On Thu, Aug 2, 2018 at 2:26 PM WGH <wgh@xxxxxxxxx> wrote: > > (I originally reported this problem here: > https://bugzilla.kernel.org/show_bug.cgi?id=200439) > > When I updated from 4.14 to 4.16, my LVM snapshotting script broke for > no apparent reason. > > My script has the following line, and it fails like this: > + lvcreate --size 5G --snapshot --name snap0 --permission r > /dev/mapper/vg0-lvol_rootfs > device-mapper: create ioctl on > vg0-snap0-cowLVM-sDdIeh9cecWdaNyRfZC31mxgfwTa4sOeHMJXVOykGVRtfP6Aii7IHvwS066AOLOM-cow > failed: Device or resource busy > Failed to lock logical volume vg0/lvol_rootfs. > Aborting. Manual intervention required. > > At the same time, some errors appear in dmesg as well: > [ 26.145279] generic_make_request: Trying to write to read-only > block-device dm-3 (partno 0) > [ 26.145288] device-mapper: persistent snapshot: write_header failed > [ 26.145847] device-mapper: table: 253:4: snapshot: Failed to read > snapshot metadata > [ 26.145851] device-mapper: ioctl: error adding target to table > > I bisected the vanilla kernel, and the first bad commit is > [721c7fc701c71f693307d274d2b346a1ecd4a534] block: fail op_is_write() > requests to read-only partitions Adding Mike and dm-devel. >From a quick look, --permission r sets DM_READONLY_FLAG, which makes dm mark the disk read-only with set_disk_ro(dm_disk(md), 1) in do_resume(). A bit later it tries to write to the disk from write_header(): return chunk_io(ps, ps->header_area, 0, REQ_OP_WRITE, 0, 1); Thanks, Ilya
