CC: containers folks for feedback On Mon, Jul 15, 2019 at 4:38 PM Amir Goldstein <amir73il@xxxxxxxxx> wrote: > > Miklos, > > I was trying to think of a way forward w.r.t container runtime > mount leaks and overlayfs mount failures, see [1][2][3]. > > It does not seem reasonable to expect they will fix all the mount > leaks and that new ones will not show up. It's a hard problem to > solve. > > I posted a fix patch to mitigate the recent regression with > index=off [2], but it does not seem reasonable to hold index=on feature > hostage for eternity or until all mount leaks are fixed. > > The proposal I have come up with is to provide an API for containers > to shutdown the instance before unmount, so the leaked mounts become > "zombies" with no ability to do any harm beyond hogging resources. > > The SHUTDOWN ioctl, used by xfs/ext4/f2fs to stop any access to > underlying blockdev is implemented in overlayfs to stop any access > to underlying layers. The real objects are still referenced, but no > vfs API can be called on underlying layers. > > Naturally, SHUTDOWN releases the inuse locks to mitigate the mount > failures. > > I wrote an xfstest to verify SHUTDOWN solves the mount leak issue [5]. > > Thoughts? I had one thought myself: On kernel < v4.19 a SHUTDOWN ioctl on an overlayfs file will have a completely different consequence - the underlying fs would shutdown! So we have several options: 1. Allow SHUTDOWN only on dir inode (it's usually executed on the mount root anyway) 2. Introduce a new SHUTDOWN flag that existing no fs (kernel < v4.19) supports 3. Use one of the new mount APIs to request "umount & shutdown sb" 4. Other ideas? I personally like the compromise of option #1, but I have not spent time studying option #3 which could be better. > > Thanks, > Amir. > > [1] https://github.com/containers/libpod/issues/3540 > [2] https://github.com/moby/moby/issues/39475 > [3] https://github.com/coreos/linux/pull/339 > [4] https://github.com/amir73il/linux/commits/ovl-overlap-detect-regression-fix > [5] https://github.com/amir73il/xfstests/commit/a56d5560e404cc8052a8e47850676364b5e8c76c > > Amir Goldstein (4): > ovl: support [S|G]ETFLAGS ioctl for directories > ovl: use generic vfs_ioc_setflags_prepare() helper > ovl: add pre/post access hooks to underlying layers > ovl: add support for SHUTDOWN ioctl > > fs/overlayfs/copy_up.c | 10 +- > fs/overlayfs/dir.c | 26 +++-- > fs/overlayfs/file.c | 200 ++++++++++++++++++++++++++------------- > fs/overlayfs/inode.c | 64 +++++++++---- > fs/overlayfs/namei.c | 15 ++- > fs/overlayfs/overlayfs.h | 15 ++- > fs/overlayfs/ovl_entry.h | 7 ++ > fs/overlayfs/readdir.c | 17 +++- > fs/overlayfs/super.c | 9 +- > fs/overlayfs/util.c | 75 +++++++++++++-- > 10 files changed, 318 insertions(+), 120 deletions(-) > > -- > 2.17.1 >
