From patchwork Thu Mar 5 05:21:21 2015 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: NeilBrown X-Patchwork-Id: 5943561 Return-Path: X-Original-To: patchwork-linux-fsdevel@patchwork.kernel.org Delivered-To: patchwork-parsemail@patchwork2.web.kernel.org Received: from mail.kernel.org (mail.kernel.org [198.145.29.136]) by patchwork2.web.kernel.org (Postfix) with ESMTP id 0549CBF440 for ; Thu, 5 Mar 2015 05:24:42 +0000 (UTC) Received: from mail.kernel.org (localhost [127.0.0.1]) by mail.kernel.org (Postfix) with ESMTP id 227D8202BE for ; Thu, 5 Mar 2015 05:24:41 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 317BE202B8 for ; Thu, 5 Mar 2015 05:24:40 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753248AbbCEFWt (ORCPT ); Thu, 5 Mar 2015 00:22:49 -0500 Received: from cantor2.suse.de ([195.135.220.15]:42160 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752083AbbCEFWr (ORCPT ); Thu, 5 Mar 2015 00:22:47 -0500 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (charybdis-ext.suse.de [195.135.220.254]) by mx2.suse.de (Postfix) with ESMTP id 4BDD0AC77; Thu, 5 Mar 2015 05:22:46 +0000 (UTC) From: NeilBrown To: Alexander Viro Date: Thu, 05 Mar 2015 16:21:21 +1100 Subject: [PATCH 3/9] VFS/namei: new flag to support RCU symlinks: LOOKUP_LINK_RCU. Cc: linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org Message-ID: <20150305052121.23906.84068.stgit@notabene.brown> In-Reply-To: <20150305051530.23906.65097.stgit@notabene.brown> References: <20150305051530.23906.65097.stgit@notabene.brown> User-Agent: StGit/0.17.1-dirty MIME-Version: 1.0 Sender: linux-fsdevel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org X-Spam-Status: No, score=-6.9 required=5.0 tests=BAYES_00, RCVD_IN_DNSWL_HI, T_RP_MATCHES_RCVD, UNPARSEABLE_RELAY autolearn=unavailable version=3.3.1 X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on mail.kernel.org X-Virus-Scanned: ClamAV using ClamSMTP When we support ->follow_link in RCU-walk we will not want to take a reference to the 'struct path *link' passed to follow_link, and correspondingly will not want to drop that reference. As link_path_walk will complete_walk() in the case of an error, and as complete_walk() will clear LOOKUP_RCU, we cannot test LOOKUP_RCU to determine if the path should be 'put'. So introduce a new flag: LOOKUP_LINK_RCU. This is set on entry to follow_link() if appropriate and put_link() will only call path_put() if it is clear. Also, unlazy_walk() will fail if LOOKUP_LINK_RCU is set. This is because there is no way for unlazy_walk to get references on all the "struct path *link"s that are protected by that flag. Signed-off-by: NeilBrown --- fs/namei.c | 18 +++++++++++++----- include/linux/namei.h | 1 + 2 files changed, 14 insertions(+), 5 deletions(-) -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html diff --git a/fs/namei.c b/fs/namei.c index 515adc4594be..a4879bb3b4ee 100644 --- a/fs/namei.c +++ b/fs/namei.c @@ -533,6 +533,9 @@ static int unlazy_walk(struct nameidata *nd, struct dentry *dentry) struct dentry *parent = nd->path.dentry; BUG_ON(!(nd->flags & LOOKUP_RCU)); + if (nd->flags & LOOKUP_LINK_RCU) + /* Cannot unlazy in the middle of following a symlink */ + return -ECHILD; /* * After legitimizing the bastards, terminate_walk() @@ -743,7 +746,8 @@ static inline void put_link(struct nameidata *nd, struct path *link, void *cooki struct inode *inode = link->dentry->d_inode; if (inode->i_op->put_link) inode->i_op->put_link(link->dentry, nd, cookie); - path_put(link); + if (!(nd->flags & LOOKUP_LINK_RCU)) + path_put(link); } int sysctl_protected_symlinks __read_mostly = 0; @@ -869,9 +873,10 @@ follow_link(struct path *link, struct nameidata *nd, void **p) int error; char *s; - BUG_ON(nd->flags & LOOKUP_RCU); - - if (link->mnt == nd->path.mnt) + nd->flags &= ~LOOKUP_LINK_RCU; + if (nd->flags & LOOKUP_RCU) + nd->flags |= LOOKUP_LINK_RCU; + else if (link->mnt == nd->path.mnt) mntget(link->mnt); error = -ELOOP; @@ -921,7 +926,8 @@ follow_link(struct path *link, struct nameidata *nd, void **p) out_put_nd_path: *p = NULL; terminate_walk(nd); - path_put(link); + if (!(nd->flags & LOOKUP_LINK_RCU)) + path_put(link); return error; } @@ -1644,6 +1650,8 @@ static inline int nested_symlink(struct path *path, struct nameidata *nd) current->link_count--; nd->depth--; + if (!nd->depth) + nd->flags &= ~LOOKUP_LINK_RCU; return res; } diff --git a/include/linux/namei.h b/include/linux/namei.h index c8990779f0c3..34bc87845b0e 100644 --- a/include/linux/namei.h +++ b/include/linux/namei.h @@ -32,6 +32,7 @@ enum {LAST_NORM, LAST_ROOT, LAST_DOT, LAST_DOTDOT, LAST_BIND}; #define LOOKUP_PARENT 0x0010 #define LOOKUP_REVAL 0x0020 #define LOOKUP_RCU 0x0040 +#define LOOKUP_LINK_RCU 0x0080 /* * Intent data