namei: handle absolute symlinks without dropping out of RCU mode

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

diff --git a/fs/namei.c b/fs/namei.c
index bf46e1010a744aaa50e686f46a3c913246de1b31..a5ed0d070a2057741cd579482039b3f9538dd2a2 100644 (file)
--- 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;
@@ -788,14 +788,14 @@ 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)
@@ -995,15 +995,23 @@ 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 == '/'))
                        ;
@@ -1979,6 +1987,7 @@ static const char *path_init(int dfd, const struct filename *name,
                if (flags & LOOKUP_RCU) {
                        rcu_read_lock();
                        nd->seq = __read_seqcount_begin(&nd->path.dentry->d_seq);
+                       nd->root_seq = nd->seq;
                        nd->m_seq = read_seqbegin(&mount_lock);
                } else {
                        path_get(&nd->path);