr - pls->phys_start) +
pls->file_offset;
break;
}
if (pls->zero_fill && (paddr >= pls->phys_end)
&&
(paddr < pls->zero_fill)) {
memset(bufptr, 0, cnt);
return cnt;
}
}
So for any physical address request between 100000000 to 140000000,
(4GB to 5GB) it will calculate the offset to seek to by subtracting
100000000 from the incoming physical address, and adding the difference
to the starting file offset of the whole segment.
So if you wanted to, you could put debug code just prior to the "break" above
that shows the pls->file_offset for a given incoming physical address.
But this code has been in place forever, so it's hard to conceive that
somehow it's not working in the case of this dumpfile. But presuming that
it *does* go to the correct file offset location in the vmcore, and it's
getting bogus data from there, then there's nothing that the crash
utility can do about it.
Dave
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8:11 a.m.
New subject: "cannot access vmalloc'd module memory" when loading kdump'ed vmcore in crash
----- "Kevin Worth" <kevin.worth(a)hp.com> wrote:
Tried version 2.0 of kexec-tools (released 7/19/2008) and still have
the same problem with zero'ed out module info. Sounds like perhaps it
is narrowed down to the 2.6.20 kernel kdump code (the most difficult
part to change out, but the part that likely gets a lot of eyes on it
and probably has the issue fixed in current versions). :\
Certainly possible. From my understanding, the kexec tools piece on
the primary kernel side is mostly concerned with creating the proper
ELF headers for the second kernel to use when /proc/vmcore is read.
And aside from the bogus p_vaddr fields that were using the hardwired
c0000000 PAGE_OFFSET based values, things looked correct.
When the user-space code on the secondary kernel reads the /proc/vmcore
pseudo-file, the secondary kdump kernel dynamically kmaps and reads the
physical memory from the "oldmem" location, and copies it out to user-space.
Why it would read zeroed-out memory from those locations is hard to understand.
I was looking at the "fs/proc/vmcore.c" sources yesterday in our RHEL5
kernel (2.6.18 + patches) for something that could be a issue with the
1GB/3GB split, and also given that your secondary kdump kernel is
still a 3GB/1GB kernel (is that right?). But I couldn't see anything
there.
Dave
-Kevin
-----Original Message-----
From: crash-utility-bounces(a)redhat.com
[mailto:crash-utility-bounces@redhat.com] On Behalf Of Worth, Kevin
Sent: Wednesday, October 15, 2008 2:43 PM
To: Discussion list for crash utility usage, maintenance and
development
Subject: RE: [Crash-utility] "cannot access vmalloc'd module memory"
when loading kdump'ed vmcore in crash
Sorry please ignore the second paragraph... I am already running the
most recent version in Ubuntu, 20070330 from Simon Horman's
kexec-tools-testing and kernel 2.6.20. ... may try a newer version of
kexec-tools-testing to see if anything changes.
-Kevin
-----Original Message-----
From: Worth, Kevin
Sent: Wednesday, October 15, 2008 2:31 PM
To: Discussion list for crash utility usage, maintenance and
development
Subject: RE: [Crash-utility] "cannot access vmalloc'd module memory"
when loading kdump'ed vmcore in crash
So Dave, at this am I correct in the assumption that it sounds like
this is not a problem with crash, but with the dump file itself? I
tried one more go at modifying the kexec-tools to have the correct
PAGE_OFFSET defined and still got the same type of results (all zeroes
at the module's address), so that doesn't seem to be it.
Maybe this is a better question to take to the kexec mailing list, but
do you know where the line is drawn between the kernel support or the
userspace (kexec-tools)? I'm presuming that the kernel support is tied
to each kernel (i.e. since I'm on 2.6.20 this issue could have been
resolved in a more recent kernel). I'm wondering if I can pull a newer
kexec-tools and that they might work with 2.6.20 and possibly have
this issue resolved.
-Kevin
-----Original Message-----
From: crash-utility-bounces(a)redhat.com
[mailto:crash-utility-bounces@redhat.com] On Behalf Of Dave Anderson
Sent: Wednesday, October 15, 2008 6:53 AM
To: Discussion list for crash utility usage, maintenance and
development
Subject: Re: [Crash-utility] "cannot access vmalloc'd module memory"
when loading kdump'ed vmcore in crash
----- "Kevin Worth" <kevin.worth(a)hp.com> wrote:
> Hi Dave,
>
> Before you responded I noticed that a simple "make modules" didn't
> work because my kernel wasn't exporting the symbol. Rather than do
> anything risky/complex which might risk mucking up the
troubleshooting
> process, I just rebuilt the kernel. It built just fine and now I
can
> load crash and I see "DUMPFILE: /dev/crash" when I load up crash.
Let
> me try walking through the steps that you had me do previously,
this
> time using /dev/crash instead of /dev/mem and /dev/kmem
You made one small error (but not totally fatal) in the suggested
steps.
See my comments below...
>
> >From my limited understanding of what's going on here, it would
> appear that the dump file is missing some data, or else crash is
> looking in the wrong place for it.
The crash utility is a slave to what is indicated in the PT_LOAD
segments of the ELF header of the kdump vmcore. In the case of
the physical memory chunk that starts at 4GB physical on your
machine,
this is what's in the ELF header (from your original "crash.log"
file):
Elf64_Phdr:
p_type: 1 (PT_LOAD)
p_offset: 3144876760 (bb7302d8)
p_vaddr: ffffffffffffffff
p_paddr: 100000000
p_filesz: 1073741824 (40000000)
p_memsz: 1073741824 (40000000)
p_flags: 7 (PF_X|PF_W|PF_R)
p_align: 0
What that says is: for the range of physical memory starting
at 0x100000000 (p_paddr), the vmcore contains a block of
memory starting at file offset (p_offset) 3144876760/0xbb7302d8
that is 1073741824/0x40000000 (p_filesz) bytes long.
