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authorEric W. Biederman <ebiederman@twitter.com>2013-10-03 01:31:18 -0700
committerAl Viro <viro@zeniv.linux.org.uk>2014-10-09 02:38:55 -0400
commit80b5dce8c59b0de1ed6e403b8298e02dcb4db64b (patch)
tree90b7a4f30c050d37f7ec436b63c8f9d7816199f0
parente2dfa935464272395b4f35f4cc74ffcc87418b84 (diff)
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>
-rw-r--r--fs/mount.h9
-rw-r--r--fs/namespace.c31
2 files changed, 40 insertions, 0 deletions
diff --git a/fs/mount.h b/fs/mount.h
index 68bb03ed7f19..f82c62840905 100644
--- a/fs/mount.h
+++ b/fs/mount.h
@@ -87,6 +87,15 @@ extern struct mount *__lookup_mnt_last(struct vfsmount *, struct dentry *);
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);
diff --git a/fs/namespace.c b/fs/namespace.c
index 88fc3f4d77ed..00e5b1efa591 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -1468,6 +1468,37 @@ static int do_umount(struct mount *mnt, int flags)
return retval;
}
+/*
+ * __detach_mounts - lazily unmount all mounts on the specified dentry
+ *
+ * During unlink, rmdir, and d_drop it is possible to loose the path
+ * to an existing mountpoint, and wind up leaking the mount.
+ * detach_mounts allows lazily unmounting those mounts instead of
+ * leaking them.
+ *
+ * The caller may hold dentry->d_inode->i_mutex.
+ */
+void __detach_mounts(struct dentry *dentry)
+{
+ struct mountpoint *mp;
+ struct mount *mnt;
+
+ namespace_lock();
+ mp = lookup_mountpoint(dentry);
+ if (!mp)
+ goto out_unlock;
+
+ lock_mount_hash();
+ while (!hlist_empty(&mp->m_list)) {
+ mnt = hlist_entry(mp->m_list.first, struct mount, mnt_mp_list);
+ umount_tree(mnt, 2);
+ }
+ unlock_mount_hash();
+ put_mountpoint(mp);
+out_unlock:
+ namespace_unlock();
+}
+
/*
* Is the caller allowed to modify his namespace?
*/