|author||Amir Goldstein <firstname.lastname@example.org>||2017-09-29 10:21:21 +0300|
|committer||Miklos Szeredi <email@example.com>||2017-10-05 15:53:18 +0200|
ovl: fix regression caused by exclusive upper/work dir protection
Enforcing exclusive ownership on upper/work dirs caused a docker regression: https://github.com/moby/moby/issues/34672. Euan spotted the regression and pointed to the offending commit. Vivek has brought the regression to my attention and provided this reproducer: Terminal 1: mount -t overlay -o workdir=work,lowerdir=lower,upperdir=upper none merged/ Terminal 2: unshare -m Terminal 1: umount merged mount -t overlay -o workdir=work,lowerdir=lower,upperdir=upper none merged/ mount: /root/overlay-testing/merged: none already mounted or mount point busy To fix the regression, I replaced the error with an alarming warning. With index feature enabled, mount does fail, but logs a suggestion to override exclusive dir protection by disabling index. Note that index=off mount does take the inuse locks, so a concurrent index=off will issue the warning and a concurrent index=on mount will fail. Documentation was updated to reflect this change. Fixes: 2cac0c00a6cd ("ovl: get exclusive ownership on upper/work dirs") Cc: <firstname.lastname@example.org> # v4.13 Reported-by: Euan Kemp <email@example.com> Reported-by: Vivek Goyal <firstname.lastname@example.org> Signed-off-by: Amir Goldstein <email@example.com> Signed-off-by: Miklos Szeredi <firstname.lastname@example.org>
Diffstat (limited to 'Documentation')
1 files changed, 4 insertions, 1 deletions
diff --git a/Documentation/filesystems/overlayfs.txt b/Documentation/filesystems/overlayfs.txt
index 36f528a7fdd6..8caa60734647 100644
@@ -210,8 +210,11 @@ path as another overlay mount and it may use a lower layer path that is
beneath or above the path of another overlay lower layer path.
Using an upper layer path and/or a workdir path that are already used by
-another overlay mount is not allowed and will fail with EBUSY. Using
+another overlay mount is not allowed and may fail with EBUSY. Using
partially overlapping paths is not allowed but will not fail with EBUSY.
+If files are accessed from two overlayfs mounts which share or overlap the
+upper layer and/or workdir path the behavior of the overlay is undefined,
+though it will not result in a crash or deadlock.
Mounting an overlay using an upper layer path, where the upper layer path
was previously used by another mounted overlay in combination with a