From mboxrd@z Thu Jan 1 00:00:00 1970 From: ebiederm@xmission.com (Eric W. Biederman) Subject: [PATCH review 6/6] vfs: Cache the results of path_connected Date: Mon, 03 Aug 2015 16:30:54 -0500 Message-ID: <8738009i0h.fsf_-_@x220.int.ebiederm.org> References: <871tncuaf6.fsf@x220.int.ebiederm.org> <87mw5xq7lt.fsf@x220.int.ebiederm.org> <87a8yqou41.fsf_-_@x220.int.ebiederm.org> <874moq9oyb.fsf_-_@x220.int.ebiederm.org> <871tfkawu9.fsf_-_@x220.int.ebiederm.org> Mime-Version: 1.0 Content-Type: text/plain Cc: , Al Viro , Andy Lutomirski , "Serge E. Hallyn" , Richard Weinberger , Andrey Vagin , Jann Horn , Willy Tarreau , Omar Sandoval , Miklos Szeredi , Linus Torvalds , "J. Bruce Fields" To: Linux Containers Return-path: Received: from out03.mta.xmission.com ([166.70.13.233]:56091 "EHLO out03.mta.xmission.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755177AbbHCVhs (ORCPT ); Mon, 3 Aug 2015 17:37:48 -0400 In-Reply-To: <871tfkawu9.fsf_-_@x220.int.ebiederm.org> (Eric W. Biederman's message of "Mon, 03 Aug 2015 16:25:18 -0500") Sender: linux-fsdevel-owner@vger.kernel.org List-ID: Add a new field mnt_escape_count in nameidata, initialize it to 0 and cache the value of read_mnt_escape_count in nd->mnt_escape_count. This allows a single check in path_connected in the common case where either the mount has had no escapes (mnt_escape_count == 0) or there has been an escape and it has been validated that the current path does not escape. To keep the cache valid nd->mnt_escape_count must be set to 0 whenever the nd->path.mnt changes or when nd->path.dentry changes such that the connectedness of the previous value of nd->path.dentry does not imply the connected of the new value of nd->path.dentry. Various locations in fs/namei.c are updated to set nd->mnt_escape_count to 0 as necessary. Signed-off-by: "Eric W. Biederman" --- fs/namei.c | 26 +++++++++++++++++++++++--- 1 file changed, 23 insertions(+), 3 deletions(-) diff --git a/fs/namei.c b/fs/namei.c index bccd3810ff60..79a5dca073f5 100644 --- a/fs/namei.c +++ b/fs/namei.c @@ -514,6 +514,7 @@ struct nameidata { struct nameidata *saved; unsigned root_seq; int dfd; + unsigned mnt_escape_count; }; static void set_nameidata(struct nameidata *p, int dfd, struct filename *name) @@ -572,12 +573,13 @@ static bool path_connected(struct nameidata *nd) struct vfsmount *mnt = nd->path.mnt; unsigned escape_count = read_mnt_escape_count(mnt); - if (likely(escape_count == 0)) + if (likely(escape_count == nd->mnt_escape_count)) return true; if (!is_subdir(nd->path.dentry, mnt->mnt_root)) return false; + cache_mnt_escape_count(&nd->mnt_escape_count, escape_count); return true; } @@ -840,6 +842,9 @@ static inline void path_to_nameidata(const struct path *path, if (nd->path.mnt != path->mnt) mntput(nd->path.mnt); } + if (unlikely((nd->path.mnt != path->mnt) || + (nd->path.dentry != path->dentry->d_parent))) + nd->mnt_escape_count = 0; nd->path.mnt = path->mnt; nd->path.dentry = path->dentry; } @@ -856,6 +861,7 @@ void nd_jump_link(struct path *path) nd->path = *path; nd->inode = nd->path.dentry->d_inode; nd->flags |= LOOKUP_JUMPED; + nd->mnt_escape_count = 0; } static inline void put_link(struct nameidata *nd) @@ -1040,6 +1046,7 @@ const char *get_link(struct nameidata *nd) nd->inode = nd->path.dentry->d_inode; } nd->flags |= LOOKUP_JUMPED; + nd->mnt_escape_count = 0; while (unlikely(*++res == '/')) ; } @@ -1335,6 +1342,7 @@ static int follow_dotdot_rcu(struct nameidata *nd) nd->path.mnt = &mparent->mnt; inode = inode2; nd->seq = seq; + nd->mnt_escape_count = 0; } } while (unlikely(d_mountpoint(nd->path.dentry))) { @@ -1348,6 +1356,7 @@ static int follow_dotdot_rcu(struct nameidata *nd) nd->path.dentry = mounted->mnt.mnt_root; inode = nd->path.dentry->d_inode; nd->seq = read_seqcount_begin(&nd->path.dentry->d_seq); + nd->mnt_escape_count = 0; } nd->inode = inode; return 0; @@ -1406,8 +1415,9 @@ EXPORT_SYMBOL(follow_down); /* * Skip to top of mountpoint pile in refwalk mode for follow_dotdot() */ -static void follow_mount(struct path *path) +static bool follow_mount(struct path *path) { + bool followed = false; while (d_mountpoint(path->dentry)) { struct vfsmount *mounted = lookup_mnt(path); if (!mounted) @@ -1416,7 +1426,9 @@ static void follow_mount(struct path *path) mntput(path->mnt); path->mnt = mounted; path->dentry = dget(mounted->mnt_root); + followed = true; } + return followed; } static int follow_dotdot(struct nameidata *nd) @@ -1444,8 +1456,10 @@ static int follow_dotdot(struct nameidata *nd) } if (!follow_up(&nd->path)) break; + nd->mnt_escape_count = 0; } - follow_mount(&nd->path); + if (follow_mount(&nd->path)) + nd->mnt_escape_count = 0; nd->inode = nd->path.dentry->d_inode; return 0; } @@ -1997,6 +2011,7 @@ static const char *path_init(struct nameidata *nd, unsigned flags) nd->flags = flags | LOOKUP_JUMPED | LOOKUP_PARENT; nd->depth = 0; nd->total_link_count = 0; + nd->mnt_escape_count = 0; if (flags & LOOKUP_ROOT) { struct dentry *root = nd->root.dentry; struct inode *inode = root->d_inode; @@ -3026,6 +3041,7 @@ static int do_last(struct nameidata *nd, unsigned seq; struct inode *inode; struct path save_parent = { .dentry = NULL, .mnt = NULL }; + unsigned save_parent_escape_count = 0; struct path path; bool retried = false; int error; @@ -3155,6 +3171,9 @@ finish_lookup: } else { save_parent.dentry = nd->path.dentry; save_parent.mnt = mntget(path.mnt); + save_parent_escape_count = nd->mnt_escape_count; + if (nd->path.dentry != path.dentry->d_parent) + nd->mnt_escape_count = 0; nd->path.dentry = path.dentry; } @@ -3227,6 +3246,7 @@ stale_open: BUG_ON(save_parent.dentry != dir); path_put(&nd->path); + nd->mnt_escape_count = save_parent_escape_count; nd->path = save_parent; nd->inode = dir->d_inode; save_parent.mnt = NULL; -- 2.2.1