[v3,109/110] namei: handle absolute symlinks without dropping out of RCU mode

Commit Message

Al Viro May 11, 2015, 6:08 p.m. UTC

From: Al Viro <[e-mail]>

Signed-off-by: Al Viro <[e-mail]>
---
 fs/namei.c | 30 +++++++++++++++++++-----------
 1 file changed, 19 insertions(+), 11 deletions(-)

Comments

Al Viro May 15, 2015, 5:11 a.m. UTC | #1

On Mon, May 11, 2015 at 07:08:09PM +0100, Al Viro wrote:
> @@ -499,7 +499,7 @@ struct nameidata {
>  	struct path	root;
>  	struct inode	*inode; /* path.dentry.d_inode */
>  	unsigned int	flags;
> -	unsigned	seq, m_seq;
> +	unsigned	seq, m_seq, root_seq;
>  	int		last_type;
>  	unsigned	depth;
>  	int		total_link_count;
> @@ -780,14 +780,14 @@ static __always_inline void set_root(struct nameidata *nd)
>  static __always_inline unsigned set_root_rcu(struct nameidata *nd)
>  {
>  	struct fs_struct *fs = current->fs;
> -	unsigned seq, res;
> +	unsigned seq;
>  
>  	do {
>  		seq = read_seqcount_begin(&fs->seq);
>  		nd->root = fs->root;
> -		res = __read_seqcount_begin(&nd->root.dentry->d_seq);
> +		nd->root_seq = __read_seqcount_begin(&nd->root.dentry->d_seq);

nd->root_seq is also needed in LOOKUP_ROOT | LOOKUP_RCU case.  Fixed and
folded.
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Patch

diff --git a/fs/namei.c b/fs/namei.c
index 1771143..fc8df8b 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -499,7 +499,7 @@  struct nameidata {
 	struct path	root;
 	struct inode	*inode; /* path.dentry.d_inode */
 	unsigned int	flags;
-	unsigned	seq, m_seq;
+	unsigned	seq, m_seq, root_seq;
 	int		last_type;
 	unsigned	depth;
 	int		total_link_count;
@@ -780,14 +780,14 @@  static __always_inline void set_root(struct nameidata *nd)
 static __always_inline unsigned set_root_rcu(struct nameidata *nd)
 {
 	struct fs_struct *fs = current->fs;
-	unsigned seq, res;
+	unsigned seq;
 
 	do {
 		seq = read_seqcount_begin(&fs->seq);
 		nd->root = fs->root;
-		res = __read_seqcount_begin(&nd->root.dentry->d_seq);
+		nd->root_seq = __read_seqcount_begin(&nd->root.dentry->d_seq);
 	} while (read_seqcount_retry(&fs->seq, seq));
-	return res;
+	return nd->root_seq;
 }
 
 static void path_put_conditional(struct path *path, struct nameidata *nd)
@@ -988,15 +988,23 @@  const char *get_link(struct nameidata *nd)
 	}
 	if (*res == '/') {
 		if (nd->flags & LOOKUP_RCU) {
-			if (unlikely(unlazy_walk(nd, NULL, 0)))
+			struct dentry *d;
+			if (!nd->root.mnt)
+				set_root_rcu(nd);
+			nd->path = nd->root;
+			d = nd->path.dentry;
+			nd->inode = d->d_inode;
+			nd->seq = nd->root_seq;
+			if (unlikely(read_seqcount_retry(&d->d_seq, nd->seq)))
 				return ERR_PTR(-ECHILD);
+		} else {
+			if (!nd->root.mnt)
+				set_root(nd);
+			path_put(&nd->path);
+			nd->path = nd->root;
+			path_get(&nd->root);
+			nd->inode = nd->path.dentry->d_inode;
 		}
-		if (!nd->root.mnt)
-			set_root(nd);
-		path_put(&nd->path);
-		nd->path = nd->root;
-		path_get(&nd->root);
-		nd->inode = nd->path.dentry->d_inode;
 		nd->flags |= LOOKUP_JUMPED;
 		while (unlikely(*++res == '/'))
 			;