rpc: properly check debugfs dentry before using it

debugfs can now report an error code if something went wrong instead of
just NULL.  So if the return value is to be used as a "real" dentry, it
needs to be checked if it is an error before dereferencing it.

This is now happening because of ff9fb72bc077 ("debugfs: return error
values, not NULL"), but why debugfs files are not being created properly
is an older issue, probably one that has always been there and should
probably be looked at...

Cc: "J. Bruce Fields" <bfields@fieldses.org>
Cc: Jeff Layton <jlayton@kernel.org>
Cc: Trond Myklebust <trond.myklebust@hammerspace.com>
Cc: Anna Schumaker <anna.schumaker@netapp.com>
Cc: linux-nfs@vger.kernel.org
Cc: netdev@vger.kernel.org
Reported-by: David Howells <dhowells@redhat.com>
Tested-by: David Howells <dhowells@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>

diff --git a/net/sunrpc/debugfs.c b/net/sunrpc/debugfs.c
index 45a033329cd4a7156c41509a255e1ca1d969f2df..19bb356230edf521d78a4729e732ead121daaebd 100644 (file)
--- a/net/sunrpc/debugfs.c
+++ b/net/sunrpc/debugfs.c
@@ -146,7 +146,7 @@ rpc_clnt_debugfs_register(struct rpc_clnt *clnt)
        rcu_read_lock();
        xprt = rcu_dereference(clnt->cl_xprt);
        /* no "debugfs" dentry? Don't bother with the symlink. */
-       if (!xprt->debugfs) {
+       if (IS_ERR_OR_NULL(xprt->debugfs)) {
                rcu_read_unlock();
                return;
        }