More simply put, the 1GB of physical memory from 4GB to 5GB
can be found in the vmcore file starting at file offset 3144876760.
So if a request for physical memory page 0x100000000 comes
in, the crash utility reads from vmcore file offset 3144876760.
If the next physical page were requested, i.e., at 0x100001000,
it would read from vmcore file offset 3144876760+4096. It's
as simple as that -- so when you suggest that "crash is looking
in the wrong place for it", well, there's nothing that the
crash utility can do differently.
Now, back to the test sequence:
> ---Live system---
>
> KERNEL: vmlinux-devcrash
> DUMPFILE: /dev/crash
> CPUS: 2
> DATE: Tue Oct 14 16:08:28 2008
> UPTIME: 00:02:07
> LOAD AVERAGE: 0.17, 0.08, 0.03
> TASKS: 97
> NODENAME: test-machine
> RELEASE: 2.6.20-17.39-custom2
> VERSION: #1 SMP Tue Oct 14 13:45:17 PDT 2008
> MACHINE: i686 (2200 Mhz)
> MEMORY: 5 GB
> PID: 5628
> COMMAND: "crash"
> TASK: 5d4c2560 [THREAD_INFO: f3de6000]
> CPU: 1
> STATE: TASK_RUNNING (ACTIVE)
>
> crash> p modules
> modules = $2 = {
> next = 0xf8a3ea04,
> prev = 0xf8842104
> }
>
> crash> module 0xf8a3ea00
> struct module {
> state = MODULE_STATE_LIVE,
> list = {
> next = 0xf8d10484,
> prev = 0x403c63a4
> },
> name =
>
"crash\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\
>
000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\
>
000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000",
> mkobj = {
> kobj = {
> k_name = 0xf8a3ea4c "crash",
> name =
> "crash\000\000\000\000\000\000\000\000\000\000\000\000\000\000",
> kref = {
> refcount = {
> counter = 3
> }
> },
> entry = {
> next = 0x403c6068,
> prev = 0xf8d104e4
> },
> parent = 0x403c6074
> ...
>
> crash> vtop 0xf8a3ea00
> VIRTUAL PHYSICAL
> f8a3ea00 116017a00
OK -- so the physical memory location of the module data structure
is at physical address 116017a00, but...
>
> PAGE DIRECTORY: 4044b000
> PGD: 4044b018 => 6001
> PMD: 6e28 => 1d51a067
> PTE: 1d51a1f0 => 116017163
> PAGE: 116017000
>
> PTE PHYSICAL FLAGS
> 116017163 116017000 (PRESENT|RW|ACCESSED|DIRTY|GLOBAL)
>
> PAGE PHYSICAL MAPPING INDEX CNT FLAGS
> 472c02e0 116017000 0 229173 1 80000000
>
You're reading from the beginning of the page, i.e., 116017000
instead of where the module structure is at 116017a00:
> crash> rd -p 116017000 30
> 116017000: 53e58955 d089c389 4d8bca89 74c98508 U..S.......M...t
> 116017010: 01e9831f b85b0d74 ffffffea ffffba5d ....t.[.....]...
> 116017020: 03c3ffff 53132043 26b48d24 00000000 ....C .S$..&....
> 116017030: 89204389 5d5b2453 26b48dc3 00000000 .C .S$[]...&....
> 116017040: 83e58955 55892cec 08558be4 89f45d89 U....,.U..U..]..
> 116017050: 7d89f875 ffeabffc 4d89ffff 8b028be0 u..}.......M....
> 116017060: c3890452 ac0fd689 45890cf3 0ceec1ec R..........E....
> 116017070: 5589c889 89d231f0 ...U.1..
> crash>
>
So therefore you're not seeing the "crash" strings embedded in
the raw physical data. Now, although it would have been "nice"
if you could have shown the contents of the module structure via
the physical address, the fact remains that since you used the
/dev/crash driver, the "module 0xf8a3ea00" command required that
the crash utility first translate the vmalloc address into its
physical equivalent, and then read from there.
In any case, you do have a dump of physical memory from 116017000
which at least is in the same 4k page as the module data structure,
so it should not change when read from the dumpfile.
> ---Using dump file---
>
>
> please wait... (gathering module symbol data)
> WARNING: cannot access vmalloc'd module memory
>
> KERNEL: vmlinux-devcrash
> DUMPFILE: /var/crash/vmcore
> CPUS: 2
> DATE: Tue Oct 14 16:09:32 2008
> UPTIME: 00:03:12
> LOAD AVERAGE: 0.09, 0.08, 0.02
> TASKS: 97
> NODENAME: test-machine
> RELEASE: 2.6.20-17.39-custom2
> VERSION: #1 SMP Tue Oct 14 13:45:17 PDT 2008
> MACHINE: i686 (2200 Mhz)
> MEMORY: 5 GB
> PANIC: "[ 192.148000] SysRq : Trigger a crashdump"
> PID: 0
> COMMAND: "swapper"
> TASK: 403c0440 (1 of 2) [THREAD_INFO: 403f2000]
> CPU: 0
> STATE: TASK_RUNNING (SYSRQ)
>
> crash> p modules
> modules = $2 = {
> next = 0xf8a3ea04,
> prev = 0xf8842104
> }
>
> crash> module 0xf8a3ea00
> struct module {
> state = MODULE_STATE_LIVE,
> list = {
> next = 0x0,
> prev = 0x0
> },
> name =
>
"\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\0
>
00\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\0
>
00\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\0
> 00\000",
> mkobj = {
> kobj = {
> k_name = 0x0,
> name =
> "\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\0
> 00\000\000",
> kref = {
> refcount = {
> counter = 0
> }
> },
> entry = {
> next = 0x0,
> prev = 0x0
> ...
