Re: Q: NFSD readdir in linux-2.6.28

[J. Bruce Fields]

On Thu, Mar 19, 2009 at 03:17:17PM +0000, David Woodhouse wrote:
> On Thu, 2009-03-19 at 14:54 +0000, hooanon05@xxxxxxxxxxx wrote:
> > 
> > Hello David and Al,
> > I have a question about NFSD readdir.
> > 
> > By the commit 14f7dd632011bb89c035722edd6ea0d90ca6b078
> > "[PATCH] Copy XFS readdir hack into nfsd code", nfsd_buffered_filldir()
> > was introduced and nfs3svc_encode_entry_plus() (the 'func' parameter) is
> > not called from vfs_readdir().
> > 
> > In 2.6.27, when nfs3svc_encode_entry_plus() calls lookup_one_len(), the
> > i_mutex lock was acquired by vfs_readdir() and it was not a problem.
> > 
> > After the commit (above), nfsd_readdir/nfsd_buffered_readdir/vfs_readdir
> > calls nfsd_buffered_filldir(), and nfs3svc_encode_entry_plus() is called
> > later.
> > In this sequence, lookup_one_len() is called without i_mutex held.
> > 
> > Isn't it a problem?
> 
> 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...

Yipes--is this problem still here?

--b.
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