Red Hat Bugzilla – Bug 820116
vgcfgrestore fails with division by zero if PV with zero length present in VG
Last modified: 2013-02-21 03:09:46 EST
Description of problem: If there is PV with zero PE count in the VG, vgcfgrestore on the VG fails saying "Floating point exception", which is caused by division by zero. Background: We are using LVM heavily for storage of block device backups. Because the PVs are usually very busy and metadata manipulation requires direct access to the metadata sector (may take considerable time to complete), we have created a metadata-only PV on a separate drive. Version-Release number of selected component (if applicable): LVM version: 2.02.87(2)-RHEL6 (2011-10-12) Library version: 1.02.66-RHEL6 (2011-10-12) Driver version: 4.22.6 How reproducible: Always Steps to Reproduce: create /dev/<metadata_device> with size 200M create /dev/<data_device> of any size pvcreate --metadatasize 128m /dev/<metadata_device> pvcreate --metadatasize 128m /dev/<data_device> vgcreate -s 128m myVG /dev/<metadata_device> /dev/<data_device> vgcfgbackup myVG vgcfgrestore myVG Actual results: Last command fails with "Floating point exception" error. Expected results: vgcfgrestore should successfully write VG metadata Additional info: This issue may be worked around by omitting the zero-length PV from the backup file. See file contents below. We have solved this for our case using the above workaround and making the metadata PV bigger and setting allocable to N afterwards. Backup file contents: # Generated by LVM2 version 2.02.87(2)-RHEL6 (2011-10-12): Wed May 9 10:13:28 2012 contents = "Text Format Volume Group" version = 1 description = "vgcfgbackup -f myvg.vg myvg" creation_host = "localhost.localdomain" # Linux localhost.localdomain 2.6.32-220.el6.x86_64 #1 SMP Tue Dec 6 19:48:22 GMT 2011 x86_64 creation_time = 1336551208 # Wed May 9 10:13:28 2012 myvg { id = "ouGQeP-8bPl-udT8-lm8a-Nd3A-WprB-pOGXfj" seqno = 1 status = ["RESIZEABLE", "READ", "WRITE"] flags = [] extent_size = 262144 # 128 Megabytes max_lv = 0 max_pv = 0 metadata_copies = 0 physical_volumes { pv0 { id = "hbMvQA-zTeD-CKPc-WE8o-umlm-Z6GJ-iyALRr" device = "/dev/vg_test/pv1" # Hint only status = ["ALLOCATABLE"] flags = [] dev_size = 20971520 # 10 Gigabytes pe_start = 264192 pe_count = 78 # 9.75 Gigabytes } pv1 { id = "K1BwfU-2LuG-8aeW-IXHR-RLf7-d36V-DMERDr" device = "/dev/vg_test/pv_metadata" # Hint only status = ["ALLOCATABLE"] flags = [] dev_size = 409600 # 200 Megabytes pe_start = 264192 pe_count = 0 # 0 Kilobytes } } } Backup file for workaround: # Generated by LVM2 version 2.02.87(2)-RHEL6 (2011-10-12): Wed May 9 10:13:28 2012 contents = "Text Format Volume Group" version = 1 description = "vgcfgbackup -f myvg.vg myvg" creation_host = "localhost.localdomain" # Linux localhost.localdomain 2.6.32-220.el6.x86_64 #1 SMP Tue Dec 6 19:48:22 GMT 2011 x86_64 creation_time = 1336551208 # Wed May 9 10:13:28 2012 myvg { id = "ouGQeP-8bPl-udT8-lm8a-Nd3A-WprB-pOGXfj" seqno = 1 status = ["RESIZEABLE", "READ", "WRITE"] flags = [] extent_size = 262144 # 128 Megabytes max_lv = 0 max_pv = 0 metadata_copies = 0 physical_volumes { pv0 { id = "hbMvQA-zTeD-CKPc-WE8o-umlm-Z6GJ-iyALRr" device = "/dev/vg_test/pv1" # Hint only status = ["ALLOCATABLE"] flags = [] dev_size = 20971520 # 10 Gigabytes pe_start = 264192 pe_count = 78 # 9.75 Gigabytes } } }
Thanks for reporting this! Peter has committed a fix for the next upstream release (2.02.96) and this will be picked up by RHEL6.4: http://sourceware.org/git/?p=lvm2.git;a=commitdiff;h=501a2c04a4cb009a4c6497cd601801b2fe32fb4e
Tested with old and new versioni of lvm2. With older version the core dumps as expected (reported by BZ): Syncing disks. (09:15:44) [root@r6-node02:~]$ pvcreate --metadatasize 128m /dev/sde1 Writing physical volume data to disk "/dev/sde1" Physical volume "/dev/sde1" successfully created (09:15:55) [root@r6-node02:~]$ pvcreate --metadatasize 128m /dev/sdf1 Writing physical volume data to disk "/dev/sdf1" Physical volume "/dev/sdf1" successfully created (09:15:58) [root@r6-node02:~]$ vgcreate -s 128m myvg2 /dev/sde1 /dev/sdf1 Volume group "myvg2" successfully created (09:16:12) [root@r6-node02:~]$ pvs PV VG Fmt Attr PSize PFree /dev/sdb1 myvg lvm2 a-- 9.75g 9.75g /dev/sdc1 myvg lvm2 a-- 200.98m 200.98m /dev/sde1 myvg2 lvm2 a-- 199.98m 199.98m /dev/sdf1 myvg2 lvm2 a-- 9.75g 9.75g /dev/vda2 VolGroup lvm2 a-- 8.51g 0 (09:16:14) [root@r6-node02:~]$ vgcfgbackup myvg2 Volume group "myvg2" successfully backed up. (09:16:48) [root@r6-node02:~]$ vgcfgrestore myvg2 Floating point exception (core dumped) ---------------------------------------------------------------------------- With the new version of lvm it works normally: (09:12:13) [root@r6-node01:/etc/yum.repos.d]$ pvcreate --metadatasize 128m /dev/sdb sdb sdb1 (09:12:13) [root@r6-node01:/etc/yum.repos.d]$ pvcreate --metadatasize 128m /dev/sdb sdb sdb1 (09:12:13) [root@r6-node01:/etc/yum.repos.d]$ pvcreate --metadatasize 128m /dev/sdb1 Physical volume "/dev/sdb1" successfully created (09:12:48) [root@r6-node01:/etc/yum.repos.d]$ vgcreate -s 128m myvg /dev/sda1 /dev/sdb1 Volume group "myvg" (09:13:17) [root@r6-node01:/etc/yum.repos.d]$ vgcfgbackup myvg Volume group "myvg" successfully backed up. successfully created (09:13:59) [root@r6-node01:/etc/lvm/backup]$ vgcfgrestore myvg Restored volume group myvg (09:14:09) [root@r6-node01:/etc/lvm/backup]$ Packages installed: lvm2-2.02.95-10.el6.x86_64 device-mapper-1.02.74-10.el6.x86_64 kernel-2.6.32-279.el6.x86_64
Since the problem described in this bug report should be resolved in a recent advisory, it has been closed with a resolution of ERRATA. For information on the advisory, and where to find the updated files, follow the link below. If the solution does not work for you, open a new bug report. http://rhn.redhat.com/errata/RHBA-2013-0501.html