Hi All, Please find a set of patches that introduce a 'slimdump' framework. Details as described below. Problem -------- A system configured with kdump, captures the kernel memory for all types of crashes even when it doesn't make much sense to do so. For instance, system crashes triggered due to hardware errors don't need a complete dump of the memory for investigation. In the case of crashes triggered by fatal machine check exceptions (MCE) due to unrecoverable memory errors, it is even dangerous to read the crashing kernel's memory. When the kexec kernel reads the crashing kernel's memory, it 'consumes' the data from the faulty memory location, potentially causing a recursion of faults. This problem was previously discussed in the kernel community, with a proposal to leave out kernel memory regions from /proc/vmcore (refer: mail threads pertaining to http://article.gmane.org/gmane.linux.kernel/1148266). However there were suggestions against making this behaviour a kernel policy. Solution --------- Since capturing of crashing kernel's memory for hardware error induced crashes isn't required or is dangerous, we introduce a mechanism to generate 'slimdump'. Basically, a new elf-note of type NT_NOCOREDUMP type is added by the kernel to the vmcore, which is recognised by all tools in the kdump chain to generate and save a 'slimdump' that contains only elf-headers and the elf-note section. The elf-note section may be used to add description about the cause of the error. The enclosed set of patches make changes to kernel, kexec, makedumpfile and crash tool to make them recognise the NT_NOCOREDUMP elf-note and generate a 'slimdump'. Also, fatal MCEs in the kernel is turned into a consumer of the slimdump mechanism to prevent collection of normal kdump. Alternatively, the user has an option (through suitable makedumpfile or kdump configuration options) to collect the complete vmcore or to extract the 'dmesg' from /proc/vmcore. Screen logs ------------- # mce-inject ~/mce/mce-test/cases/soft-inj/panic_ucr/data/srar_over [ 4934.748416] [Hardware Error]: CPU 0: Machine Check Exception: 6 Bank 2: f580000000000000 [ 4934.749079] [Hardware Error]: RIP 73:<000000001eadbabe> [ 4934.749079] [Hardware Error]: TSC ef029a23417 ADDR 1234 [ 4934.749079] [Hardware Error]: PROCESSOR 0:663 TIME 1317149322 SOCKET 0 APIC 0 [ 4934.749079] [Hardware Error]: Run the above through 'mcelog --ascii' [ 4934.749079] [Hardware Error]: Machine check: Overflowed uncorrected [ 4934.749079] Kernel panic - not syncing: Fatal machine check on current CPU [ 4934.749079] Pid: 1379, comm: mce-inject Tainted: G M 3.1.0-rc4.slimdump+ #34 [ 4934.749079] Call Trace: [ 4934.749079] [<ffffffff81084922>] panic+0xbc/0x1cf [ 4934.749079] [<ffffffff810858ff>] ? printk+0x6c/0x6e [ 4934.749079] [<ffffffff8104c43b>] mce_panic+0x187/0x1a4 [ 4934.749079] [<ffffffff8104d525>] do_machine_check+0x5ec/0x6c3 [ 4934.749079] [<ffffffff8104e4e1>] raise_exception+0x5c/0x84 [ 4934.749079] [<ffffffff8104e5e9>] raise_local+0x5a/0xcc [ 4934.749079] [<ffffffff8104e8ee>] mce_write+0x218/0x24e [ 4934.749079] [<ffffffff8115abee>] vfs_write+0xb0/0x108 [ 4934.749079] [<ffffffff8115ad0a>] sys_write+0x4c/0x71 [ 4934.749079] [<ffffffff815bf12b>] system_call_fastpath+0x16/0x1b [ 0.817861] kvm: no hardware support .............. ................ ................. # ls vmcore # ls -lh vmcore -r-------- 1 root root 1.8G Sep 27 13:20 vmcore # ~/makedumpfile.slimdump/makedumpfile vmcore vmcore.makedumpfile.review The kernel version is not supported. The created dumpfile may be incomplete. Copying data : [100 %] The dumpfile is saved to vmcore.makedumpfile.review. makedumpfile Completed. # ls -lh vmcore.makedumpfile.review -rw------- 1 root root 3.9K Sep 28 01:40 vmcore.makedumpfile.review # eu-readelf -n vmcore.makedumpfile.review Note segment of 3592 bytes at offset 0x158: Owner Data size Type CORE 336 PRSTATUS info.si_signo: 0, info.si_code: 0, info.si_errno: 0, cursig: 0 sigpend: <> .......... ............. ......... NUMBER(PG_private)=11 NUMBER(PG_swapcache)=16 SYMBOL(phys_base)=ffffffff81a0e010 SYMBOL(init_level4_pgt)=ffffffff81a06000 SYMBOL(node_data)=ffffffff81b70b80 LENGTH(node_data)=512 CRASHTIME=1317621133 PANIC_MCE 49 <unknown>: 21 # crash -S ~/linux-2.6.slimdump/System.map ~/linux-2.6.slimdump/vmlinux vmcore.makedumpfile.review crash 5.1.8 Copyright (C) 2002-2011 Red Hat, Inc. Copyright (C) 2004, 2005, 2006 IBM Corporation Copyright (C) 1999-2006 Hewlett-Packard Co Copyright (C) 2005, 2006 Fujitsu Limited Copyright (C) 2006, 2007 VA Linux Systems Japan K.K. Copyright (C) 2005 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. crash: overriding /boot/System.map with /home/prasadkr/linux-2.6.slimdump/System.map "System crashed due to a hardware memory error. No coredump available." Nocoredump Reason: PANIC_MCE crash: Elf64_Phdr pointer: 1c46170 ELF header end: 1c46130 ------- Thanks, K.Prasad