>
> crash> vtop 0xf8a3ea00
> VIRTUAL PHYSICAL
> f8a3ea00 116017a00
>
> PAGE DIRECTORY: 4044b000
> PGD: 4044b018 => 6001
> PMD: 6e28 => 1d51a067
> PTE: 1d51a1f0 => 116017163
> PAGE: 116017000
>
> PTE PHYSICAL FLAGS
> 116017163 116017000 (PRESENT|RW|ACCESSED|DIRTY|GLOBAL)
>
> PAGE PHYSICAL MAPPING INDEX CNT FLAGS
> 472c02e0 116017000 0 229173 1 80000000
>
> crash> rd -p 116017000 30
> 116017000: 00000000 00000000 00000000 00000000 ................
> 116017010: 00000000 00000000 00000000 00000000 ................
> 116017020: 00000000 00000000 00000000 00000000 ................
> 116017030: 00000000 00000000 00000000 00000000 ................
> 116017040: 00000000 00000000 00000000 00000000 ................
> 116017050: 00000000 00000000 00000000 00000000 ................
> 116017060: 00000000 00000000 00000000 00000000 ................
> 116017070: 00000000 00000000 ........
> crash>
Now we're reading the same physical address as you did on
the dumpfile, and it's returning all zeroes. And the
"module 0xf8a3ea00" above shows all zeroes from a higher
location in the page because the same vmalloc translation is
done to turn it into a physical address before reading it
from the vmcore file. But instead of using the /dev/crash driver
to access the translated physical memory, the crash utility
uses the information from the ELF header's PT_LOAD segments
to find out where to find the page data in the vmcore file.
So, anyway, the "rd -p 116017000 30" command that you did
on both the live system and the dumpfile should yield the same
data.
It seems like in all examples to date, the file data read
at the greater-than-4GB PT_LOAD segment returns zeroes.
You can verify this from the crash utility's viewpoint by
doing a "help -n" during runtime when running with the dumpfile,
which will show you both the actual contents of the ELF header,
as well as the manner in which the PT_LOAD data is stored for
its use. (It's also shown with the "crash -d7 ..." output).
So again, from your original "crash.log" file, here is what the
ELF header's PT_LOAD segment contains:
Elf64_Phdr:
p_type: 1 (PT_LOAD)
p_offset: 3144876760 (bb7302d8)
p_vaddr: ffffffffffffffff
p_paddr: 100000000
p_filesz: 1073741824 (40000000)
p_memsz: 1073741824 (40000000)
p_flags: 7 (PF_X|PF_W|PF_R)
p_align: 0
And this is what the crash utility stored in its internal
data structure for that particular segment:
pt_load_segment[4]:
file_offset: bb7302d8
phys_start: 100000000
phys_end: 140000000
zero_fill: 0
And when the physical memory read request comes in, it filters
to this part of the crash utility's read_netdump() function in
netdump.c:
for (i = offset = 0; i < nd->num_pt_load_segments;
i++) {
pls = &nd->pt_load_segments[i];
if ((paddr >= pls->phys_start) &&
(paddr < pls->phys_end)) {
offset = (off_t)(paddr -
pls->phys_start) +
pls->file_offset;
break;
}
if (pls->zero_fill && (paddr >= pls->phys_end)
&&
(paddr < pls->zero_fill)) {
memset(bufptr, 0, cnt);
return cnt;
}
}
So for any physical address request between 100000000 to 140000000,
(4GB to 5GB) it will calculate the offset to seek to by subtracting
100000000 from the incoming physical address, and adding the
difference
to the starting file offset of the whole segment.
So if you wanted to, you could put debug code just prior to the
"break" above
that shows the pls->file_offset for a given incoming physical
address.
But this code has been in place forever, so it's hard to conceive
that
somehow it's not working in the case of this dumpfile. But presuming
that
it *does* go to the correct file offset location in the vmcore, and
it's
getting bogus data from there, then there's nothing that the crash
utility can do about it.
Dave
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11:08 a.m.
New subject: "cannot access vmalloc'd module memory" when loading kdump'ed vmcore in crash
Yep. My main kernel is the customized 1G userspace / 3G kernelspace, my "dump"
kernel is 3G userspace / 1G kernelspace. I originally tried using the customized kernel
for both purposes, but I get all kinds of ugly recursive task error messages once the
kernel loads part way.
-Kevin
________________________________________
From: crash-utility-bounces(a)redhat.com [crash-utility-bounces(a)redhat.com] On Behalf Of
Dave Anderson [anderson(a)redhat.com]
Sent: Thursday, October 16, 2008 6:11 AM
To: Discussion list for crash utility usage, maintenance and development
Subject: Re: [Crash-utility] "cannot access vmalloc'd module memory" when
loading kdump'ed vmcore in crash
----- "Kevin Worth" <kevin.worth(a)hp.com> wrote:
Tried version 2.0 of kexec-tools (released 7/19/2008) and still have
the same problem with zero'ed out module info. Sounds like perhaps it
is narrowed down to the 2.6.20 kernel kdump code (the most difficult
part to change out, but the part that likely gets a lot of eyes on it
and probably has the issue fixed in current versions). :\
Certainly possible. From my understanding, the kexec tools piece on
the primary kernel side is mostly concerned with creating the proper
ELF headers for the second kernel to use when /proc/vmcore is read.
And aside from the bogus p_vaddr fields that were using the hardwired
c0000000 PAGE_OFFSET based values, things looked correct.
When the user-space code on the secondary kernel reads the /proc/vmcore
pseudo-file, the secondary kdump kernel dynamically kmaps and reads the
physical memory from the "oldmem" location, and copies it out to user-space.
Why it would read zeroed-out memory from those locations is hard to understand.
I was looking at the "fs/proc/vmcore.c" sources yesterday in our RHEL5
kernel (2.6.18 + patches) for something that could be a issue with the
1GB/3GB split, and also given that your secondary kdump kernel is
still a 3GB/1GB kernel (is that right?). But I couldn't see anything
there.
