namei: handle absolute symlinks without dropping out of RCU mode

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

1 files changed, 20 insertions, 11 deletions

diff --git a/fs/namei.c b/fs/namei.c
index bf46e1010a74..a5ed0d070a20 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;
@@ -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);