From: NeilBrown <neilb@suse.de>
To: Al Viro <viro@ZenIV.linux.org.uk>
Cc: linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: [PATCH 12/20] VFS/namei: new flag to support RCU symlinks: LOOKUP_LINK_RCU.
Date: Mon, 23 Mar 2015 13:37:40 +1100 [thread overview]
Message-ID: <20150323023739.8161.59221.stgit@notabene.brown> (raw)
In-Reply-To: <20150323023258.8161.32467.stgit@notabene.brown>
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 <neilb@suse.de>
---
fs/namei.c | 18 +++++++++++++-----
include/linux/namei.h | 1 +
2 files changed, 14 insertions(+), 5 deletions(-)
diff --git a/fs/namei.c b/fs/namei.c
index 1a8cc0e47df6..3262c8c2e73d 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -552,6 +552,9 @@ 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()
@@ -765,7 +768,8 @@ 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_get_link(nd), cookie);
- path_put(link);
+ if (!(nd->flags & LOOKUP_LINK_RCU))
+ path_put(link);
}
int sysctl_protected_symlinks __read_mostly = 0;
@@ -892,9 +896,10 @@ 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;
@@ -946,7 +951,8 @@ 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;
}
@@ -1669,6 +1675,8 @@ static inline int nested_symlink(struct path *path, struct nameidata *nd)
nd->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 cc8b51a47160..633101964520 100644
--- a/include/linux/namei.h
+++ b/include/linux/namei.h
@@ -31,6 +31,7 @@ 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
next prev parent reply other threads:[~2015-03-23 2:37 UTC|newest]
Thread overview: 29+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-03-23 2:37 [PATCH 00/20] Support follow_link in RCU-walk - V3 NeilBrown
2015-03-23 2:37 ` [PATCH 02/20] STAGING/lustre: limit follow_link recursion using stack space NeilBrown
2015-04-18 3:01 ` Al Viro
2015-04-19 20:57 ` Andreas Dilger
2015-04-19 21:33 ` Al Viro
2015-04-20 2:29 ` Al Viro
2015-03-23 2:37 ` [PATCH 03/20] VFS: replace {, total_}link_count in task_struct with pointer to nameidata NeilBrown
2015-03-23 2:37 ` [PATCH 01/20] Documentation: remove outdated information from automount-support.txt NeilBrown
2015-03-23 2:37 ` [PATCH 10/20] security: make inode_follow_link RCU-walk aware NeilBrown
2015-03-23 2:37 ` [PATCH 04/20] ovl: rearrange ovl_follow_link to it doesn't need to call ->put_link NeilBrown
2015-03-23 2:37 ` [PATCH 07/20] VFS: remove nameidata args from ->follow_link NeilBrown
2015-03-23 2:37 ` [PATCH 06/20] SECURITY: remove nameidata arg from inode_follow_link NeilBrown
2015-03-23 2:37 ` [PATCH 05/20] VFS: replace nameidata arg to ->put_link with a char* NeilBrown
2015-03-23 2:37 ` [PATCH 09/20] security/selinux: pass 'flags' arg to avc_audit() and avc_has_perm_flags() NeilBrown
2015-03-23 2:37 ` [PATCH 11/20] VFS/namei: use terminate_walk when symlink lookup fails NeilBrown
2015-03-23 2:37 ` [PATCH 08/20] VFS: make all ->follow_link handlers aware for LOOKUP_RCU NeilBrown
2015-03-23 2:37 ` [PATCH 13/20] VFS/namei: abort RCU-walk on symlink if atime needs updating NeilBrown
2015-03-23 2:37 ` [PATCH 14/20] VFS/namei: add 'inode' arg to put_link() NeilBrown
2015-04-17 16:25 ` Al Viro
2015-04-17 19:09 ` Al Viro
2015-04-18 8:09 ` Al Viro
2015-03-23 2:37 ` [PATCH 16/20] VFS/namei: enable RCU-walk when following symlinks NeilBrown
2015-03-23 2:37 ` [PATCH 19/20] XFS: allow follow_link to often succeed in RCU-walk NeilBrown
2015-03-23 2:37 ` [PATCH 20/20] NFS: support LOOKUP_RCU in nfs_follow_link NeilBrown
2015-03-23 2:37 ` [PATCH 18/20] xfs: use RCU to free 'struct xfs_mount' NeilBrown
2015-03-23 2:37 ` [PATCH 17/20] VFS/namei: handle LOOKUP_RCU in page_follow_link_light NeilBrown
2015-03-23 2:37 ` NeilBrown [this message]
2015-03-23 2:37 ` [PATCH 15/20] VFS/namei: enhance follow_link to support RCU-walk NeilBrown
2015-03-25 23:23 ` [PATCH 00/20] Support follow_link in RCU-walk - V3 NeilBrown
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20150323023739.8161.59221.stgit@notabene.brown \
--to=neilb@suse.de \
--cc=linux-fsdevel@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=viro@ZenIV.linux.org.uk \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).