Dave
-Kevin
-----Original Message-----
From: crash-utility-bounces(a)redhat.com
[mailto:crash-utility-bounces@redhat.com] On Behalf Of Worth, Kevin
Sent: Wednesday, October 15, 2008 2:43 PM
To: Discussion list for crash utility usage, maintenance and
development
Subject: RE: [Crash-utility] "cannot access vmalloc'd module memory"
when loading kdump'ed vmcore in crash
Sorry please ignore the second paragraph... I am already running the
most recent version in Ubuntu, 20070330 from Simon Horman's
kexec-tools-testing and kernel 2.6.20. ... may try a newer version of
kexec-tools-testing to see if anything changes.
-Kevin
-----Original Message-----
From: Worth, Kevin
Sent: Wednesday, October 15, 2008 2:31 PM
To: Discussion list for crash utility usage, maintenance and
development
Subject: RE: [Crash-utility] "cannot access vmalloc'd module memory"
when loading kdump'ed vmcore in crash
So Dave, at this am I correct in the assumption that it sounds like
this is not a problem with crash, but with the dump file itself? I
tried one more go at modifying the kexec-tools to have the correct
PAGE_OFFSET defined and still got the same type of results (all zeroes
at the module's address), so that doesn't seem to be it.
Maybe this is a better question to take to the kexec mailing list, but
do you know where the line is drawn between the kernel support or the
userspace (kexec-tools)? I'm presuming that the kernel support is tied
to each kernel (i.e. since I'm on 2.6.20 this issue could have been
resolved in a more recent kernel). I'm wondering if I can pull a newer
kexec-tools and that they might work with 2.6.20 and possibly have
this issue resolved.
-Kevin
-----Original Message-----
From: crash-utility-bounces(a)redhat.com
[mailto:crash-utility-bounces@redhat.com] On Behalf Of Dave Anderson
Sent: Wednesday, October 15, 2008 6:53 AM
To: Discussion list for crash utility usage, maintenance and
development
Subject: Re: [Crash-utility] "cannot access vmalloc'd module memory"
when loading kdump'ed vmcore in crash
----- "Kevin Worth" <kevin.worth(a)hp.com> wrote:
> Hi Dave,
>
> Before you responded I noticed that a simple "make modules" didn't
> work because my kernel wasn't exporting the symbol. Rather than do
> anything risky/complex which might risk mucking up the
troubleshooting
> process, I just rebuilt the kernel. It built just fine and now I
can
> load crash and I see "DUMPFILE: /dev/crash" when I load up crash.
Let
> me try walking through the steps that you had me do previously,
this
> time using /dev/crash instead of /dev/mem and /dev/kmem
You made one small error (but not totally fatal) in the suggested
steps.
See my comments below...
>
> >From my limited understanding of what's going on here, it would
> appear that the dump file is missing some data, or else crash is
> looking in the wrong place for it.
The crash utility is a slave to what is indicated in the PT_LOAD
segments of the ELF header of the kdump vmcore. In the case of
the physical memory chunk that starts at 4GB physical on your
machine,
this is what's in the ELF header (from your original "crash.log"
file):
Elf64_Phdr:
p_type: 1 (PT_LOAD)
p_offset: 3144876760 (bb7302d8)
p_vaddr: ffffffffffffffff
p_paddr: 100000000
p_filesz: 1073741824 (40000000)
p_memsz: 1073741824 (40000000)
p_flags: 7 (PF_X|PF_W|PF_R)
p_align: 0
What that says is: for the range of physical memory starting
at 0x100000000 (p_paddr), the vmcore contains a block of
memory starting at file offset (p_offset) 3144876760/0xbb7302d8
that is 1073741824/0x40000000 (p_filesz) bytes long.
More simply put, the 1GB of physical memory from 4GB to 5GB
can be found in the vmcore file starting at file offset 3144876760.
So if a request for physical memory page 0x100000000 comes
in, the crash utility reads from vmcore file offset 3144876760.
If the next physical page were requested, i.e., at 0x100001000,
it would read from vmcore file offset 3144876760+4096. It's
as simple as that -- so when you suggest that "crash is looking
in the wrong place for it", well, there's nothing that the
crash utility can do differently.
Now, back to the test sequence:
> ---Live system---
>
> KERNEL: vmlinux-devcrash
> DUMPFILE: /dev/crash
> CPUS: 2
> DATE: Tue Oct 14 16:08:28 2008
> UPTIME: 00:02:07
> LOAD AVERAGE: 0.17, 0.08, 0.03
> TASKS: 97
> NODENAME: test-machine
> RELEASE: 2.6.20-17.39-custom2
> VERSION: #1 SMP Tue Oct 14 13:45:17 PDT 2008
> MACHINE: i686 (2200 Mhz)
> MEMORY: 5 GB
> PID: 5628
> COMMAND: "crash"
> TASK: 5d4c2560 [THREAD_INFO: f3de6000]
> CPU: 1
> STATE: TASK_RUNNING (ACTIVE)
>
> crash> p modules
> modules = $2 = {
> next = 0xf8a3ea04,
> prev = 0xf8842104
> }
>
> crash> module 0xf8a3ea00
> struct module {
> state = MODULE_STATE_LIVE,
> list = {
> next = 0xf8d10484,
> prev = 0x403c63a4
> },
> name =
>
"crash\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\
>
000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\
>
000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000",
> mkobj = {
> kobj = {
> k_name = 0xf8a3ea4c "crash",
> name =
> "crash\000\000\000\000\000\000\000\000\000\000\000\000\000\000",
> kref = {
> refcount = {
> counter = 3
> }
> },
> entry = {
> next = 0x403c6068,
> prev = 0xf8d104e4
> },
> parent = 0x403c6074
> ...
