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authorMiklos Szeredi <mszeredi@redhat.com>2020-06-04 10:48:19 +0200
committerMiklos Szeredi <mszeredi@redhat.com>2020-06-04 10:48:19 +0200
commitdf820f8de4e481222b17f9bcee7b909ae8167529 (patch)
tree8410725a7cd85f540f59120710b8617c18348670 /fs/namespace.c
parentb8e42a651bdee06202ebdd96cff64fdeabd5b1d6 (diff)
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 <viro@zeniv.linux.org.uk> Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
Diffstat (limited to 'fs/namespace.c')
-rw-r--r--fs/namespace.c16
1 files changed, 16 insertions, 0 deletions
diff --git a/fs/namespace.c b/fs/namespace.c
index a28e4db075ed..d53517f1d741 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -1879,6 +1879,9 @@ struct vfsmount *clone_private_mount(const struct path *path)
if (IS_ERR(new_mnt))
return ERR_CAST(new_mnt);
+ /* Longterm mount to be removed by kern_unmount*() */
+ new_mnt->mnt_ns = MNT_NS_INTERNAL;
+
return &new_mnt->mnt;
}
EXPORT_SYMBOL_GPL(clone_private_mount);
@@ -3804,6 +3807,19 @@ void kern_unmount(struct vfsmount *mnt)
}
EXPORT_SYMBOL(kern_unmount);
+void kern_unmount_array(struct vfsmount *mnt[], unsigned int num)
+{
+ unsigned int i;
+
+ for (i = 0; i < num; i++)
+ if (mnt[i])
+ real_mount(mnt[i])->mnt_ns = NULL;
+ synchronize_rcu_expedited();
+ for (i = 0; i < num; i++)
+ mntput(mnt[i]);
+}
+EXPORT_SYMBOL(kern_unmount_array);
+
bool our_mnt(struct vfsmount *mnt)
{
return check_mnt(real_mount(mnt));