From df820f8de4e481222b17f9bcee7b909ae8167529 Mon Sep 17 00:00:00 2001 From: Miklos Szeredi Date: Thu, 4 Jun 2020 10:48:19 +0200 Subject: ovl: make private mounts longterm Overlayfs is using clone_private_mount() to create internal mounts for underlying layers. These are used for operations requiring a path, such as dentry_open(). Since these private mounts are not in any namespace they are treated as short term, "detached" mounts and mntput() involves taking the global mount_lock, which can result in serious cacheline pingpong. Make these private mounts longterm instead, which trade the penalty on mntput() for a slightly longer shutdown time due to an added RCU grace period when putting these mounts. Introduce a new helper kern_unmount_many() that can take care of multiple longterm mounts with a single RCU grace period. Cc: Al Viro Signed-off-by: Miklos Szeredi --- Documentation/filesystems/porting.rst | 7 +++++++ 1 file changed, 7 insertions(+) (limited to 'Documentation/filesystems/porting.rst') diff --git a/Documentation/filesystems/porting.rst b/Documentation/filesystems/porting.rst index 26c093969573..867036aa90b8 100644 --- a/Documentation/filesystems/porting.rst +++ b/Documentation/filesystems/porting.rst @@ -858,3 +858,10 @@ be misspelled d_alloc_anon(). [should've been added in 2016] stale comment in finish_open() nonwithstanding, failure exits in ->atomic_open() instances should *NOT* fput() the file, no matter what. Everything is handled by the caller. + +--- + +**mandatory** + +clone_private_mount() returns a longterm mount now, so the proper destructor of +its result is kern_unmount() or kern_unmount_array(). -- cgit v1.2.3