linux-kernel - Re: Q: NFSD readdir in linux-2.6.28

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Date:	Fri, 17 Apr 2009 20:32:33 +0100
From:	Al Viro <viro@...IV.linux.org.uk>
To:	David Woodhouse <dwmw2@...radead.org>
Cc:	hooanon05@...oo.co.jp, hch@...radead.org,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>
Subject: Re: Q: NFSD readdir in linux-2.6.28

On Fri, Apr 17, 2009 at 10:32:19AM +0100, David Woodhouse wrote:
> On Fri, 2009-03-20 at 00:34 +0900, hooanon05@...oo.co.jp wrote:
> > David Woodhouse:
> > > Yes, well spotted. It didn't matter when the buffered readdir() was
> > > purely internal to XFS, because it didn't matter there that we called
> > > ->lookup() without i_mutex set. But now we're exposing arbitrary file
> > > systems to it, we need to make sure we follow the locking rules. 
> > > 
> > > I _think_ it's sufficient to make the affected callers of
> > > lookup_one_len() lock the parent's i_mutex for themselves before calling
> > > it. I'll take a closer look...
> > 
> > If you remember why you discarded the FS_NO_LOOKUP_IN_READDIR flag
> > approach, please let me know. URL or something is enough.
> 
> I think someone talked me into doing it in the interest of simplicity,
> so we confine the necessary hack into the NFS code alone and _always_
> just use the "safe" version. I can't remember who it was, but I'm
> guessing Al or Christoph -- both of whom are CC'd in case they want to
> object:

Ow...  Sorry, I've missed that one.  I really don't like flags-based
solution ;-/  It's not just filesystem method that want i_mutex there -
we have fs/namei.c code suddenly called in different locking conditions
now.

What were the details of xfs and jffs2 locking problems, just in case
if something can be done in that direction short-term?

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