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Subject[PATCH 05/11] vfs: Add a function to lazily unmount all mounts from any dentry.

v2: Always drop the lock when exiting early.
v3: Make detach_mounts robust about freeing several
mounts on the same mountpoint at one time, and remove
the unneeded mnt_list list test.
v4: Document the purpose of detach_mounts and why new_mountpoint is
safe to call.

Signed-off-by: Eric W. Biederman <ebiederman@twitter.com>
---
fs/mount.h | 2 ++
fs/namespace.c | 39 +++++++++++++++++++++++++++++++++++++++
2 files changed, 41 insertions(+), 0 deletions(-)

diff --git a/fs/mount.h b/fs/mount.h
index 50a72d46e7a6..2b470f34e665 100644
--- a/fs/mount.h
+++ b/fs/mount.h
@@ -84,6 +84,8 @@ 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 get_mnt_ns(struct mnt_namespace *ns)
{
atomic_inc(&ns->count);
diff --git a/fs/namespace.c b/fs/namespace.c
index 33db9e95bd5c..7abbf722ce18 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -1359,6 +1359,45 @@ 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();
+ if (!d_mountpoint(dentry))
+ goto out_unlock;
+
+ /*
+ * The namespace lock and d_mountpoint being set guarantees
+ * that new_mountpoint will just be a lookup of the existing
+ * mountpoint structure.
+ */
+ mp = new_mountpoint(dentry);
+ if (IS_ERR(mp))
+ goto out_unlock;
+
+ lock_mount_hash();
+ while (!list_empty(&mp->m_list)) {
+ mnt = list_first_entry(&mp->m_list, struct mount, mnt_mp_list);
+ umount_tree(mnt, 1);
+ }
+ unlock_mount_hash();
+ put_mountpoint(mp);
+out_unlock:
+ namespace_unlock();
+}
+
/*
* Is the caller allowed to modify his namespace?
*/
--
1.7.5.4


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