From: Tao Cui File locks and leases taken on files through the overlay mount are only meaningful between tasks that access the files through the same overlay mount; they do not conflict with anything that changes the underlying filesystems directly. Add a short note to "Changes to underlying filesystems" stating this scope. Signed-off-by: Tao Cui --- Changes since v1: - minimal note within "Changes to underlying filesystems" instead of a separate section, per review (Amir Goldstein) --- Documentation/filesystems/overlayfs.rst | 9 +++++++++ 1 file changed, 9 insertions(+) diff --git a/Documentation/filesystems/overlayfs.rst b/Documentation/filesystems/overlayfs.rst index 16c35b491dad..11af5bc73e32 100644 --- a/Documentation/filesystems/overlayfs.rst +++ b/Documentation/filesystems/overlayfs.rst @@ -671,6 +671,15 @@ filesystem are not allowed. If the underlying filesystem is changed, the behavior of the overlay is undefined, though it will not result in a crash or deadlock. +Note that file locks and leases taken on files through the overlay +mount only provide mutual exclusion between tasks that access the +files through the same overlay mount, and a lease taken through the +overlay is broken by opens through that overlay. They do not +conflict with locks taken on the same files by anything that changes +the underlying filesystems directly, so file locking cannot be relied +on for mutual exclusion between overlay users and such direct +changes. + Offline changes, when the overlay is not mounted, are allowed to the upper tree. Offline changes to the lower tree are only allowed if the "metacopy", "index", "xino" and "redirect_dir" features -- 2.43.0