Re: [PATCH 2/2] vfs: force reval on dentry of bind mounted files on FS_REVAL_DOT filesystems

[ebiederm@xmission.com (Eric W. Biederman)]

Miklos Szeredi <miklos@szeredi.hu> writes:

> On Thu, 03 Dec 2009, Eric W. Biederman wrote:
>> > The only worry I have is that this adds an extra branch in a very hot
>> > codepath (do_lookup).  An error can't be returned, as you note, and
>> > for bind mounted directories d_invalidate() will not succeed: the
>> > directory is busy, it's referenced by the mount. 
>> 
>> Not true.  d_mountpoint is false, so d_invalidate can succeed.
>
> Have a look at the code.  d_invalidate() doesn't check for a
> mountpoint, it checks the refcount.  It needs to keep the directory
> dentry hashed if it's in any way reachable other than from the cache
> (file descriptor, cwd, mount, etc).

Ah.  I thought you were thinking about the mandatory have_submounts()
check in dentry->d_op->d_revalidate().

I expect the generic d_invalidate will simply hit the:
	spin_lock(&dcache_lock);
	if (d_unhashed(dentry)) {
		spin_unlock(&dcache_lock);
		return 0;
	}

After the distributed filesystem has called d_drop in
dentry->d_op->d_revalidate (when appropriate.

Eric