namei.c: split unlazy_walk()

In all but one case, the last two arguments are NULL and 0 resp.;
almost everyone just wants to switch nameidata to non-RCU mode.
The only exception is lookup_fast(), where we have a child dentry
we want to legitimize as well.  Split these two cases.

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

diff --git a/fs/namei.c b/fs/namei.c
index 2ed2701..76cfeb6 100644 (file)
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -672,17 +672,15 @@ static bool legitimize_links(struct nameidata *nd)
 /**
  * unlazy_walk - try to switch to ref-walk mode.
  * @nd: nameidata pathwalk data
- * @dentry: child of nd->path.dentry or NULL
- * @seq: seq number to check dentry against
  * Returns: 0 on success, -ECHILD on failure
  *
- * unlazy_walk attempts to legitimize the current nd->path, nd->root and dentry
- * for ref-walk mode.  @dentry must be a path found by a do_lookup call on
- * @nd or NULL.  Must be called from rcu-walk context.
+ * unlazy_walk attempts to legitimize the current nd->path and nd->root
+ * for ref-walk mode.
+ * Must be called from rcu-walk context.
  * Nothing should touch nameidata between unlazy_walk() failure and
  * terminate_walk().
  */
-static int unlazy_walk(struct nameidata *nd, struct dentry *dentry, unsigned seq)
+static int unlazy_walk(struct nameidata *nd)
 {
        struct dentry *parent = nd->path.dentry;
 
@@ -691,33 +689,66 @@ static int unlazy_walk(struct nameidata *nd, struct dentry *dentry, unsigned seq
        nd->flags &= ~LOOKUP_RCU;
        if (unlikely(!legitimize_links(nd)))
                goto out2;
+       if (unlikely(!legitimize_path(nd, &nd->path, nd->seq)))
+               goto out1;
+       if (nd->root.mnt && !(nd->flags & LOOKUP_ROOT)) {
+               if (unlikely(!legitimize_path(nd, &nd->root, nd->root_seq)))
+                       goto out;
+       }
+       rcu_read_unlock();
+       BUG_ON(nd->inode != parent->d_inode);
+       return 0;
+
+out2:
+       nd->path.mnt = NULL;
+       nd->path.dentry = NULL;
+out1:
+       if (!(nd->flags & LOOKUP_ROOT))
+               nd->root.mnt = NULL;
+out:
+       rcu_read_unlock();
+       return -ECHILD;
+}
+
+/**
+ * unlazy_child - try to switch to ref-walk mode.
+ * @nd: nameidata pathwalk data
+ * @dentry: child of nd->path.dentry
+ * @seq: seq number to check dentry against
+ * Returns: 0 on success, -ECHILD on failure
+ *
+ * unlazy_child attempts to legitimize the current nd->path, nd->root and dentry
+ * for ref-walk mode.  @dentry must be a path found by a do_lookup call on
+ * @nd.  Must be called from rcu-walk context.
+ * Nothing should touch nameidata between unlazy_child() failure and
+ * terminate_walk().
+ */
+static int unlazy_child(struct nameidata *nd, struct dentry *dentry, unsigned seq)
+{
+       BUG_ON(!(nd->flags & LOOKUP_RCU));
+
+       nd->flags &= ~LOOKUP_RCU;
+       if (unlikely(!legitimize_links(nd)))
+               goto out2;
        if (unlikely(!legitimize_mnt(nd->path.mnt, nd->m_seq)))
                goto out2;
-       if (unlikely(!lockref_get_not_dead(&parent->d_lockref)))
+       if (unlikely(!lockref_get_not_dead(&nd->path.dentry->d_lockref)))
                goto out1;
 
        /*
-        * For a negative lookup, the lookup sequence point is the parents
-        * sequence point, and it only needs to revalidate the parent dentry.
-        *
-        * For a positive lookup, we need to move both the parent and the
-        * dentry from the RCU domain to be properly refcounted. And the
-        * sequence number in the dentry validates *both* dentry counters,
-        * since we checked the sequence number of the parent after we got
-        * the child sequence number. So we know the parent must still
-        * be valid if the child sequence number is still valid.
+        * We need to move both the parent and the dentry from the RCU domain
+        * to be properly refcounted. And the sequence number in the dentry
+        * validates *both* dentry counters, since we checked the sequence
+        * number of the parent after we got the child sequence number. So we
+        * know the parent must still be valid if the child sequence number is
         */
-       if (!dentry) {
-               if (read_seqcount_retry(&parent->d_seq, nd->seq))
-                       goto out;
-               BUG_ON(nd->inode != parent->d_inode);
-       } else {
-               if (!lockref_get_not_dead(&dentry->d_lockref))
-                       goto out;
-               if (read_seqcount_retry(&dentry->d_seq, seq))
-                       goto drop_dentry;
+       if (unlikely(!lockref_get_not_dead(&dentry->d_lockref)))
+               goto out;
+       if (unlikely(read_seqcount_retry(&dentry->d_seq, seq))) {
+               rcu_read_unlock();
+               dput(dentry);
+               goto drop_root_mnt;
        }
-
        /*
         * Sequence counts matched. Now make sure that the root is
         * still valid and get it if required.
@@ -733,10 +764,6 @@ static int unlazy_walk(struct nameidata *nd, struct dentry *dentry, unsigned seq
        rcu_read_unlock();
        return 0;
 
