On 08/03/2018 12:32 AM, WGH wrote: > On 08/02/2018 09:32 PM, Linus Torvalds wrote: >> WGH (sorry, no idea what your real name is) - what's the source of the >> script that broke? Was it some system script you got from outside and >> likely to affect others too? >> >> Or was it just some local thing you wrote yourself and was >> unintentionally buggy and nobody else is likely to hit this? >> >> Because if the latter, if you can work around it and you're the only >> user this hits, we might just be able to ignore it. > The script in question is written by me and contains literally two lines: > > lvcreate --size 5G --snapshot --name snap0 --permission r > /dev/mapper/vg0-lvol_rootfs > mount /dev/mapper/vg0-snap0 /mnt/rootfs_snapshot > > The script is not buggy (I think), it was written under simple > assumption that --permission r works. And it does - unless you happen to > have combination of kernel >=4.16 and lvm2 <2.02.178. > > The commit in question appeared only in 4.16, and this kernel version is > not widespread yet. You have to be running both recent kernel and > not-so-recent lvm2 to be bitten by this. This probably explains why no > one else reported this problem. > > Workaround certainly exists: I can just create read-write snapshot, but > mount it read-only. The reason why I didn't discover the workaround > earlier is that after unsuccessful read-only snapshot creation system > ends up in some weird state where read-write snapshots are also failing > with the same error (until reboot). So I got a wrong impression that > read-write snapshots were broken as well. > I've just found one public report of this bug, though: https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=900442
