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 12:19:48 +0100
From:	Miklos Szeredi <miklos@...redi.hu>
To:	ebiederm@...ssion.com (Eric W. Biederman)
CC:	miklos@...redi.hu, 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

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).

Thanks,
Miklos
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