On Thu, Nov 29, 2012 at 05:54:02PM -0800, Patrick McLean wrote:
> > Very interesting. Do you have anything mounted on the corresponding
> > directories on server? The picture looks like you are getting empty
> > fhandles in readdir+ respons for exactly the same directories that happen
> > to be mountpoints on client. In any case, we shouldn't do that blind
> > d_drop() - empty fhandles can happen. The only remaining question is
> > why do they happen on that set of entries. From my reading of
> > encode_entryplus_baggage() it looks like we have compose_entry_fh()
> > failing for those entries and those entries alone. One possible cause
> > would be d_mountpoint(dchild) being true on server. If it is true, we
> > can declare the case closed; if not, I really wonder what's going on.
>
> Those directories do have the server's own copies of the said directories bind mounted at the moment in a separate mount namespace.
>
> Unmounting those directories on the server does appear to stop the WARN_ON from triggering.
OK, that settles it. WARN_ON() and printks in the area can be dropped;
the right fix is below. However, there's a similar place in cifs that
also needs to be dealt with and I really, really wonder why the hell do
we do d_drop() in nfs_revalidate_lookup(). It's not relevant in this
bug, but I would like to understand what's wrong with simply returning
0 from ->d_revalidate() and letting the caller (in fs/namei.c) take care
of unhashing, etc. itself. Would make have_submounts() in there pointless
as well - we could just return 0 and let d_invalidate() take care of the
checks... Trond?
diff --git a/fs/nfs/dir.c b/fs/nfs/dir.c
--- a/fs/nfs/dir.c
+++ b/fs/nfs/dir.c
@@ -450,7 +450,8 @@ void nfs_prime_dcache(struct dentry *parent, struct nfs_entry *entry)
nfs_refresh_inode(dentry->d_inode, entry->fattr);
goto out;
} else {
- d_drop(dentry);
+ if (d_invalidate(dentry) != 0)
+ goto out;
dput(dentry);
}
}
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