From patchwork Wed Dec 9 20:24:03 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Steven Rostedt X-Patchwork-Id: 11962483 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-15.2 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_2 autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id C8EF5C4361B for ; Wed, 9 Dec 2020 20:25:09 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 878CB23C92 for ; Wed, 9 Dec 2020 20:25:09 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2387544AbgLIUY7 (ORCPT ); Wed, 9 Dec 2020 15:24:59 -0500 Received: from mail.kernel.org ([198.145.29.99]:36846 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1733214AbgLIUYq (ORCPT ); Wed, 9 Dec 2020 15:24:46 -0500 Received: from gandalf.local.home (cpe-66-24-58-225.stny.res.rr.com [66.24.58.225]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 440F023A33; Wed, 9 Dec 2020 20:24:05 +0000 (UTC) Date: Wed, 9 Dec 2020 15:24:03 -0500 From: Steven Rostedt To: LKML Cc: Al Viro , linux-fsdevel@vger.kernel.org Subject: fs/namei.c: Make status likely to be ECHILD in lookup_fast() Message-ID: <20201209152403.6d6cf9ba@gandalf.local.home> X-Mailer: Claws Mail 3.17.3 (GTK+ 2.24.32; x86_64-pc-linux-gnu) MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org From: Steven Rostedt (VMware) Running my yearly branch profiling code, it detected a 100% wrong branch condition in name.c for lookup_fast(). The code in question has: status = d_revalidate(dentry, nd->flags); if (likely(status > 0)) return dentry; if (unlazy_child(nd, dentry, seq)) return ERR_PTR(-ECHILD); if (unlikely(status == -ECHILD)) /* we'd been told to redo it in non-rcu mode */ status = d_revalidate(dentry, nd->flags); If the status of the d_revalidate() is greater than zero, then the function finishes. Otherwise, if it is an "unlazy_child" it returns with -ECHILD. After the above two checks, the status is compared to -ECHILD, as that is what is returned if the original d_revalidate() needed to be done in a non-rcu mode. Especially this path is called in a condition of: if (nd->flags & LOOKUP_RCU) { And most of the d_revalidate() functions have: if (flags & LOOKUP_RCU) return -ECHILD; It appears that that is the only case that this if statement is triggered on two of my machines, running in production. Signed-off-by: Steven Rostedt (VMware) diff --git a/fs/namei.c b/fs/namei.c index d4a6dd772303..8dd734efae9b 100644 --- a/fs/namei.c +++ b/fs/namei.c @@ -1495,7 +1495,7 @@ static struct dentry *lookup_fast(struct nameidata *nd, return dentry; if (unlazy_child(nd, dentry, seq)) return ERR_PTR(-ECHILD); - if (unlikely(status == -ECHILD)) + if (likely(status == -ECHILD)) /* we'd been told to redo it in non-rcu mode */ status = d_revalidate(dentry, nd->flags); } else {