[PATCH] knfsd: nfsd: oops exporting nonexistent directory

Export a directory that does not exist:
	exportfs -orw,fsid=0,insecure,no_subtree_check client:/home/NFS4

Try to mount from client with nfs4. Mount hangs (I'm not sure why -
that's another issue).

While client is hung, back on server

	mkdir /home/NFS4

The server panics in dput.  I traced the problem back to svc_export_parse()
calling path_release() even though path_lookup() failed (it happens to fill in
the nameidata structure with a negative dentry - so the test after out:
succeeds).

After patching, an recreating the problem, the client mount still takes some
time before finally exiting with a message "couldn't read superblock".

Here is a simple patch to resolve this issue:
Signed-off-by: NFrank Filz <ffilzlnx@us.ibm.com>
Signed-off-by: NJ. Bruce Fields <bfields@citi.umich.edu>
Signed-off-by: NNeil Brown <neilb@suse.de>
Signed-off-by: NAndrew Morton <akpm@osdl.org>
Signed-off-by: NLinus Torvalds <torvalds@osdl.org>

fs/nfsd/export.c

@@ -422,7 +422,7 @@ static int svc_export_parse(struct cache_detail *cd, char *mesg, int mlen)
 	if ((len=qword_get(&mesg, buf, PAGE_SIZE)) <= 0)
 		goto out;
 	err = path_lookup(buf, 0, &nd);
-	if (err) goto out;
+	if (err) goto out_no_path;
 
 	exp.h.flags = 0;
 	exp.ex_client = dom;
@@ -475,6 +475,7 @@ static int svc_export_parse(struct cache_detail *cd, char *mesg, int mlen)
  out:
 	if (nd.dentry)
 		path_release(&nd);
+ out_no_path:
 	if (dom)
 		auth_domain_put(dom);
 	kfree(buf);