>
> crash> vtop 0xf8a3ea00
> VIRTUAL PHYSICAL
> f8a3ea00 116017a00
OK -- so the physical memory location of the module data structure
is at physical address 116017a00, but...
>
> PAGE DIRECTORY: 4044b000
> PGD: 4044b018 => 6001
> PMD: 6e28 => 1d51a067
> PTE: 1d51a1f0 => 116017163
> PAGE: 116017000
>
> PTE PHYSICAL FLAGS
> 116017163 116017000 (PRESENT|RW|ACCESSED|DIRTY|GLOBAL)
>
> PAGE PHYSICAL MAPPING INDEX CNT FLAGS
> 472c02e0 116017000 0 229173 1 80000000
>
You're reading from the beginning of the page, i.e., 116017000
instead of where the module structure is at 116017a00:
> crash> rd -p 116017000 30
> 116017000: 53e58955 d089c389 4d8bca89 74c98508 U..S.......M...t
> 116017010: 01e9831f b85b0d74 ffffffea ffffba5d ....t.[.....]...
> 116017020: 03c3ffff 53132043 26b48d24 00000000 ....C .S$..&....
> 116017030: 89204389 5d5b2453 26b48dc3 00000000 .C .S$[]...&....
> 116017040: 83e58955 55892cec 08558be4 89f45d89 U....,.U..U..]..
> 116017050: 7d89f875 ffeabffc 4d89ffff 8b028be0 u..}.......M....
> 116017060: c3890452 ac0fd689 45890cf3 0ceec1ec R..........E....
> 116017070: 5589c889 89d231f0 ...U.1..
> crash>
>
So therefore you're not seeing the "crash" strings embedded in
the raw physical data. Now, although it would have been "nice"
if you could have shown the contents of the module structure via
the physical address, the fact remains that since you used the
/dev/crash driver, the "module 0xf8a3ea00" command required that
the crash utility first translate the vmalloc address into its
physical equivalent, and then read from there.
In any case, you do have a dump of physical memory from 116017000
which at least is in the same 4k page as the module data structure,
so it should not change when read from the dumpfile.
> ---Using dump file---
>
>
> please wait... (gathering module symbol data)
> WARNING: cannot access vmalloc'd module memory
>
> KERNEL: vmlinux-devcrash
> DUMPFILE: /var/crash/vmcore
> CPUS: 2
> DATE: Tue Oct 14 16:09:32 2008
> UPTIME: 00:03:12
> LOAD AVERAGE: 0.09, 0.08, 0.02
> TASKS: 97
> NODENAME: test-machine
> RELEASE: 2.6.20-17.39-custom2
> VERSION: #1 SMP Tue Oct 14 13:45:17 PDT 2008
> MACHINE: i686 (2200 Mhz)
> MEMORY: 5 GB
> PANIC: "[ 192.148000] SysRq : Trigger a crashdump"
> PID: 0
> COMMAND: "swapper"
> TASK: 403c0440 (1 of 2) [THREAD_INFO: 403f2000]
> CPU: 0
> STATE: TASK_RUNNING (SYSRQ)
>
> crash> p modules
> modules = $2 = {
> next = 0xf8a3ea04,
> prev = 0xf8842104
> }
>
> crash> module 0xf8a3ea00
> struct module {
> state = MODULE_STATE_LIVE,
> list = {
> next = 0x0,
> prev = 0x0
> },
> name =
>
"\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\0
>
00\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\0
>
00\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\0
> 00\000",
> mkobj = {
> kobj = {
> k_name = 0x0,
> name =
> "\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\0
> 00\000\000",
> kref = {
> refcount = {
> counter = 0
> }
> },
> entry = {
> next = 0x0,
> prev = 0x0
> ...
>
> crash> vtop 0xf8a3ea00
> VIRTUAL PHYSICAL
> f8a3ea00 116017a00
>
> PAGE DIRECTORY: 4044b000
> PGD: 4044b018 => 6001
> PMD: 6e28 => 1d51a067
> PTE: 1d51a1f0 => 116017163
> PAGE: 116017000
>
> PTE PHYSICAL FLAGS
> 116017163 116017000 (PRESENT|RW|ACCESSED|DIRTY|GLOBAL)
>
> PAGE PHYSICAL MAPPING INDEX CNT FLAGS
> 472c02e0 116017000 0 229173 1 80000000
>
> crash> rd -p 116017000 30
> 116017000: 00000000 00000000 00000000 00000000 ................
> 116017010: 00000000 00000000 00000000 00000000 ................
> 116017020: 00000000 00000000 00000000 00000000 ................
> 116017030: 00000000 00000000 00000000 00000000 ................
> 116017040: 00000000 00000000 00000000 00000000 ................
> 116017050: 00000000 00000000 00000000 00000000 ................
> 116017060: 00000000 00000000 00000000 00000000 ................
> 116017070: 00000000 00000000 ........
> crash>
Now we're reading the same physical address as you did on
the dumpfile, and it's returning all zeroes. And the
"module 0xf8a3ea00" above shows all zeroes from a higher
location in the page because the same vmalloc translation is
done to turn it into a physical address before reading it
from the vmcore file. But instead of using the /dev/crash driver
to access the translated physical memory, the crash utility
uses the information from the ELF header's PT_LOAD segments
to find out where to find the page data in the vmcore file.
So, anyway, the "rd -p 116017000 30" command that you did
on both the live system and the dumpfile should yield the same
data.
It seems like in all examples to date, the file data read
at the greater-than-4GB PT_LOAD segment returns zeroes.
You can verify this from the crash utility's viewpoint by
doing a "help -n" during runtime when running with the dumpfile,
which will show you both the actual contents of the ELF header,
as well as the manner in which the PT_LOAD data is stored for
its use. (It's also shown with the "crash -d7 ..." output).
