vfs: Add a function to lazily unmount all mounts from any dentry. (80b5dce8) · Commits · 戴 / test

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>

fs/mount.h

+9 −0

Original line number	Diff line number	Diff line
		@@ -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);

fs/namespace.c

+31 −0

Original line number	Diff line number	Diff line
		@@ -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?
		*/

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