Re: [2.6.38] Deadlock between rename_lock and vfsmount_lock.

[Al Viro <viro@ZenIV.linux.org.uk>]

On Fri, Mar 18, 2011 at 12:07:48PM +0000, Al Viro wrote:
> lock_mount(path, follow)
> retry:
> 	lock path->dentry->d_inode
> 	if unlikely(can't mount)
> 		unlock
> 		fail
> 	grab namespace_sem
> 	if !follow || likely(lookup_mnt() returns NULL)
> 		we are done
> 	drop namespace_sem
> 	unlock
> 	drop path
> 	replace it with result of lookup_mnt() (and its ->mnt_root)
> 	goto retry;
> 
> and use that (local to fs/namespace.c) in do_add_mount()/do_move_mount()/
> do_loopback() (with follow = 1) and pivot_root() (follow = 0).  BTW,
> the lack of following in do_loopback() looks like a bug...

So's the lack of following on old in pivot_root, actually.  IOW, follow
argument is always 1...