So again, from your original "crash.log" file, here is what the
ELF header's PT_LOAD segment contains:
Elf64_Phdr:
p_type: 1 (PT_LOAD)
p_offset: 3144876760 (bb7302d8)
p_vaddr: ffffffffffffffff
p_paddr: 100000000
p_filesz: 1073741824 (40000000)
p_memsz: 1073741824 (40000000)
p_flags: 7 (PF_X|PF_W|PF_R)
p_align: 0
And this is what the crash utility stored in its internal
data structure for that particular segment:
pt_load_segment[4]:
file_offset: bb7302d8
phys_start: 100000000
phys_end: 140000000
zero_fill: 0
And when the physical memory read request comes in, it filters
to this part of the crash utility's read_netdump() function in
netdump.c:
for (i = offset = 0; i < nd->num_pt_load_segments;
i++) {
pls = &nd->pt_load_segments[i];
if ((paddr >= pls->phys_start) &&
(paddr < pls->phys_end)) {
offset = (off_t)(paddr -
pls->phys_start) +
pls->file_offset;
break;
}
if (pls->zero_fill && (paddr >= pls->phys_end)
&&
(paddr < pls->zero_fill)) {
memset(bufptr, 0, cnt);
return cnt;
}
}
So for any physical address request between 100000000 to 140000000,
(4GB to 5GB) it will calculate the offset to seek to by subtracting
100000000 from the incoming physical address, and adding the
difference
to the starting file offset of the whole segment.
So if you wanted to, you could put debug code just prior to the
"break" above
that shows the pls->file_offset for a given incoming physical
address.
But this code has been in place forever, so it's hard to conceive
that
somehow it's not working in the case of this dumpfile. But presuming
that
it *does* go to the correct file offset location in the vmcore, and
it's
getting bogus data from there, then there's nothing that the crash
utility can do about it.
Dave
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4:02 p.m.
New subject: "cannot access vmalloc'd module memory" when loading kdump'ed vmcore in crash
Hi Dave,
Thanks for all your help with the crash/kexec troubleshooting, I really appreciate it. At
this point I’m going toward the kernel/kexec/kdump side of things and am trying to do
whatever research I can before sending another mail to kexec-ml. I tried to see if the
issue still occurs with the Ubuntu “generic” kernel, which has HIGHMEM4G instead of
HIGHMEM64G, and the standard VMSPLIT/PAGE_OFFSET setting. I also noted that enabling
HIGHMEM64G also implicitly seems to select CONFIG_RESOURCES_64BIT=y which was marked
Experimental in 2.6.20 (hmmm).
Interestingly enough, when I use the Ubuntu "generic" kernel (HIGHMEM4G + normal
VMSPLIT), the crash dump works just fine and I can view the modules, etc. This leads me to
believe that it's either the HIGHMEM64G or the modified VMSPLIT that is causing the
problem (or both in combination). I'm going to try compiling kernels with only one
setting changed in each to try to isolate the issue.
Warning: probably a stupid question-- My machine has 4GB of memory. If I boot the
"generic" kernel with HIGHMEM4G, only 3GB is recognized (according to my
understanding of free and /proc/meminfo results). However, when I create a dump and load
it up in crash, I see " MEMORY: 4 GB". Am I just misunderstanding the output of
free/meminfo or is this just crash calculating something differently? The reason I ask is
that if it turns out that HIGHMEM64G is causing the problem with putting the
vmalloc'ed memory into the dump file, then I am trying to understand if that becomes a
compromise of the system only being able to use 3GB of RAM but crash dumps still work.
-Kevin
9:12 p.m.
New subject: "cannot access vmalloc'd module memory" when loading kdump'ed vmcore in crash
Thought that perhaps the newest kexec-toools from git would help, with changelog entries
like "Parse contents of /proc/iomem instead of hardcoding RAM ranges." No joy.
:\
Dave, one last question for you before I attempt to get assistance from kexec folks... I
just noticed that crash reports my memory is 5GB. I have 4GB of physical memory. Am I
correct in assuming this is just some cosmetic detail?
-Kevin
-----Original Message-----
From: Worth, Kevin
Sent: Wednesday, October 15, 2008 4:16 PM
To: Discussion list for crash utility usage, maintenance and development
Subject: RE: [Crash-utility] "cannot access vmalloc'd module memory" when
loading kdump'ed vmcore in crash
Tried version 2.0 of kexec-tools (released 7/19/2008) and still have the same problem with
zero'ed out module info. Sounds like perhaps it is narrowed down to the 2.6.20 kernel
kdump code (the most difficult part to change out, but the part that likely gets a lot of
eyes on it and probably has the issue fixed in current versions). :\
-Kevin
-----Original Message-----
From: crash-utility-bounces(a)redhat.com [mailto:crash-utility-bounces@redhat.com] On Behalf
Of Worth, Kevin
Sent: Wednesday, October 15, 2008 2:43 PM
To: Discussion list for crash utility usage, maintenance and development
Subject: RE: [Crash-utility] "cannot access vmalloc'd module memory" when
loading kdump'ed vmcore in crash
Sorry please ignore the second paragraph... I am already running the most recent version
in Ubuntu, 20070330 from Simon Horman's kexec-tools-testing and kernel 2.6.20. ... may
try a newer version of kexec-tools-testing to see if anything changes.
-Kevin
-----Original Message-----
From: Worth, Kevin
Sent: Wednesday, October 15, 2008 2:31 PM
To: Discussion list for crash utility usage, maintenance and development
Subject: RE: [Crash-utility] "cannot access vmalloc'd module memory" when
loading kdump'ed vmcore in crash
So Dave, at this am I correct in the assumption that it sounds like this is not a problem
with crash, but with the dump file itself? I tried one more go at modifying the
kexec-tools to have the correct PAGE_OFFSET defined and still got the same type of results
(all zeroes at the module's address), so that doesn't seem to be it.
