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 15/20] VFS/namei: enhance follow_link to support RCU-walk.
Date: Mon, 23 Mar 2015 13:37:40 +1100 [thread overview]
Message-ID: <20150323023740.8161.13594.stgit@notabene.brown> (raw)
In-Reply-To: <20150323023258.8161.32467.stgit@notabene.brown>
If LOOKUP_RCU is set, follow_link will not take/drop reference counts.
Replace cond_resched() with _cond_resched() as the latter
is a no-op if rcu_read_lock() is held while the former will
give a warning in that case.
After taking a copy of dentry->d_inode, check d_seq to ensure this
is still the symlink we were looking for.
Signed-off-by: NeilBrown <neilb@suse.de>
---
fs/namei.c | 27 +++++++++++++++++++--------
1 file changed, 19 insertions(+), 8 deletions(-)
diff --git a/fs/namei.c b/fs/namei.c
index 72f5a4f91855..40ff4cb04244 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -897,16 +897,21 @@ follow_link(struct path *link, struct nameidata *nd, void **p)
char *s;
nd->flags &= ~LOOKUP_LINK_RCU;
- if (nd->flags & LOOKUP_RCU)
+ if (nd->flags & LOOKUP_RCU) {
nd->flags |= LOOKUP_LINK_RCU;
- else if (link->mnt == nd->path.mnt)
+ if (__read_seqcount_retry(&dentry->d_seq, nd->seq)) {
+ error = -ECHILD;
+ goto out_put_nd_path;
+ }
+ } else if (link->mnt == nd->path.mnt)
mntget(link->mnt);
error = -ELOOP;
if (unlikely(nd->total_link_count >= 40))
goto out_put_nd_path;
- cond_resched();
+ /* If rcu_read_locked(), this will not resched, and will not warn */
+ _cond_resched();
nd->total_link_count++;
if (nd->flags & LOOKUP_RCU) {
@@ -938,11 +943,17 @@ follow_link(struct path *link, struct nameidata *nd, void **p)
return PTR_ERR(s);
}
if (*s == '/') {
- if (!nd->root.mnt)
- set_root(nd);
- path_put(&nd->path);
- nd->path = nd->root;
- path_get(&nd->root);
+ if (nd->flags & LOOKUP_RCU) {
+ if (!nd->root.mnt)
+ set_root_rcu(nd);
+ nd->path = nd->root;
+ } else {
+ if (!nd->root.mnt)
+ set_root(nd);
+ path_put(&nd->path);
+ nd->path = nd->root;
+ path_get(&nd->root);
+ }
nd->flags |= LOOKUP_JUMPED;
}
nd->inode = nd->path.dentry->d_inode;
next prev parent reply other threads:[~2015-03-23 2:39 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 ` [PATCH 12/20] VFS/namei: new flag to support RCU symlinks: LOOKUP_LINK_RCU NeilBrown
2015-03-23 2:37 ` NeilBrown [this message]
2015-03-25 23:23 ` [PATCH 00/20] Support follow_link in RCU-walk - V3 NeilBrown
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