Ankita Garg wrote:
Hi,
Am working on backporting relocatable kernel support for x86_64 from
2.6.22.1 kernel to 2.6.21.4. kdump is working fine. But when opening the
vmcore file with crash, I get the following error:
I had a discussion with Ankita about this problem. This is what i
think is happening.
This x86-64 kernel has CONFIG_NUMA off with SPARSEMEM support.
The failure occurs as line 11738 in memory.c [ This is with
latest crash ]
crash: invalid structure member offset: pglist_data_node_mem_map
FILE: memory.c LINE: 11738 FUNCTION: dump_memory_nodes()
Looking at the crash source here is the code in question :
11728 if (IS_SPARSEMEM()) {
11729 zone_mem_map = 0;
11730 zone_start_mapnr = 0;
11731 if (zone_size) {
11732 phys = PTOB(zone_start_pfn);
11733 zone_start_mapnr =
phys/PAGESIZE();
11734 }
11735
11736 } else if (!(vt->flags & NODES) &&
11737 INVALID_MEMBER(zone_zone_mem_map)) {
11738
readmem(pgdat+OFFSET(pglist_data_node_mem_map),
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
11739 KVADDR, &zone_mem_map,
sizeof(void *),
11740 "contig_page_data
mem_map",FAULT_ON_ERROR);
11741 if (zone_size)
11742 zone_mem_map += cum_zone_size *
SIZE(page);
The code is trying to read pglist_data_node_mem_map value which does
not exist.
[Since CONFIG_NUMA is off]. It should have entered the if
(IS_SPARSEMEM())
condition [ line 11728 ] since SPARSEMEM is enabled for this kernel.
The flag value of SPARSEMEM is set by this code in memory.c
558 if (kernel_symbol_exists("mem_map")) {
559 get_symbol_data("mem_map", sizeof(char *),
&vt->mem_map);
560 vt->flags |= FLATMEM;
561 } else if (kernel_symbol_exists("mem_section"))
562 vt->flags |= SPARSEMEM;
563 else
564 vt->flags |= DISCONTIGMEM;
But what i found was SPARSEMEM flag is not set, instead FLATMEM is set as
mem_map symbol exist in this particular kernel.[ mem_section kernel
symbol
is also present in this kernel]
[crash-4.0-4.8]# cat /boot/System.map | grep mem_map
ffffffff8072dab0 B mem_map
[crash-4.0-4.8]# cat /boot/System.map | grep mem_section
ffffffff8072e800 B mem_section
From kernel source mm/memory.c: mem_map is defined if
CONFIG_NEED_MULTIPLE_NODES
is not defined. Which is the case here.
I am not a mm expert so i can't tell what to make out of this
situation where
both mem_map and mem_section kernel symbol exist. Anyone ??
Anyway as for the crash problem this could be fixed by rearranging the
above code as follows:
- if (kernel_symbol_exists("mem_map")) {
+ if (kernel_symbol_exists("mem_section"))
+ vt->flags |= SPARSEMEM;
+ else if (kernel_symbol_exists("mem_map")) {
get_symbol_data("mem_map", sizeof(char *), &vt->mem_map);
vt->flags |= FLATMEM;
- } else if (kernel_symbol_exists("mem_section"))
- vt->flags |= SPARSEMEM;
- else
+ } else
But since i am not very sure about the mm code, there might be a
better way to
fix this.
Thanks
-Sachin
