Our QA group recently ran into a makedumpfile problem while testing kdump/makedumpfile w/upstream 3.7.1 kernels, which had to do with the filtering of pages on a 12GB ppc64 system. The problem can be seen using -d31 on the "vmcore.full" ELF dumpfile: # makedumpfile -c -d31 -x vmlinux vmcore.full vmcore.out The kernel version is not supported. The created dumpfile may be incomplete. Excluding free pages : [ 0 %] page_to_pfn: Can't convert the address of page descriptor (c0000002ef031c00) to pfn. page_to_pfn: Can't convert the address of page descriptor (c0000002ef031c00) to pfn. makedumpfile Failed. # Other -d flag values yield different results, for example, where a dumpfile does get created when filtering "user pages" with -d8: # makedumpfile -c -d8 -x vmlinux vmcore.full vmcore.out The kernel version is not supported. The created dumpfile may be incomplete. Copying data : [100 %] The dumpfile is saved to vmcore.out. makedumpfile Completed. # But the resultant vmcore.out could not be analyzed with crash: # crash vmlinux vmcore.out crash 6.1.1-1.el7 Copyright (C) 2002-2012 Red Hat, Inc. Copyright (C) 2004, 2005, 2006, 2010 IBM Corporation Copyright (C) 1999-2006 Hewlett-Packard Co Copyright (C) 2005, 2006, 2011, 2012 Fujitsu Limited Copyright (C) 2006, 2007 VA Linux Systems Japan K.K. Copyright (C) 2005, 2011 NEC Corporation Copyright (C) 1999, 2002, 2007 Silicon Graphics, Inc. Copyright (C) 1999, 2000, 2001, 2002 Mission Critical Linux, Inc. This program is free software, covered by the GNU General Public License, and you are welcome to change it and/or distribute copies of it under certain conditions. Enter "help copying" to see the conditions. This program has absolutely no warranty. Enter "help warranty" for details. GNU gdb (GDB) 7.3.1 Copyright (C) 2011 Free Software Foundation, Inc. License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html> This is free software: you are free to change and redistribute it. There is NO WARRANTY, to the extent permitted by law. Type "show copying" and "show warranty" for details. This GDB was configured as "powerpc64-unknown-linux-gnu"... crash: page excluded: kernel virtual address: c00000000075edb0 type: "cpu_possible_mask" # Clearly the kernel page containing the "cpu_possible_mask" should never be determined to be a user page. So after debugging this, I first noted that makedumpfile did in fact determine that the 64K physical page at 0x750000 was a user page because its associated page.mapping field had the PAGE_MAPPING_ANON bit set. But further debugging showed that __exclude_unnecessary_pages() was being passed invalid mem_map array addresses, and as a result the page contents being tested were bogus. And the reason for the invalid mem_map addresses is because is_sparsemem_extreme() is incorrectly returning FALSE: int is_sparsemem_extreme(void) { if (ARRAY_LENGTH(mem_section) == (NR_MEM_SECTIONS() / _SECTIONS_PER_ROOT_EXTREME())) return TRUE; else return FALSE; } on a kernel which most definitely is CONFIG_SPARSEMEM_EXTREME. The kernel's declaration of mem_section is this: #ifdef CONFIG_SPARSEMEM_EXTREME struct mem_section *mem_section[NR_SECTION_ROOTS] ____cacheline_internodealigned_in_smp; #else struct mem_section mem_section[NR_SECTION_ROOTS][SECTIONS_PER_ROOT] ____cacheline_internodealigned_in_smp; #endif EXPORT_SYMBOL(mem_section); And this ppc64 kernel's mem_section is this: crash> whatis mem_section struct mem_section *mem_section[2048]; crash> The is_sparsemem_extreme() function is similar to that of the crash utility's, which was modified in 2008 like so: - - if (get_array_length("mem_section", NULL, 0) == - (NR_MEM_SECTIONS() / _SECTIONS_PER_ROOT_EXTREME())) + + if ((get_array_length("mem_section", &dimension, 0) == + (NR_MEM_SECTIONS() / _SECTIONS_PER_ROOT_EXTREME())) || !dimension) vt->flags |= SPARSEMEM_EX; The patch above simplifies things by also checking whether it's a two-dimensional array. It was actually put in place in crash-4.0-7.2 for s390/s390x CONFIG_SPARSEMEM support: - Implement support for s390/s390x CONFIG_SPARSEMEM kernels. Without the patch, crash sessions would fail during initialization with the error message: "crash: CONFIG_SPARSEMEM kernels not supported for this architecture". (holzheu at linux.vnet.ibm.com) In any case, if I hack makedumpfile so that is_sparsemem_extreme() returns TRUE, everything works fine. I haven't checked why the original math fails in the case of the ppc64 kernel, while it does not fail in a CONFIG_SPARSEMEM_EXTREME x86_64 kernel, for example. (page size maybe?) But obviously the simpler dimemsion-check is a better way to do it. Of course, within the current constraints of makedumpfile, it's not that easy. Ideally the kernel could pass the configuration in the vmcoreinfo with a VMCOREINFO_CONFIG(name). But anyway, I'll leave that up to you. Thanks, Dave
