Q. locking order of dcache_lru_lock

["J. R. Okajima" <hooanon05@yahoo.co.jp>]

Hello Al Viro, Christoph Hellwig and Nick Piggin,

I have a question about the locking order of dcache_lru_lock.

The comment in fs/dcache.c says
 * Ordering:
 * dentry->d_inode->i_lock
 *   dentry->d_lock
 *     dcache_lru_lock
	:::

d_lock should be before dcache_lru_lock.
Actually dentry_lru_(add|del|move_tail) functions (and their callers) do
it expectedly.
But __shrink_dcache_sb() looks different.

__shrink_dcache_sb()
{
	:::
relock:
	spin_lock(&dcache_lru_lock);
	while (!list_empty(&sb->s_dentry_lru)) {
		::
		if (!spin_trylock(&dentry->d_lock)) {
			spin_unlock(&dcache_lru_lock);
			cpu_relax();
			goto relock;
		}
	:::
}

When spin_trylock(&dentry->d_lock) successfully acquired d_lock, does
the violation of locking order happen (or a deadlock, in worse case)?

By the way, the code is introduced by the commit
	2304450 2011-01-07 fs: dcache scale lru
by Nick Piggin.
Is he allright? Does anyone know anything?
We have not received from him for a long time.


J. R. Okajima