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Nened just verified this happens only when running the two commands in close sequence like this:
echo offline > /sys/block/sda/device/state && pvscan --cache /dev/sda1
May not be very likely to happen... Could it be inherent to ANY parallel scans?
No, other parallel scans are unaffected -- it is only lvscan that is susceptible. This is because lvscan relies on device information from lvmetad. A lvmetad debug log would be very useful here (with -l wire) -- but as far as I can tell, the problem is not parallel scans at all -- dmeventd should crash the same way when any LV that is already partial is rescanned. I'll write a testcase for that and see if that's the case.
The problem is that lvscan --cache uses device information from lvmetad, which may be already partial if pvscan --cache finishes before lvscan --cache can read the device info. In this case, lvscan --cache should ignore devices that are already known to be missing, instead of trying to scan them again (and encountering a null pointer).
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-2014-1387.html
Description of problem: Segfaulting dmeventd. Version-Release number of selected component (if applicable): lvm2-2.02.108-1.el6.x86_64 kernel-2.6.32-494.el6.x86_64 How reproducible: 100% Steps to Reproduce: sda1 is a leg in RAID LV. Though likely irrelevant the raid_fault_policy is warn. Executing these two commands: echo offline > /sys/block/sda/device/state pvscan --cache /dev/sda1 Results in segfault in dmeventd. Messages: Jul 31 17:41:44 barb-02c1-node01 kernel: sd 2:0:0:0: rejecting I/O to offline device Jul 31 17:41:44 barb-02c1-node01 kernel: end_request: I/O error, dev sda, sector 0 Jul 31 17:41:44 barb-02c1-node01 kernel: sd 2:0:0:0: rejecting I/O to offline device Jul 31 17:41:44 barb-02c1-node01 kernel: end_request: I/O error, dev sda, sector 0 Jul 31 17:41:44 barb-02c1-node01 kernel: sd 2:0:0:0: rejecting I/O to offline device Jul 31 17:41:44 barb-02c1-node01 kernel: md: super_written gets error=-5, uptodate=0 Jul 31 17:41:44 barb-02c1-node01 kernel: md/raid10:mdX: Disk failure on dm-9, disabling device. Jul 31 17:41:44 barb-02c1-node01 kernel: md/raid10:mdX: Operation continuing on 5 devices. Jul 31 17:41:44 barb-02c1-node01 lvm[10528]: Device #4 of raid10 array, black_bird-synced_random_raid10_3legs_1, has failed. Jul 31 17:41:44 barb-02c1-node01 kernel: sd 2:0:0:0: rejecting I/O to offline device Jul 31 17:41:44 barb-02c1-node01 kernel: md: super_written gets error=-5, uptodate=0 Jul 31 17:41:44 barb-02c1-node01 lvm[10528]: PV mkHEgE-rMpc-w6eY-3y0r-Qce7-Cy1G-COvwAi not recognised. Is the device missing? Jul 31 17:41:44 barb-02c1-node01 kernel: dmeventd[10531]: segfault at 50 ip 00007f1f2e1660e7 sp 00007f1f2f0fc398 error 4 in libc-2.12.so[7f1f2e0d8000+18b000]