linux-kernel - Re: [PATCH 2/2] vfs: force reval on dentry of bind mounted files on FS_REVAL

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Date:	Thu, 03 Dec 2009 03:56:41 -0800
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	Miklos Szeredi <miklos@...redi.hu>
Cc:	jlayton@...hat.com, linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org, jamie@...reable.org, pavel@....cz,
	viro@...IV.linux.org.uk, duaneg@...da.com
Subject: Re: [PATCH 2/2] vfs: force reval on dentry of bind mounted files on FS_REVAL_DOT filesystems

Miklos Szeredi <miklos@...redi.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



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