Maybe this is a better question to take to the kexec mailing list, but do you know where
the line is drawn between the kernel support or the userspace (kexec-tools)? I'm
presuming that the kernel support is tied to each kernel (i.e. since I'm on 2.6.20
this issue could have been resolved in a more recent kernel). I'm wondering if I can
pull a newer kexec-tools and that they might work with 2.6.20 and possibly have this issue
resolved.
-Kevin
-----Original Message-----
From: crash-utility-bounces(a)redhat.com [mailto:crash-utility-bounces@redhat.com] On Behalf
Of Dave Anderson
Sent: Wednesday, October 15, 2008 6:53 AM
To: Discussion list for crash utility usage, maintenance and development
Subject: Re: [Crash-utility] "cannot access vmalloc'd module memory" when
loading kdump'ed vmcore in crash
----- "Kevin Worth" <kevin.worth(a)hp.com> wrote:
Hi Dave,
Before you responded I noticed that a simple "make modules" didn't
work because my kernel wasn't exporting the symbol. Rather than do
anything risky/complex which might risk mucking up the troubleshooting
process, I just rebuilt the kernel. It built just fine and now I can
load crash and I see "DUMPFILE: /dev/crash" when I load up crash. Let
me try walking through the steps that you had me do previously, this
time using /dev/crash instead of /dev/mem and /dev/kmem
You made one small error (but not totally fatal) in the suggested steps.
See my comments below...
>From my limited understanding of what's going on here, it would
appear that the dump file is missing some data, or else crash is
looking in the wrong place for it.
The crash utility is a slave to what is indicated in the PT_LOAD
segments of the ELF header of the kdump vmcore. In the case of
the physical memory chunk that starts at 4GB physical on your machine,
this is what's in the ELF header (from your original "crash.log" file):
Elf64_Phdr:
p_type: 1 (PT_LOAD)
p_offset: 3144876760 (bb7302d8)
p_vaddr: ffffffffffffffff
p_paddr: 100000000
p_filesz: 1073741824 (40000000)
p_memsz: 1073741824 (40000000)
p_flags: 7 (PF_X|PF_W|PF_R)
p_align: 0
What that says is: for the range of physical memory starting
at 0x100000000 (p_paddr), the vmcore contains a block of
memory starting at file offset (p_offset) 3144876760/0xbb7302d8
that is 1073741824/0x40000000 (p_filesz) bytes long.
More simply put, the 1GB of physical memory from 4GB to 5GB
can be found in the vmcore file starting at file offset 3144876760.
So if a request for physical memory page 0x100000000 comes
in, the crash utility reads from vmcore file offset 3144876760.
If the next physical page were requested, i.e., at 0x100001000,
it would read from vmcore file offset 3144876760+4096. It's
as simple as that -- so when you suggest that "crash is looking
in the wrong place for it", well, there's nothing that the
crash utility can do differently.
Now, back to the test sequence:
---Live system---
KERNEL: vmlinux-devcrash
DUMPFILE: /dev/crash
CPUS: 2
DATE: Tue Oct 14 16:08:28 2008
UPTIME: 00:02:07
LOAD AVERAGE: 0.17, 0.08, 0.03
TASKS: 97
NODENAME: test-machine
RELEASE: 2.6.20-17.39-custom2
VERSION: #1 SMP Tue Oct 14 13:45:17 PDT 2008
MACHINE: i686 (2200 Mhz)
MEMORY: 5 GB
PID: 5628
COMMAND: "crash"
TASK: 5d4c2560 [THREAD_INFO: f3de6000]
CPU: 1
STATE: TASK_RUNNING (ACTIVE)
crash> p modules
modules = $2 = {
next = 0xf8a3ea04,
prev = 0xf8842104
}
crash> module 0xf8a3ea00
struct module {
state = MODULE_STATE_LIVE,
list = {
next = 0xf8d10484,
prev = 0x403c63a4
},
name =
"crash\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\
000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\
000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000",
mkobj = {
kobj = {
k_name = 0xf8a3ea4c "crash",
name =
"crash\000\000\000\000\000\000\000\000\000\000\000\000\000\000",
kref = {
refcount = {
counter = 3
}
},
entry = {
next = 0x403c6068,
prev = 0xf8d104e4
},
parent = 0x403c6074
...
crash> vtop 0xf8a3ea00
VIRTUAL PHYSICAL
f8a3ea00 116017a00
OK -- so the physical memory location of the module data structure
is at physical address 116017a00, but...
PAGE DIRECTORY: 4044b000
PGD: 4044b018 => 6001
PMD: 6e28 => 1d51a067
PTE: 1d51a1f0 => 116017163
PAGE: 116017000
PTE PHYSICAL FLAGS
116017163 116017000 (PRESENT|RW|ACCESSED|DIRTY|GLOBAL)
PAGE PHYSICAL MAPPING INDEX CNT FLAGS
472c02e0 116017000 0 229173 1 80000000
You're reading from the beginning of the page, i.e., 116017000
instead of where the module structure is at 116017a00:
crash> rd -p 116017000 30
116017000: 53e58955 d089c389 4d8bca89 74c98508 U..S.......M...t
116017010: 01e9831f b85b0d74 ffffffea ffffba5d ....t.[.....]...
116017020: 03c3ffff 53132043 26b48d24 00000000 ....C .S$..&....
116017030: 89204389 5d5b2453 26b48dc3 00000000 .C .S$[]...&....
116017040: 83e58955 55892cec 08558be4 89f45d89 U....,.U..U..]..
116017050: 7d89f875 ffeabffc 4d89ffff 8b028be0 u..}.......M....
116017060: c3890452 ac0fd689 45890cf3 0ceec1ec R..........E....
116017070: 5589c889 89d231f0 ...U.1..
crash>
So therefore you're not seeing the "crash" strings embedded in
the raw physical data. Now, although it would have been "nice"
if you could have shown the contents of the module structure via
the physical address, the fact remains that since you used the
/dev/crash driver, the "module 0xf8a3ea00" command required that
the crash utility first translate the vmalloc address into its
physical equivalent, and then read from there.
