Sachin P. Sant wrote: > 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 The crash patch above looks fine to me -- I'll give it a test run.