vfs: Add a function to lazily unmount all mounts from any dentry.
The new function detach_mounts comes in two pieces. The first piece
is a static inline test of d_mounpoint that returns immediately
without taking any locks if d_mounpoint is not set. In the common
case when mountpoints are absent this allows the vfs to continue
running with it's same cacheline foot print.
The second piece of detach_mounts __detach_mounts actually does the
work and it assumes that a mountpoint is present so it is slow and
takes namespace_sem for write, and then locks the mount hash (aka
mount_lock) after a struct mountpoint has been found.
With those two locks held each entry on the list of mounts on a
mountpoint is selected and lazily unmounted until all of the mount
have been lazily unmounted.
v7: Wrote a proper change description and removed the changelog
documenting deleted wrong turns.
Signed-off-by: Eric W. Biederman <ebiederman@twitter.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
diff --git a/fs/mount.h b/fs/mount.h
index 68bb03e..f82c628 100644
--- a/fs/mount.h
+++ b/fs/mount.h
@@ -87,6 +87,15 @@
extern bool legitimize_mnt(struct vfsmount *, unsigned);
+extern void __detach_mounts(struct dentry *dentry);
+
+static inline void detach_mounts(struct dentry *dentry)
+{
+ if (!d_mountpoint(dentry))
+ return;
+ __detach_mounts(dentry);
+}
+
static inline void get_mnt_ns(struct mnt_namespace *ns)
{
atomic_inc(&ns->count);