From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754600AbbDTST5 (ORCPT ); Mon, 20 Apr 2015 14:19:57 -0400 Received: from zeniv.linux.org.uk ([195.92.253.2]:34735 "EHLO ZenIV.linux.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753981AbbDTSNK (ORCPT ); Mon, 20 Apr 2015 14:13:10 -0400 From: Al Viro To: Linus Torvalds Cc: Neil Brown , linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org Subject: [PATCH 02/24] VFS: replace {, total_}link_count in task_struct with pointer to nameidata Date: Mon, 20 Apr 2015 19:12:46 +0100 Message-Id: <1429553588-24764-2-git-send-email-viro@ZenIV.linux.org.uk> X-Mailer: git-send-email 1.7.7.6 In-Reply-To: <20150420181222.GK889@ZenIV.linux.org.uk> References: <20150420181222.GK889@ZenIV.linux.org.uk> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: NeilBrown task_struct currently contains two ad-hoc members for use by the VFS: link_count and total_link_count. These are only interesting to fs/namei.c, so exposing them explicitly is poor layering. This patches replaces those with a single pointer to 'struct nameidata'. This structure represents the current filename lookup of which there can only be one per process, and is a natural place to store link_count and total_link_count. This will allow the current "nameidata" argument to all follow_link operations to be removed as current->nameidata can be used instead. As there are occasional circumstances where pathname lookup can recurse, such as through kern_path_locked, we always save and old current->nameidata (if there is one) when setting a new value, and make sure any active link_counts are preserved. follow_mount and follow_automount now get a 'struct nameidata *' rather than 'int flags' so that they can directly access link_count and total_link_count, rather than going through 'current'. Suggested-by: Al Viro Signed-off-by: NeilBrown Signed-off-by: Al Viro --- fs/namei.c | 79 +++++++++++++++++++++++++++++++++++---------------- include/linux/sched.h | 2 +- 2 files changed, 55 insertions(+), 26 deletions(-) diff --git a/fs/namei.c b/fs/namei.c index ffab2e0..bdd5067 100644 --- a/fs/namei.c +++ b/fs/namei.c @@ -501,10 +501,29 @@ struct nameidata { unsigned seq, m_seq; int last_type; unsigned depth; + int link_count, + total_link_count; struct file *base; char *saved_names[MAX_NESTED_LINKS + 1]; }; +static struct nameidata *set_nameidata(struct nameidata *p) +{ + struct nameidata *old = current->nameidata; + + current->nameidata = p; + if (p) { + if (!old) { + p->link_count = 0; + p->total_link_count = 0; + } else { + p->link_count = old->link_count; + p->total_link_count = old->total_link_count; + } + } + return old; +} + /* * Path walking has 2 modes, rcu-walk and ref-walk (see * Documentation/filesystems/path-lookup.txt). In situations when we can't @@ -862,11 +881,11 @@ follow_link(struct path *link, struct nameidata *nd, void **p) mntget(link->mnt); error = -ELOOP; - if (unlikely(current->total_link_count >= 40)) + if (unlikely(nd->total_link_count >= 40)) goto out_put_nd_path; cond_resched(); - current->total_link_count++; + nd->total_link_count++; touch_atime(link); nd_set_link(nd, NULL); @@ -965,7 +984,7 @@ EXPORT_SYMBOL(follow_up); * - return -EISDIR to tell follow_managed() to stop and return the path we * were called with. */ -static int follow_automount(struct path *path, unsigned flags, +static int follow_automount(struct path *path, struct nameidata *nd, bool *need_mntput) { struct vfsmount *mnt; @@ -985,13 +1004,13 @@ static int follow_automount(struct path *path, unsigned flags, * as being automount points. These will need the attentions * of the daemon to instantiate them before they can be used. */ - if (!(flags & (LOOKUP_PARENT | LOOKUP_DIRECTORY | - LOOKUP_OPEN | LOOKUP_CREATE | LOOKUP_AUTOMOUNT)) && + if (!(nd->flags & (LOOKUP_PARENT | LOOKUP_DIRECTORY | + LOOKUP_OPEN | LOOKUP_CREATE | LOOKUP_AUTOMOUNT)) && path->dentry->d_inode) return -EISDIR; - current->total_link_count++; - if (current->total_link_count >= 40) + nd->total_link_count++; + if (nd->total_link_count >= 40) return -ELOOP; mnt = path->dentry->d_op->d_automount(path); @@ -1005,7 +1024,7 @@ static int follow_automount(struct path *path, unsigned flags, * the path being looked up; if it wasn't then the remainder of * the path is inaccessible and we should say so. */ - if (PTR_ERR(mnt) == -EISDIR && (flags & LOOKUP_PARENT)) + if (PTR_ERR(mnt) == -EISDIR && (nd->flags & LOOKUP_PARENT)) return -EREMOTE; return PTR_ERR(mnt); } @@ -1045,7 +1064,7 @@ static int follow_automount(struct path *path, unsigned flags, * * Serialization is taken care of in namespace.c */ -static int follow_managed(struct path *path, unsigned flags) +static int follow_managed(struct path *path, struct nameidata *nd) { struct vfsmount *mnt = path->mnt; /* held by