Messages in this thread | | | Subject | Re: Q: NFSD readdir in linux-2.6.28 | From | David Woodhouse <> | Date | Thu, 19 Mar 2009 15:17:17 +0000 |
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On Thu, 2009-03-19 at 14:54 +0000, hooanon05@yahoo.co.jp 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...
-- David Woodhouse Open Source Technology Centre David.Woodhouse@intel.com Intel Corporation
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