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authorAmir Goldstein <amir73il@gmail.com>2017-09-29 10:21:21 +0300
committerMiklos Szeredi <mszeredi@redhat.com>2017-10-05 15:53:18 +0200
commit85fdee1eef1a9e48ad5716916677e0c5fbc781e3 (patch)
tree9f2096f14047af5ce55aacfc9a7b90a7f7405f09 /Documentation
parent5820dc0888d302ac05f8b91ffdf7e4e53b4fbf53 (diff)
download96b-common-85fdee1eef1a9e48ad5716916677e0c5fbc781e3.tar.gz
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: <stable@vger.kernel.org> # v4.13 Reported-by: Euan Kemp <euank@euank.com> Reported-by: Vivek Goyal <vgoyal@redhat.com> Signed-off-by: Amir Goldstein <amir73il@gmail.com> Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
Diffstat (limited to 'Documentation')
-rw-r--r--Documentation/filesystems/overlayfs.txt5
1 files changed, 4 insertions, 1 deletions
diff --git a/Documentation/filesystems/overlayfs.txt b/Documentation/filesystems/overlayfs.txt
index 36f528a7fdd6..8caa60734647 100644
--- a/Documentation/filesystems/overlayfs.txt
+++ b/Documentation/filesystems/overlayfs.txt
@@ -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