In any case, you do have a dump of physical memory from 116017000
which at least is in the same 4k page as the module data structure,
so it should not change when read from the dumpfile.
> ---Using dump file---
>
>
> please wait... (gathering module symbol data)
> WARNING: cannot access vmalloc'd module memory
>
> KERNEL: vmlinux-devcrash
> DUMPFILE: /var/crash/vmcore
> CPUS: 2
> DATE: Tue Oct 14 16:09:32 2008
> UPTIME: 00:03:12
> LOAD AVERAGE: 0.09, 0.08, 0.02
> TASKS: 97
> NODENAME: test-machine
> RELEASE: 2.6.20-17.39-custom2
> VERSION: #1 SMP Tue Oct 14 13:45:17 PDT 2008
> MACHINE: i686 (2200 Mhz)
> MEMORY: 5 GB
> PANIC: "[ 192.148000] SysRq : Trigger a crashdump"
> PID: 0
> COMMAND: "swapper"
> TASK: 403c0440 (1 of 2) [THREAD_INFO: 403f2000]
> CPU: 0
> STATE: TASK_RUNNING (SYSRQ)
>
> crash> p modules
> modules = $2 = {
> next = 0xf8a3ea04,
> prev = 0xf8842104
> }
>
> crash> module 0xf8a3ea00
> struct module {
> state = MODULE_STATE_LIVE,
> list = {
> next = 0x0,
> prev = 0x0
> },
> name =
> "\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\0
> 00\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\0
> 00\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\0
> 00\000",
> mkobj = {
> kobj = {
> k_name = 0x0,
> name =
> "\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\000\0
> 00\000\000",
> kref = {
> refcount = {
> counter = 0
> }
> },
> entry = {
> next = 0x0,
> prev = 0x0
> ...
>
> crash> vtop 0xf8a3ea00
> VIRTUAL PHYSICAL
> f8a3ea00 116017a00
PAGE DIRECTORY: 4044b000
PGD: 4044b018 => 6001
PMD: 6e28 => 1d51a067
PTE: 1d51a1f0 => 116017163
PAGE: 116017000
PTE PHYSICAL FLAGS
116017163 116017000 (PRESENT|RW|ACCESSED|DIRTY|GLOBAL)
PAGE PHYSICAL MAPPING INDEX CNT FLAGS
472c02e0 116017000 0 229173 1 80000000
> crash> rd -p 116017000 30
> 116017000: 00000000 00000000 00000000 00000000 ................
> 116017010: 00000000 00000000 00000000 00000000 ................
> 116017020: 00000000 00000000 00000000 00000000 ................
> 116017030: 00000000 00000000 00000000 00000000 ................
> 116017040: 00000000 00000000 00000000 00000000 ................
> 116017050: 00000000 00000000 00000000 00000000 ................
> 116017060: 00000000 00000000 00000000 00000000 ................
> 116017070: 00000000 00000000 ........
> crash>
Now we're reading the same physical address as you did on
the dumpfile, and it's returning all zeroes. And the
"module 0xf8a3ea00" above shows all zeroes from a higher
location in the page because the same vmalloc translation is
done to turn it into a physical address before reading it
from the vmcore file. But instead of using the /dev/crash driver
to access the translated physical memory, the crash utility
uses the information from the ELF header's PT_LOAD segments
to find out where to find the page data in the vmcore file.
So, anyway, the "rd -p 116017000 30" command that you did
on both the live system and the dumpfile should yield the same
data.
It seems like in all examples to date, the file data read
at the greater-than-4GB PT_LOAD segment returns zeroes.
You can verify this from the crash utility's viewpoint by
doing a "help -n" during runtime when running with the dumpfile,
which will show you both the actual contents of the ELF header,
as well as the manner in which the PT_LOAD data is stored for
its use. (It's also shown with the "crash -d7 ..." output).
So again, from your original "crash.log" file, here is what the
ELF header's PT_LOAD segment contains:
Elf64_Phdr:
p_type: 1 (PT_LOAD)
p_offset: 3144876760 (bb7302d8)
p_vaddr: ffffffffffffffff
p_paddr: 100000000
p_filesz: 1073741824 (40000000)
p_memsz: 1073741824 (40000000)
p_flags: 7 (PF_X|PF_W|PF_R)
p_align: 0
And this is what the crash utility stored in its internal
data structure for that particular segment:
pt_load_segment[4]:
file_offset: bb7302d8
phys_start: 100000000
phys_end: 140000000
zero_fill: 0
And when the physical memory read request comes in, it filters
to this part of the crash utility's read_netdump() function in
netdump.c:
for (i = offset = 0; i < nd->num_pt_load_segments; i++) {
pls = &nd->pt_load_segments[i];
if ((paddr >= pls->phys_start) &&
(paddr < pls->phys_end)) {
offset = (off_t)(paddr - pls->phys_start) +
pls->file_offset;
break;
}
if (pls->zero_fill && (paddr >= pls->phys_end)
&&
(paddr < pls->zero_fill)) {
memset(bufptr, 0, cnt);
return cnt;
}
}
So for any physical address request between 100000000 to 140000000,
(4GB to 5GB) it will calculate the offset to seek to by subtracting
100000000 from the incoming physical address, and adding the difference
to the starting file offset of the whole segment.
So if you wanted to, you could put debug code just prior to the "break" above
that shows the pls->file_offset for a given incoming physical address.
But this code has been in place forever, so it's hard to conceive that
somehow it's not working in the case of this dumpfile. But presuming that
it *does* go to the correct file offset location in the vmcore, and it's
getting bogus data from there, then there's nothing that the crash
utility can do about it.
Dave
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7 comments
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participants (2)
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Dave Anderson -
Worth, Kevin