From mboxrd@z Thu Jan 1 00:00:00 1970 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=-9.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, USER_AGENT_GIT autolearn=unavailable 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 1F770C3F2D4 for ; Sun, 1 Mar 2020 21:53:12 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id F0E98246BF for ; Sun, 1 Mar 2020 21:53:11 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727350AbgCAVxK (ORCPT ); Sun, 1 Mar 2020 16:53:10 -0500 Received: from zeniv.linux.org.uk ([195.92.253.2]:41756 "EHLO ZenIV.linux.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727209AbgCAVwv (ORCPT ); Sun, 1 Mar 2020 16:52:51 -0500 Received: from viro by ZenIV.linux.org.uk with local (Exim 4.92.3 #3 (Red Hat Linux)) id 1j8WW1-003fQy-Mq; Sun, 01 Mar 2020 21:52:49 +0000 From: Al Viro To: linux-fsdevel@vger.kernel.org Cc: linux-kernel@vger.kernel.org, Linus Torvalds Subject: [RFC][PATCH v3 54/55] non-RCU analogue of the previous commit Date: Sun, 1 Mar 2020 21:52:39 +0000 Message-Id: <20200301215240.873899-54-viro@ZenIV.linux.org.uk> X-Mailer: git-send-email 2.24.1 In-Reply-To: <20200301215240.873899-1-viro@ZenIV.linux.org.uk> References: <20200301215125.GA873525@ZenIV.linux.org.uk> <20200301215240.873899-1-viro@ZenIV.linux.org.uk> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Al Viro new helper: choose_mountpoint(). Wrapper around choose_mountpoint_rcu(), similar to lookup_mnt() vs. __lookup_mnt(). follow_dotdot() switched to it. Now we don't grab mount_lock exclusive anymore; note that the primitive used non-RCU mount traversals in other direction (lookup_mnt()) doesn't bother with that either - it uses mount_lock seqcount instead. Signed-off-by: Al Viro --- fs/namei.c | 56 +++++++++++++++++++++++++++++++++++++++----------------- 1 file changed, 39 insertions(+), 17 deletions(-) diff --git a/fs/namei.c b/fs/namei.c index 8c09523c6f56..f247eca119f1 100644 --- a/fs/namei.c +++ b/fs/namei.c @@ -605,10 +605,9 @@ static void terminate_walk(struct nameidata *nd) } /* path_put is needed afterwards regardless of success or failure */ -static bool legitimize_path(struct nameidata *nd, - struct path *path, unsigned seq) +static bool __legitimize_path(struct path *path, unsigned seq, unsigned mseq) { - int res = __legitimize_mnt(path->mnt, nd->m_seq); + int res = __legitimize_mnt(path->mnt, mseq); if (unlikely(res)) { if (res > 0) path->mnt = NULL; @@ -622,6 +621,12 @@ static bool legitimize_path(struct nameidata *nd, return !read_seqcount_retry(&path->dentry->d_seq, seq); } +static inline bool legitimize_path(struct nameidata *nd, + struct path *path, unsigned seq) +{ + return __legitimize_path(path, nd->m_seq, seq); +} + static bool legitimize_links(struct nameidata *nd) { int i; @@ -1383,6 +1388,31 @@ static bool choose_mountpoint_rcu(struct mount *m, const struct path *root, return false; } +static bool choose_mountpoint(struct mount *m, const struct path *root, + struct path *path) +{ + bool found; + + rcu_read_lock(); + while (1) { + unsigned seq, mseq = read_seqbegin(&mount_lock); + + found = choose_mountpoint_rcu(m, root, path, &seq); + if (unlikely(!found)) { + if (!read_seqretry(&mount_lock, mseq)) + break; + } else { + if (likely(__legitimize_path(path, seq, mseq))) + break; + rcu_read_unlock(); + path_put(path); + rcu_read_lock(); + } + } + rcu_read_unlock(); + return found; +} + /* * Skip to top of mountpoint pile in refwalk mode for follow_dotdot() */ @@ -1758,22 +1788,14 @@ static struct dentry *follow_dotdot(struct nameidata *nd, if (path_equal(&nd->path, &nd->root)) goto in_root; if (unlikely(nd->path.dentry == nd->path.mnt->mnt_root)) { - struct path path = nd->path; - path_get(&path); - while (1) { - if (!follow_up(&path)) { - path_put(&path); - goto in_root; - } - if (path_equal(&path, &nd->root)) { - path_put(&path); - goto in_root; - } - if (path.dentry != nd->path.mnt->mnt_root) - break; - } + struct path path; + + if (!choose_mountpoint(real_mount(nd->path.mnt), + &nd->root, &path)) + goto in_root; path_put(&nd->path); nd->path = path; + nd->inode = path.dentry->d_inode; if (unlikely(nd->flags & LOOKUP_NO_XDEV)) return ERR_PTR(-EXDEV); } -- 2.11.0