caller, must be left alone */ unsigned managed; @@ -1089,7 +1108,7 @@ static int follow_managed(struct path *path, unsigned flags) /* Handle an automount point */ if (managed & DCACHE_NEED_AUTOMOUNT) { - ret = follow_automount(path, flags, &need_mntput); + ret = follow_automount(path, nd, &need_mntput); if (ret < 0) break; continue; @@ -1474,7 +1493,7 @@ unlazy: path->mnt = mnt; path->dentry = dentry; - err = follow_managed(path, nd->flags); + err = follow_managed(path, nd); if (unlikely(err < 0)) { path_put_conditional(path, nd); return err; @@ -1504,7 +1523,7 @@ static int lookup_slow(struct nameidata *nd, struct path *path) return PTR_ERR(dentry); path->mnt = nd->path.mnt; path->dentry = dentry; - err = follow_managed(path, nd->flags); + err = follow_managed(path, nd); if (unlikely(err < 0)) { path_put_conditional(path, nd); return err; @@ -1620,7 +1639,7 @@ static inline int nested_symlink(struct path *path, struct nameidata *nd) { int res; - if (unlikely(current->link_count >= MAX_NESTED_LINKS)) { + if (unlikely(nd->link_count >= MAX_NESTED_LINKS)) { path_put_conditional(path, nd); path_put(&nd->path); return -ELOOP; @@ -1628,7 +1647,7 @@ static inline int nested_symlink(struct path *path, struct nameidata *nd) BUG_ON(nd->depth >= MAX_NESTED_LINKS); nd->depth++; - current->link_count++; + nd->link_count++; do { struct path link = *path; @@ -1641,7 +1660,7 @@ static inline int nested_symlink(struct path *path, struct nameidata *nd) put_link(nd, &link, cookie); } while (res > 0); - current->link_count--; + nd->link_count--; nd->depth--; return res; } @@ -1948,7 +1967,7 @@ static int path_init(int dfd, const struct filename *name, unsigned int flags, rcu_read_unlock(); return -ECHILD; done: - current->total_link_count = 0; + nd->total_link_count = 0; return link_path_walk(s, nd); } @@ -2027,7 +2046,10 @@ static int path_lookupat(int dfd, const struct filename *name, static int filename_lookup(int dfd, struct filename *name, unsigned int flags, struct nameidata *nd) { - int retval = path_lookupat(dfd, name, flags | LOOKUP_RCU, nd); + int retval; + struct nameidata *saved_nd = set_nameidata(nd); + + retval = path_lookupat(dfd, name, flags | LOOKUP_RCU, nd); if (unlikely(retval == -ECHILD)) retval = path_lookupat(dfd, name, flags, nd); if (unlikely(retval == -ESTALE)) @@ -2035,6 +2057,7 @@ static int filename_lookup(int dfd, struct filename *name, if (likely(!retval)) audit_inode(name, nd->path.dentry, flags & LOOKUP_PARENT); + set_nameidata(saved_nd); return retval; } @@ -2341,7 +2364,7 @@ static int path_mountpoint(int dfd, const struct filename *name, struct path *path, unsigned int flags) { - struct nameidata nd; + struct nameidata nd, *saved = set_nameidata(&nd); int err; err = path_init(dfd, name, flags, &nd); @@ -2364,6 +2387,7 @@ path_mountpoint(int dfd, const struct filename *name, struct path *path, } out: path_cleanup(&nd); + set_nameidata(saved); return err; } @@ -3026,7 +3050,7 @@ retry_lookup: if ((open_flag & (O_EXCL | O_CREAT)) == (O_EXCL | O_CREAT)) goto exit_dput; - error = follow_managed(path, nd->flags); + error = follow_managed(path, nd); if (error < 0) goto exit_dput; @@ -3215,12 +3239,14 @@ static struct file *path_openat(int dfd, struct filename *pathname, struct path path; int opened = 0; int error; + struct nameidata *saved_nd; file = get_empty_filp(); if (IS_ERR(file)) return file; file->f_flags = op->open_flag; + saved_nd = set_nameidata(nd); if (unlikely(file->f_flags & __O_TMPFILE)) { error = do_tmpfile(dfd, pathname, nd, flags, op, file, &opened); @@ -3267,6 +3293,7 @@ out: } file = ERR_PTR(error); } + set_nameidata(saved_nd); return file; } @@ -4427,18 +4454,20 @@ EXPORT_SYMBOL(readlink_copy); */ int generic_readlink(struct dentry *dentry, char __user *buffer, int buflen) { - struct nameidata nd; + struct nameidata nd, *saved = set_nameidata(&nd); void *cookie; int res; nd.depth = 0; cookie = dentry->d_inode->i_op->follow_link(dentry, &nd); if (IS_ERR(cookie)) - return PTR_ERR(cookie); - - res = readlink_copy(buffer, buflen, nd_get_link(&nd)); - if (dentry->d_inode->i_op->put_link) - dentry->d_inode->i_op->put_link(dentry, &nd, cookie); + res = PTR_ERR(cookie); + else { + res = readlink_copy(buffer, buflen, nd_get_link(&nd)); + if (dentry->d_inode->i_op->put_link) + dentry->d_inode->i_op->put_link(dentry, &nd, cookie); + } + set_nameidata(saved); return res; } EXPORT_SYMBOL(generic_readlink); diff --git a/include/linux/sched.h b/include/linux/sched.h index a419b65..4402c91 100644 --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -1447,7 +1447,7 @@ struct task_struct { it with task_lock()) - initialized normally by setup_new_exec */ /* file system info */ - int link_count, total_link_count; + struct nameidata *nameidata; #ifdef CONFIG_SYSVIPC /* ipc stuff */ struct sysv_sem sysvsem; -- 2.1.4