-drop_dentry:
-       rcu_read_unlock();
-       dput(dentry);
-       goto drop_root_mnt;
 out2:
        nd->path.mnt = NULL;
 out1:
@@ -775,7 +802,7 @@ static int complete_walk(struct nameidata *nd)
        if (nd->flags & LOOKUP_RCU) {
                if (!(nd->flags & LOOKUP_ROOT))
                        nd->root.mnt = NULL;
-               if (unlikely(unlazy_walk(nd, NULL, 0)))
+               if (unlikely(unlazy_walk(nd)))
                        return -ECHILD;
        }
 
@@ -1001,7 +1028,7 @@ const char *get_link(struct nameidata *nd)
                touch_atime(&last->link);
                cond_resched();
        } else if (atime_needs_update_rcu(&last->link, inode)) {
-               if (unlikely(unlazy_walk(nd, NULL, 0)))
+               if (unlikely(unlazy_walk(nd)))
                        return ERR_PTR(-ECHILD);
                touch_atime(&last->link);
        }
@@ -1020,7 +1047,7 @@ const char *get_link(struct nameidata *nd)
                if (nd->flags & LOOKUP_RCU) {
                        res = get(NULL, inode, &last->done);
                        if (res == ERR_PTR(-ECHILD)) {
-                               if (unlikely(unlazy_walk(nd, NULL, 0)))
+                               if (unlikely(unlazy_walk(nd)))
                                        return ERR_PTR(-ECHILD);
                                res = get(dentry, inode, &last->done);
                        }
@@ -1529,7 +1556,7 @@ static int lookup_fast(struct nameidata *nd,
                bool negative;
                dentry = __d_lookup_rcu(parent, &nd->last, &seq);
                if (unlikely(!dentry)) {
-                       if (unlazy_walk(nd, NULL, 0))
+                       if (unlazy_walk(nd))
                                return -ECHILD;
                        return 0;
                }
@@ -1567,7 +1594,7 @@ static int lookup_fast(struct nameidata *nd,
                        if (likely(__follow_mount_rcu(nd, path, inode, seqp)))
                                return 1;
                }
-               if (unlazy_walk(nd, dentry, seq))
+               if (unlazy_child(nd, dentry, seq))
                        return -ECHILD;
                if (unlikely(status == -ECHILD))
                        /* we'd been told to redo it in non-rcu mode */
@@ -1646,7 +1673,7 @@ static inline int may_lookup(struct nameidata *nd)
                int err = inode_permission(nd->inode, MAY_EXEC|MAY_NOT_BLOCK);
                if (err != -ECHILD)
                        return err;
-               if (unlazy_walk(nd, NULL, 0))
+               if (unlazy_walk(nd))
                        return -ECHILD;
        }
        return inode_permission(nd->inode, MAY_EXEC);
@@ -1690,7 +1717,7 @@ static int pick_link(struct nameidata *nd, struct path *link,
                                if (!(nd->flags & LOOKUP_ROOT))
                                        nd->root.mnt = NULL;
                                rcu_read_unlock();
-                       } else if (likely(unlazy_walk(nd, NULL, 0)) == 0)
+                       } else if (likely(unlazy_walk(nd)) == 0)
                                error = nd_alloc_stack(nd);
                }
                if (error) {
@@ -2108,7 +2135,7 @@ OK:
                }
                if (unlikely(!d_can_lookup(nd->path.dentry))) {
                        if (nd->flags & LOOKUP_RCU) {
-                               if (unlazy_walk(nd, NULL, 0))
+                               if (unlazy_walk(nd))
                                        return -ECHILD;
                        }
                        return -ENOTDIR;
@@ -2565,7 +2592,7 @@ mountpoint_last(struct nameidata *nd)
 
        /* If we're in rcuwalk, drop out of it to handle last component */
        if (nd->flags & LOOKUP_RCU) {
-               if (unlazy_walk(nd, NULL, 0))
+               if (unlazy_walk(nd))
                        return -ECHILD;
        }